Calculated Industries 8703 Hot Rod Calc User guide

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Designing and building the Hot Rod Calc™ could not have been done without the support and input from individuals knowledgeable in all aspects of motorsports racing, especially those with deep understanding of the relationship between weather conditions and engine performance.

Calculated Industries gratefully acknowledges

Patrick Hale (Drag Racing Pro) and Marko

Glush (independent engine builder and bracket racer) for their generous time and expertise during the development of this calculator.

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The

Hot Rod Calc™ Road and Strip Performance Calculator is specifically designed for today’s hot rod owner/builders, drag and bracket racers, engine builders, and car and truck enthusiasts.

Whether you’re into hot rods, street performance, off-road, or drag racing, the Hot Rod Calc can help with its built-in solutions for carburetor size, volumetric efficiency, tire ratios, gear ratios, engine displacement, compression ratio, HP, torque, and RPM. In addition to solutions for performance modifications, the Hot Rod Calc also includes features for predicting elapsed time and trap speed at

1/8 and 1/4 mile intervals. The Hot Rod Calc is a powerful, costeffective tool for every performance car and truck owner’s toolbox.

Helps you at the track:

• Air Density Solutions

• Density Altitude Solutions

• Adjust your ET prediction with Horsepower and Motorsport

Standard Atmosphere Corrections

• Adjust your ET prediction with Wind Speed and Direction

Corrections

Helps you improve engine performance

• Calculate Carburetor Size, Engine Displacement, Bore and

Stroke

• Estimate Rear Wheel Horsepower, Flywheel Horsepower and

Torque

Answer hundreds of car and truck What If I... questions

• Calculate Effects of Changing Tire Sizes

• Speed, RPM, Gear Ratios, and Tire Relationships

• US/Metric Math Conversions and Solutions

• And more!

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TABLE OF CONTENTS

GETTING STARTED ......................................................................4

KEY DEFINITIONS .........................................................................4

Basic Function Keys .....................................................................4

Dimensional Function Keys ..........................................................5

Miscellaneous Function Keys .......................................................6

ET Prediction Keys .......................................................................6

PREFERENCE SETTINGS ........................................................... 11

ENTERING DIMENSIONS ............................................................12

Square and Cubic Dimensions ...................................................12

ENTERING CONVERSIONS ........................................................13

Distance/Length Conversions.....................................................13

Engine Displacement Conversions .............................................14

USING THE HOT ROD CALC .....................................................16

Important Terms and Definitions.................................................16

Motorsports Standard Atmosphere .........................................16

Horsepower Correction Factor ................................................ 17

Air Density Index ..................................................................... 17

Calculating ADI and Density Altitude Using

Calculating ADI and Density Altitude Using Elevation ................21

Calculating and Using a Fuel Correction Index .............................22

Calculating Water Vapor Content ...............................................25

Basic ET Prediction ....................................................................26

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ET Prediction and HPc ...............................................................27

ET Prediction and Wind Conditions ............................................30

Estimating Vehicle Weight ..........................................................32

Estimating Rear Wheel Horsepower .........................................33

Calculating Effects of Changing Tire Sizes ................................35

Speed, RPM, Gear Ratios, and Tire Relationships ....................37

Calculating Carburetor Size ........................................................40

Calculating Carburetor Size with a Known

Calculating Volumetric Efficiency ...............................................42

Estimating Flywheel Horsepower at a Known RPM ...................43

Estimating Flywheel Torque at a Known RPM ...........................44

Calculating Compression Ratio ..................................................44

Calculating Mill Amount ..............................................................48

Calculating Piston Speed............................................................49

Calculating Engine Displacement ............................................... 51

Calculating Bore and Stroke .......................................................53

APPENDIX A

Body Style and Drag Coefficients...............................................55

APPENDIX B

Holley Jet Chart and Jet Orifice Area Conversion Chart ............56

APPENDIX C

Default Settings .........................................................................60

APPENDIX D

Care Instructions .......................................................................61

APPENDIX E

Accuracy/Errors, Auto Shut-off, Batteries, Reset .......................62

WARRANTY, REPAIR AND RETURN INFORMATION ..............64

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GETTING STARTED

You may want to practice getting a feel for your calculator keys by reading through the key definitions and learning how to enter data, how to store values, etc., before proceeding to the examples.

KEY DEFINITIONS

Basic Function Keys

 

On/Clear Key – Turns on power. Pressing once clears the last entry and the display. Pressing twice clears all non-permanent values.

  Off – Turns all power off. Clears all non-permanent values.

  

  Arithmetic operation keys.



–

 and



Keys used for entering numbers.

 Convert – Used with the dimensional keys to convert between units or with other keys to access special functions.

  Recall – Used with other keys to recall stored values and settings.

 Memory Clear (M - R/C) – Clears Memory without changing current display.



Accumulative Memory – Adds value to Accumulative

Memory.

 (M-) – Subtracts value from Accumulative Memory.



Percentage – Used to find a given percent of a number.

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Dimensional Function Keys

 Millimeters – Identifies entry as millimeters, with repeated presses toggling between linear, area and volume units. Converts dimensional value to units of millimeters, with repeated presses toggling between millimeters and meters.

 Meters – Identifies entry as meters, with repeated presses toggling between linear, area and volume units.

Converts dimensional value to units of millimeters, with repeated presses toggling between millimeters and meters.

 Inch – Identifies entry as inches, with repeated presses toggling between linear, area and volume units. Converts dimensional value to units of inches, with repeated presses toggling between inches and feet.

 Feet – Identifies entry as feet, with repeated presses toggling between linear, area and volume units. Converts dimensional value to units of inches, with repeated presses toggling between inches and feet.

 Miles per Hour – Enters or converts to miles per hour

(MPH). Entry can be whole or decimal numbers.

 Kilometers per Hour – Enters or converts to kilometers per hour (km/h). Entry can be whole or decimal numbers.

 Identifies/Converts to pounds (lbs).

 Identifies/Converts to fluid ounces (fl oz).

 Identifies/Converts to degrees Celsius (° C).

 Identifies/Converts to degrees Fahrenheit (° F).

 Identifies/Converts to gallons (gal).

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 Identifies/Converts to liters (liters).

 Identifies/Converts to milliliters (mL).

 Identifies/Converts to pound-force foot (lb-ft).

 Identifies/Converts to cubic centimeters (cc).

 Identifies/Converts to Newton-meters (N-m).

 Identifies/Converts to kilograms (kg).

Miscellaneous Function Keys

 Calculates the square root of the number in the display.

 (1/x) Reciprocal – Finds the reciprocal of a number

(e.g., 8   0.125).

 Clear All – Returns all stored values to the default settings. (Does not affect Preference settings).

 Displays value of

π

(3.1415927).

 (+/ –) – Toggle displayed value between minus and plus value.

 Preference settings.

ET Prediction Keys

 Air Temperature – Enters the current local air temperature. Default value is 60 ° F.

 Enters the current local absolute pressure as reported by a weather meter such as an aircraft altimeter or absolute barometer (not corrected by Internet, local radio or TV news sources). Default value is 29.92 in Hg.

 Moisture – Enters the current local relative humidity;

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calculates current local water vapor pressure, saturation water vapor pressure, and dew point temperature.

Default value is 0% RH.

 Wind Speed – Enters current local wind speed; calculates corrected ET and speed.

  Elevation / Air Density Index – Enters current local elevation; calculates air density index and density altitude. Default elevation is 0 feet. Default air density index is 100%. Default density altitude is -0.001 feet

(effectively 0 feet).

 Wind Direction – Enters the current local wind direction.

A direct headwind is entered as 0°, a direct crosswind is entered as 90°, and a direct tailwind is entered as 180°.

You can enter a value from 0° to 360°.

 Vehicle Weight – Enters or calculates the vehicle’s weight. Vehicle weight typically includes the driver’s weight. Calculates vehicle weight given ET and HP or

MPH and HP.

 Frontal Area – Enters the vehicle’s frontal area when correcting for wind conditions. This is the view of the vehicle from “head-on”, measuring from bottom of front bumper to the top of the roof and the widest point to point of the race car (e.g. door handle to door handle).

 Elapsed Time – Enters or calculates the vehicle’s quarter-mile drag strip elapsed time in seconds; calculates the vehicles eighth-mile drag strip elapsed time in seconds; calculates the vehicle’s horsepower correction factor (HPc) and Motorsport Standard

Atmosphere (MSA) adjusted elapsed time and speed when the appropriate weather conditions are entered.

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 Drag Coefficient – Enters the vehicle’s drag coefficient when correcting for wind. See Appendix A for typical body styles and associated drag coefficient values.

Default value is 35%.

Performance Keys

 Tire Ratio – Calculates tire ratio, effective drive ratio, equivalent drive ratio, drive ratio, actual speed, and indicated (gauge) speed.

 Old Tire Diameter – Enters the current tire size for solving tire and gear ratio problems.

 Gear Ratio – Enters or calculates overall gear ratio, as well as gear ratios adjusted for manual and automatic transmissions.

 New Tire Diameter – Enters the new tire size for solving tire and gear ratio problems.

 Engine Displacement – Enter or calculate Engine

Displacement. Calculate given values for Bore, Stroke and number of Cylinders.

 # of Cylinders – Enter and store number of cylinders in an engine. Default is 8 cylinders.

 Compression Ratio – Calculate Compression Ratio given Bore diameter, Stroke length, Chamber Volume,

Gasket Bore Diameter, Gasket Thickness, Deck Height, and Dome Volume.

 Mill Amount – Calculates the amount to cut out of the cylinder’s head in order to increase compression ratio given values for Stroke, old Compression Ratio and new

Compression Ratio.

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 Piston Speed – Enter or calculate an engine’s Piston

Speed. Calculate Piston Speed given values for RPM and Stroke length.

 Mechanical Efficiency – Enters the engine’s mechanical efficiency, a numeric value representing a percentage of the power available inside the engine’s cylinders that makes its way to the flywheel (e.g. less friction losses from rings, pistons, bearing friction, oil pumps, etc.). Default value is 85%.

 Enter or calculate a Carburetor size as a flow rate.

Calculate Carburetor size given values for Engine

Displacement, RPM and Volumetric Efficiency.

 Volumetric Efficiency – Enter or calculate the volumetric efficiency of an engine. Calculate given values for Engine

Displacement, RPM and Carburetor Size.

 Bore – Enter or calculate Bore diameter. Use to calculate engine displacement, stroke or compression ratio. Calculate Bore given values for engine displacement and Stroke length.

 Gasket Bore – Enter and store Gasket Bore size. Used in calculating Compression Ratio.

 Stroke – Enter or calculate Stroke length. Use to calculate engine displacement, bore or compression ratio and piston speed. Calculate Stroke length given values for engine displacement and Bore diameter.

 Gasket Thickness – Enter and store Gasket Thickness.

Used in calculating Compression Ratio.

 RPM – Enter or calculate RPM. Calculate given values for Stroke and Piston Speed.

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 Deck Height – Enter and store cylinder Deck Height.


  Torque – Enter or calculate flywheel engine torque in lb-ft. Calculates Torque given RPM and Horsepower.

 Dome Volume – Enter and store Piston Dome Volume.


 Horsepower – Enter or calculate the engine horsepower; calculates Horsepower Correction Factor

(HPc) and Motorsport Standard Atmosphere (MSA) - adjusted horsepower when the appropriate weather conditions are entered; calculates flywheel horsepower given RPM and torque; calculates rear wheel horsepower given ET and Vehicle Weight.

 Chamber Volume – Enter and store cylinder Chamber

Volume. Used in calculating Compression Ratio.

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PREFERENCE SETTINGS

Press  , then  to access the Preferences menu. Continue pressing  to toggle through different Preferences. Press  or  keys to toggle between options of the different Preferences.

Press  to exit Preferences. Your calculator will keep

Preference settings until a Full Reset alters your settings to the default values.

KEYSTROKES DISPLAY







(Functional Rounding)

 (repeats options)

Second press of  : (Default Unit Format)




Third press of  : (Meter Rounding)

 


F-RND 0.000

F-RND 0.00

F-RND FLOAt

F-RND 0.000

US UNItS

METRC UNItS

US UNItS

METER 0.000 M

METER FLOAt M

METER 0.000 M

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ENTERING DIMENSIONS

Distance/Length Dimensions

Examples of how linear dimensions are entered

(press  after each entry):

DIMENSIONS KEYSTROKE

4.5 inches

95 millimeters

1320 feet

201 meters

   

  

    

   

Square and Cubic Dimensions

Examples of how square and cubic dimensions are entered

(press  after each entry):

DIMENSIONS KEYSTROKE

14 square inches

11 square millimeters

450 cubic inches

3 cubic feet

   

   

     

   

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ENTERING CONVERSIONS

Distance/Length Conversions

Enter and convert 1,320 feet to meters.




    

  *

0.

1320 F

402.336 M

* Repeated presses of  will toggle between meters and millimeters.

Enter and convert 4.5 inches to millimeters.




   

 

0.

4.5 IN

114.3 MM

* Repeated presses of  will toggle between meters and millimeters.

Speed Conversions

Enter and convert 65 miles per hour to kilometers per hour.




  



0.

SPEED S 65 MPH

SPEED S 104.60736 KM/H

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Engine Displacement Conversions

Enter and convert 450 cubic inches (CID) to liters.




     

 

Enter and convert 5.0 liters to CID.

0.

450 CU IN

LITER 7.3741788




 

 

0.

LITER 5

305.11872 CU IN

Torque Conversions

Enter and convert 42 lb-ft to Newton-meters.




  

 

0.

LB-FT 42

N-M 56.944354

Enter and convert 25 N-m to lb-ft




  

 

0.

N-M 25

LB-FT 18.439054

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Weight Conversions

Enter and convert 2700 pounds to kilograms.






    

0.

LBS 2700

KG 1224.6994

Volume Conversions

Enter and convert 5.5 gallons to liters.




   



0.

GAL 5.5

LITER 20.819765

Enter and convert 15.25 liters to gallons.




     



0.

LITER 15.25

GAL 4.0286238

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USING THE HOT ROD CALC

Note: The Hot Rod Calc’s built-in horsepower correction calculations are based on formulas designed for naturally aspirated gasoline burning engines.

The Hot Rod Calc helps you get the most out of your bracket racing efforts by assisting you at the dragstrip in two very critical ways:

• Calculates the air density index, based on your current local measured weather inputs, to assist you with changing your carburetor jet settings.

• Calculates a horsepower correction factor, based on your current local measured weather and/or track elevation inputs, to assist you with predicting changes in your engine’s performance enabling better ET and MPH predictions.

To further understand the Hot Rod Calc’s outputs and how to use the calculator, please get familiar with the following technical and weather related terms used throughout this section of the user’s guide.

Important Terms and Definitions

MSA*

Motorsports Standard Atmosphere, MSA, is a term defined by Drag Racing Pro’s Patrick Hale, and is a methodology implemented in this calculator. Simply stated, it is a standard, reference set of ambient weather conditions. Engine and race car performance can be corrected back to MSA in order to understand the affects of weather changes.

As a rule, if the local weather changes, so does your vehicle’s performance. Some basic guidelines to know are that the higher the absolute pressure, the faster your vehicle will go, but the higher the temperature, the

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slower it will go. More specifically, engine performance is impacted by the ambient air’s density.

MSA includes three parameters: absolute pressure (29.92 in Hg), temperature (60° F), and relative humidity (0% RH, or “dry air”).

HPc*

The Horsepower Correction Factor is calculated and implemented within HP, ET, and MPH estimations on the

Hot Rod Calc. The current local weather conditions and/or elevation entered into the calculator are used to calculate

HPc.

As a guideline, the closer the HPc is to 1.0, the faster the vehicle will run (more horsepower is produced).

Conversely, the higher the HPc, the slower it will run (less horsepower is produced).

* Patrick Hale, “Motorsports Standard Atmosphere and Weather

Correction Methods”, Arizona: DRPro, 2008.

Density Altitude

Density Altitude is an MSA elevation that has the same air density as the current, local measured weather conditions.

Meaning, your physical elevation might be 4,000 feet above sea level, but the current air conditions are like a

“theoretical” perfect day at 5,000 feet. Density Altitude is simply a corrected elevation, and is calculated using the current, local measured weather conditions entered into the calculator.

Air Density Index

Air Density Index, ADI, is a ratio (expressed as a percentage) of the current air’s density to that of MSA.

The ADI at MSA is 100%. ADI is calculated using the

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current, local measured weather conditions entered into the calculator. Once you have established an air/fuel ratio for the current track and weather conditions, calculate and record the current ADI.

As a rule, ADI will be less than 100% for elevations above sea level as well as for temperatures above 60° F.

Conversely, ADI will be more than 100% for temperatures below 60° F.

As a guideline, ADI can be used to tune your engine’s air/fuel requirements when conditions change from your baseline conditions. For each percentage point the current

ADI is above your recorded baseline ADI, your engine will require that much more fuel. Conversely, for each percentage point the current ADI is below your recorded baseline ADI, your engine will require that much less fuel to maintain the same level of performance.

Be careful! It’s safer to be 3% rich than to be 1% lean.

ADI can tell you a lot about what you need to know for carburetor jetting changes, however, you must understand all the relationships before making a change. Surging or hesitating will indicate that your vehicle is likely running too lean an air/fuel ratio. If you’re seeing black smoke out the exhaust, it is likely you are running too rich an air/ fuel ratio. Combine your experience with theory, always refer to your carburetor manufacturer’s jetting size and change instructions, and make air/fuel changes in small, incremental steps.

Lastly, data is knowledge, and knowledge is power!

Always record your air/fuel and jet number settings along with the Hot Rod Calc’s calculated ADI and density altitude for those last minute adjustments as weather conditions change throughout the day or for dialing in at different track locations.

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Pressure

There are two types of commonly referenced pressure,

Absolute Pressure and Corrected Pressure.

Absolute Pressure is the actual, ambient local pressure.

There are several tools available to help you measure

Absolute Pressure, such as altimeters, absolute barometers, and motorsports weather stations. You do not need to know your track’s elevation when utilizing

Absolute Pressure on your calculator.

Corrected Pressure is a measurement you might get from the local radio station, TV station, from the Internet, or from a “corrected” barometer. It is corrected for sealevel and is not suitable for motorsports. Do not use

Corrected Pressure on the Hot Rod Calc.

Elapsed Time

Elapsed Time, or ET, is the amount of time in seconds it takes a vehicle to travel from start to finish over a measured distance, typically one quarter of a mile.

Your calculator’s ET predictions may vary from other

ET prediction sources primarily due to traction. The Hot

Rod Calc assumes ideal conditions with no tire slippage and 100% converter lockup, and the predictions are for estimation purposes only.

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Calculating ADI and Density Altitude

Using Absolute Pressure

For this example, you are at the Los Angeles County Fairplex

Auto Club Raceway in Pomona, Calif. The track’s elevation is about 1,025 feet above sea-level. The current local measured weather conditions are 63.2° F, absolute pressure of 28.83 in Hg, and 58% relative humidity at 9 a.m. Note that when you have the current, measured absolute pressure, you do not need to enter the track elevation.

Calculate the Air Density Index (ADI) and density altitude for this example.


 0.

1. Enter current local measured weather conditions:

     TEMP S 63.2 °F

 (Absolute Pressure) P-ABS S 28.83 INHG

   (Moisture/Relative Humidity) RH% S 58. %

2. Calculate ADI and density altitude:







ELEV S 0.

ADI 94.641 %

D-ALT 1873.414 F

Recall that ADI is a ratio, expressed as a percentage, of the current air’s density to that of MSA. At the Auto Club Raceway under the aforementioned weather conditions, the air’s density is about 94.6% of that of MSA. Notice that the current air conditions at 1,025 feet above sea-level are theoretically the air conditions at an elevation of about 1,873 feet above sea-level.

In the next example, you are at the Firebird International Raceway, just outside of Phoenix, Ariz. The track’s elevation is about

1,082 feet above sea-level. The current local measured weather

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conditions are an unseasonably chilly 33° F, absolute pressure of

28.77 in Hg, and a relative humidity of 64% at 8:30 a.m.

Calculate the Air Density Index (ADI) and Density Altitude for this example.


 0.


   TEMP S 33. °F

 (Absolute Pressure) P-ABS S 28.77 INHG

  

(Moisture/Relative Humidity) RH% S 64. %

2. Calculate ADI and density altitude:







ELEV S 0.

ADI 101.002 %

D-ALT - 341.909 F

While these weather conditions at Firebird International Raceway are unlikely, this example demonstrates an ADI value of over 100% which is certainly a possible situation. As stated previously, air density is typically over 100% when temperatures are well below

60 °F.

Calculating ADI and Density Altitude

Using Elevation

For this example, you are at Top Gun Raceway in Fallon, Nev., and only have access to air temperature and humidity data.

However, you know the track’s elevation is about 3,963 feet above sea-level. With these three variables — air temperature, humidity, and elevation — you can still calculate ADI and Density

Altitude. The current weather conditions are posted as 51° F and

5% relative humidity at 9 a.m.

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Calculate the Air Density Index (ADI) and Density Altitude for this example.

First, clear the memory on your calculator, including temporary and semi-permanent entries.




1. Enter track elevation:

    

ALL CLEArEd

ELEV S 3963. F


  

 

TEMP S 51. °F

RH% S 5. %

3. Calculate ADI and Density Altitude:







ELEV S 3963. F

ADI 87.969 %

D-ALT 4323.207 F

Calculating and Using a

Fuel Correction Index

Note: In this example, it is assumed that your current air/ fuel settings and jet numbers are correct for your engine’s requirements at wide open throttle. This example uses a basic

Holley carburetor with squared jetting and identical primary and secondary main metering circuits. This example demonstrates how to compare a baseline ADI value to a new ADI value and the meaning of the difference between the two. In practice, this example can be used between ADI calculations at the same track throughout the day, or, between ADI calculations at two different tracks; the theory is the same.

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For this example, the current local measured weather conditions are 80° F, absolute pressure of 29.15 in Hg, and 53.5% relative humidity. Your race car ran best, under these baseline conditions, with #78 jets.

Calculate the Air Density Index (ADI).



 ALL CLEArEd


   TEMP S 80. °F

 (Absolute Pressure) P-ABS S 29.15 INHG

     (Moisture/Relative Humidity) RH% S 53.5 %

2. Calculate ADI:







ELEV S 0.

ADI 92.038 %

D-ALT 2813.209 F

Notice that the elevation output is 0 feet. This is because the example did not include entering an elevation. Elevation is only a required input if absolute pressure is not available. Record the calculated ADI of 92.038% and density altitude of about 2,813 feet in your log, along with your air/fuel settings and jet numbers. In this example, these are your baseline settings for this particular track location.

You are now at a different track location, and the current weather conditions have changed significantly. The air temperature is now

60° F, absolute pressure is 24.72 in Hg, and relative humidity is 39%.

Calculate the current ADI in order to determine if an adjustment is necessary.

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 0.

3. Enter current weather conditions:

   TEMP S 60. °F

 (Absolute Pressure) P-ABS S 24.72 INHG

   (Moisture/Relative Humidity) RH% S 39 %

4. Calculate ADI:







ELEV S 0.

ADI 81.94 %

D-ALT 6662.18 F

Record the calculated ADI of 81.94% and density altitude of 6,662 feet in your log.

5. Calculate a fuel correction index, which is simply the current

ADI of 81.94, divided by the baseline ADI of 92.038, then multiply by 100:

      

       

    89.028445

The fuel correction index is about 89%, indicating air density is about 89% of the air density from which you baselined your jet numbers. In other words, the new air density has gone down about

11% from your baseline air density calculation. Some experts say that as a general rule, a change of +/– 4% or more in air density is enough to consider a jetting change.

Also, notice that the density altitude at the new track location, about 6,662 feet, is much higher than the previous track’s density altitude of about 2,813. Typically, as density altitude goes up, you may require less fuel whereas if density altitude goes down, you may require more fuel.

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To translate a fuel correction index to a new jet number, recall your baseline was recorded with #78 jets, which according to the

Appendix B – Holley Jet Chart and Jet Orifice Area Conversion

Chart, have a flow of 645 cubic-centimeters per minute. Recall your fuel correction index is about 89%.

6. Calculate a new flow requirement:

        574.05

Using the chart in Appendix B, the closest flow number to 574 is the 566 cubic-centimeters per minute flow which corresponds to a #75 jet, which would be a change of three jet numbers down (in this example, density altitude has gone up so it stands to reason that a leaner jet number may be required). A conservative change, however, would be to go from the #78 to the #76 which has a flow of 587 cubic-centimeters per minute.

Calculating Water Vapor Content

Using a different set of track and weather conditions at Top

Gun Raceway, let’s calculate water vapor content (water vapor pressure, saturation water vapor pressure, and dew point).

The track’s elevation is about 3,963 feet above sea-level. The current local measured weather conditions are 73° F, absolute pressure of 25.88 in Hg, and 14% relative humidity at 10 a.m.


 0.

1. Enter current, local measured weather conditions:

   TEMP S 73. °F

 (Absolute Pressure) P-ABS S 25.88 INHG

   RH% S 14. %

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2. Calculate water vapor content by subsequent presses of :

 (Water Vapor Pressure) P-WV 0.115 INHG

 (Saturation Water Vapor Pressure) P-SAT 0.819 INHG

 (Dew Point) DEW 21.071 °F

Dew Point is a helpful temperature to know as it tells you approximately at what temperature you can expect to see moisture on the track surface. As you can see from the example above, the racers at Top Gun Raceway won’t need to worry about any dew on the track surface since it is extremely unlikely with those weather conditions for the temperature to reach 21 °F.

Repeated presses of [Moisture] will toggle back through the inputs and outputs, starting with the relative humidity input.

Basic ET Prediction

Note: Your calculator’s ET predictions may vary from other ET prediction sources primarily due to traction. The Hot Rod Calc assumes ideal conditions with no tire slippage and 100% converter lockup, and the predictions are for estimation purposes only.

Given your 1970 Ford Mustang Notchback, with a 411 HPproducing, stroked 351 CID engine, weighing in at about 3,840 pounds (including driver), calculate a simple elapsed time (ET) prediction. For a basic ET prediction, the calculator only requires vehicle weight and HP to be entered. The entered HP is assumed to be the engine’s rated HP in ideal or MSA conditions with no tire slippage and 100% converter lockup.

First, clear the memory on your calculator, including temporary and semi-permanent entries



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1. Enter vehicle weight (including driver):

    

2. Enter vehicle’s estimated rear wheel HP:

   

3. Calculate ET and MPH prediction:



















LBS S 3840

HP S MSA 411.

1/4ET 12.269 S

1/4 111.101 MPH

1/8ET 7.864 S

1/8 88.316 MPH

HPc 1.

P-ABS MSA 29.92 INHG

TEMP MSA 60. °F

RH% S 0. %

ELEV S 0.

Repeated presses of  will toggle back through the inputs and outputs, starting with the vehicle weight input.

ET Prediction and HPc

Note: This example assumes you have not cleared or reset the calculator after the previous Basic ET Prediction example. Your calculator’s ET predictions may vary from other ET prediction sources primarily due to traction. The Hot Rod Calc assumes ideal conditions with no tire slippage and 100% converter lockup, and the predictions are for estimation purposes only.

Building off of the previous Basic ET Prediction example, let’s zoom your 1970 Ford Mustang Notchback to Top Gun Raceway in

Fallon, Nev., and calculate an ET prediction using some additional inputs. The inputs demonstrated in this example are not required for an ET prediction, however, this example will demonstrate the

Hot Rod Calc’s ability to calculate a horsepower correction factor

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(HPc) and output for current weather conditions as well as MSA conditions.

For this example, the track’s elevation is 3,963 feet above sealevel. Recall that our race car weighs in at about 3,840 pounds, including the driver, and produces about 411 HP in ideal or MSA conditions. The current local measured weather conditions are 73°

F, absolute pressure of 25.88 in Hg, and 14% relative humidity.


1. We have already entered the vehicle’s weight and HP, so we can skip to the next input – local measured weather conditions:

   TEMP S 73. °F

 (Absolute Pressure) P-ABS S 25.88 INHG

   RH% S 14. %

2. Calculate ET and MPH prediction:



























1/4ET 13.045 S

1/4 104.491 MPH

1/4ET MSA 12.269 S

1/4 MSA 111.101 MPH

1/8ET 8.362 S

1/8 83.061 MPH

1/8ET MSA 7.864 S

1/8 MSA 88.316 MPH

HPc 1.202

P-ABS S 25.88 INHG

TEMP S 73. °F

RH% S 14. %

ELEV S 0.

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Notice within the ET output sequence, the ET predictions are displayed in 1/4 and 1/8 prediction sets based on current track conditions as well as a HPc of 1.202. Each set displays the horsepower corrected predictions (HPc) followed by the MSA adjusted predictions.

Repeated presses of  will toggle back through the inputs and outputs, starting with vehicle weight.

Display the entered MSA HP, corrected HP, and the calculated

Horsepower Correction Factor (HPc):








HP S MSA 411.

HP 341.92

HPc 1.202

Repeated presses of [HP] will toggle back through the inputs and outputs, starting with absolute pressure.

Note: Recall from the key definitions for Mechanical Efficiency

(ME%) that ME% is a numeric value representing a percentage of the power available inside the engine’s cylinders that makes its way to the flywheel (e.g., friction losses from rings, pistons, bearing friction, oil pumps, etc.). The default value is 85% which is a fairly acceptable value in practice. ME% is a variable in calculating the

HPc, and can be changed as in the following keystroke example.

Change the Mechanical Efficiency value from 85% to 80%.


   M-EFF S 80. %

To see the change to HPc, recall the HP value:






HP S MSA 411.

HP 339.44

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 HPc 1.211

Notice that by changing the ME% from 85% to 80% (reducing the engine’s mechanical efficiency), the corrected HP was reduced whereas the HPc was increased.

ET Prediction and Wind Conditions

Now let’s say you ran your 3,840-pound 1970 Ford Mustang

Notchback at Top Gun Raceway in Fallon, Nev., where there are often raging winds. You can use your actual ET and determine what your ET would have been without the windy conditions. You will need several new pieces of information. At a minimum, you need to know what the wind speed and direction were when the ET was recorded. Additionally, you need to know the race car’s frontal area and drag coefficient.

To determine your race car’s frontal area, measure the vehicle from “head-on”, measuring from the bottom of the front bumper to the top of the roof and the widest point to point of the race car (e.g. door handle to door handle). It is also helpful if you know your race car’s shape factor, though most are between 80% and 85% of the race car’s frontal area (excluding dragster style race cars).

Here’s an example of calculating a race car’s frontal area using a height of 46 inches, a width of 70 inches, and a shape factor of

85%.



   46

    3220

   

 

2737. S IN

19.006944 S F

The answer is about 19 square feet.

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Enter the estimated Frontal Area value:

 (Frontal Area) AREA S 19.006944 S F

Next, see Appendix A — Body Style and Drag Coefficients, for typical body styles and associated drag coefficient values.

The default Drag Coefficient value in the calculator is .35. Using

Appendix A for a “Notchback or Sedan” style body, we will select a value of .45.

Enter the Drag Coefficient of our 1970 Ford Mustang Notchback:


    (Drag Coefficient) DRAG S 0.45

Your disappointing ET was 13.85 at 102.304 MPH, and the vehicle weight is 3,840 pounds.

Note: A pure head-wind direction is entered as 0°; a pure crosswind direction is entered as 90°; a pure tail-wind direction is entered as 180°.

Head

0°

45°

90°

180°

Tail

At this point, the race car’s estimated Drag Coefficient and Frontal

Area entered and stored in memory.

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1. Next, enter vehicle weight, and your actual ET and MPH, the

Wind Speed, and if available, Wind Direction, to calculate how

the wind effected your speed and time:


    

     

       

  

(Wind speed)

  (Wind direction)

LBS S 3840.

ET S 13.85 S

SPEED S 102.304 MPH

WIND S 30. MPH

WIND° S 5. °

2. Calculate the corrected ET and MPH




 (Corrected ET)

 (Corrected Speed)

WIND S 30. MPH

ETc 13.281 S

SPDc 105.85 MPH

Repeated presses of  will toggle back through the inputs and outputs, starting with the Wind Speed input.

So, if you were to re-do your run, everything being the same except the wind conditions at the time of your recorded ET, you would run a 13.281 at 105.85 MPH.

Estimating Vehicle Weight

Often, a racer will try to figure out what a particular race car’s weight is or what Horsepower is required to achieve a recorded ET.

For this example, first clear the memory on your calculator, including temporary and semi-permanent entries.



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Your buddy has a 1978 Ford Mustang II with an estimated horsepower of 575 HP and made an ET run of 9.540 seconds.

Calculate the estimated Vehicle Weight.


1. Enter the estimated HP:

   

2. Enter the 1/4 ET:

     

3. Solve for the vehicle’s weight:



HP MSA S 575.

ET S 9.54 S

LBS 2525.953

In this example, your buddy has a 2005 Ford Mustang GT with an estimated horsepower of 520 HP and ran a 1/4 mile at 121.6 MPH.

Calculate the estimated Vehicle Weight.


4. Clear the memory first.



5. Enter the estimated HP:

   

6. Enter the speed at 1/4 mile:

     

7. Solve for the vehicle’s weight:



Estimating Rear Wheel Horsepower

0.

HP MSA S 520.

SPEED S 121.6 MPH

LBS 3705.529

In this example, your buddy has a 1973 Dodge Charger Rallye with an estimated vehicle weight of 4,280 pounds and made an ET run of 13.656 seconds. Calculate the estimated Horsepower.

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

1. Enter the estimated Vehicle Weight:

    

2. Enter the 1/4 ET:

      

0.

LBS S 4280.

ET S 13.656 S

3. Solve for the vehicle’s estimated rear wheel HP:

 HP MSA 332.17

Building from the prior example, let’s correct the estimated rear wheel HP based on current local measured weather conditions of

73° F, absolute pressure of 25.88 in Hg, and 14% relative humidity, then calculate the estimated Horsepower again.



   TEMP S 73. °F

 (Absolute Pressure) P-ABS S 25.88 INHG

   RH% S 14. %

5. There is no need to re-enter the Vehicle Weight or the 1/4 ET as they are currently in the calculator’s memory from the previous example.

6. Solve for the vehicle’s estimated MSA HP, Corrected HP, and

HPc:







HP MSA 399.281

HP 332.17

HPc 1.202

Repeated presses of  will toggle through the entered weather conditions, followed by the entered ET and Vehicle Weight.

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Calculating Effects of Changing Tire Sizes

Your daily commuter has four-wheel drive, and you want some extra ground clearance for those occasional off-highway excursions on the way home from work. However, before you make the switch to a taller tire, you want to know what the effects will be to your final-drive ratio and even more importantly, to your speedometer as you don’t want to draw any unnecessary attention while you are cruising down the highway.

In this example, your current tires are LT235/75R15’s. Your local tire store informed you that your current Sport Truck T/A tires have a diameter of 28.9 inches, whereas the mud tires you are looking to upgrade to have a tire diameter of 33 inches. Your four-wheeler currently has a final-drive ratio of 3.08.

Calculate the equivalent drive ratio (that is, the drive ratio that will provide you with similar performance and responsiveness) and the effect to your speedometer by going to a larger tire diameter.




1. Enter current final-drive ratio:



0.

GEAR S 3.08 RATIO

2. Enter old (current) and new tire diameters:

 (Old tire diameter) TIREo S 28.9 SIZE IN

 (New tire diameter) TIREn S 33. SIZE IN

3. Calculate the effect to your final-drive (D-EFF) and the equivalent final-drive (D-EQV):

TIRE 1.142 RATIO 

 (Final Drive Ratio)

 (Equivalent Drive Ratio)

D-EFF 2.697 RATIO

D-EQV 3.517 RATIO

Repeated presses of [Tire Ratio] will toggle through the inputs and

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outputs, starting with the current final-drive ratio input.

The effect to the final-drive (D-EFF) of going from a tire diameter of 28.9 to 33 inches is an estimated ratio of 2.697, which will create a fairly noticeable loss in your four-wheeler’s pickup from a stop or while rolling down the highway. To get back to a similar responsiveness on the new 33 inch diameter tires, you would want to install a set of final-drive gears closer to a 3.5 ratio (D-EQV).

Next, calculate the effect of the tire change to your speedometer.

You made the switch to the 33 inch tires, and you want to know what your actual speed will be with an indicated (gauge) speed of

65 MPH.

Don’t clear the memory on your calculator, we can use your inputs from the previous example which are currently in memory.

4. Enter a target indicated (gauge) speed of 65 MPH:

 SPEED S 65. MPH

5. Calculate the effect to speedometer:





 (Equivalent drive ratio)

 (Actual speed)

 (Gauge speed)



(Final drive ratio)

TIRE 1.142 RATIO

D-EFF 2.697 RATIO

D-EQV 3.517 RATIO

SPD►A 74.221 MPH

G►SPD 56.924 MPH

SPEED S 65. MPH

Repeated presses of [Tire Ratio] will toggle through the inputs and outputs, starting with the current final-drive ratio input.

For the entered indicated (gauge) speed on your speedometer of

65 mph, the actual speed is 74.221 mph (SPD ►A) after switching from 28.9 to 33 inch diameter tires. So, if you want to be going the legal 65 mph, you want your speedometer to read about 57 mph.

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Speed, RPM, Gear Ratios, and Tire Relationships

Speed, RPM, gear ratios, and tire sizes are interrelated, and with any three values, the fourth value can be solved on your calculator.

Getting these four areas set up properly on your road or drag strip vehicle can have very positive performance effects.

For the following examples, we will use a 1990 Ford Mustang

5.0 LX with a 5.0 liter V8 engine and the T-5, 5-speed manual overdrive transmission. The manual transmission ratios are 3.35 for 1st gear, 1.99 for 2nd, 1.32 for 3rd, direct drive 1.00 in 4th, and an overdrive 0.68 in 5th. The final-drive ratio is 3.08. Lastly, the tires have a diameter of 26 inches.

In this example, calculate your top speed in 2nd gear, assuming you are shifting at 5,500 RPM.




You will need to find the correct multiplier for 2nd gear. Recall that the final-drive ratio is 3.08 and 2nd gear is 1.99.

1. Multiply the final-drive ratio and 2nd gear ratio, and enter that as your Gear Ratio:

 GEAR S 6.1292 RATIO

2. Enter your shifting RPM and tire diameter:





RPM S 5500.

TIREn S 26. SIZE IN

3. Calculate the speed:

 SPEED 69.409 MPH

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Repeated presses of  will toggle through the inputs and outputs, starting with the gear ratio input.

From the above calculation, it is estimated that the mighty 5.0 LX will be going about 70 MPH at 5,500 RPM in 2nd gear.

In this example, calculate your RPM at 65 MPH in 5th gear:




You will need to find the correct multiplier for 5th gear. Recall that the final-drive ratio is 3.08 and 5th gear is 0.68.

0.

4. Multiply the final-drive ratio and 5th gear ratio, and enter that as your Gear Ratio:

 GEAR S 2.0944 RATIO

5. Enter your cruising speed of 65 MPH:

 SPEED S 65. MPH

6. Calculate the RPM:

 RPM 1760.004

Repeated presses of  will toggle through the inputs and outputs, starting with the gear ratio input.

From the above calculation, it is estimated that the 5.0 LX will be cruising at about 1,760 RPM while going down the highway at 65

MPH in overdrive, resulting in decent fuel mileage due to a low load on the 5.0 liter engine.

In this example, you want to solve for performance out on the highway. The 5.0 LX peaks in torque at about 3,000 RPM. When you want to downshift from 5th to 4th and safely overtake another car at the LX’s peak torque RPM, what final-drive ratio will enable the LX to reach 3,000 RPM at 65 MPH in 4th gear? Recall that 4th

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gear is direct drive and therefore would be the same as the finaldrive ratio you are solving for.


 0.

7. Enter your RPM, cruising speed of 65 MPH:





RPM S 3000.

SPEED S 65. M PH

8. Calculate the final-drive ratio:

 (Final-drive ratio)

 (Manual trans final-drive ratio)

 (Auto trans final-drive ratio)

GEAR 3.57 RATIO

GR-M 3.529 RATIO

GR-A 3.582 RATIO

Repeated presses of  will toggle through the inputs and outputs, starting with the RPM input.

From the above calculation, it is estimated that in order to reach

3,000 RPM in 4th gear at 65 MPH, the LX will need a final-drive ratio of 3.57. And for the users who have experience with the Larry

Shepard correction method, your calculator also shows a manual transmission (GR-M) final-drive ratio of 3.529 and an automatic transmission (GR-A) final-drive ratio of 3.582.

Instead of changing your final-drive ratio as in the previous example, you could have solved for the performance another way – by changing the tire size. Using the known parameters of 65 MPH,

3,000 RPM, and our current final-drive ratio of 3.08, calculate a new tire size that will give similar results as the final-drive ratio change in the previous example.




9. Enter your RPM, cruising speed of 65 MPH, and gear ratio:

0.

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





RPM S 3000.

SPEED S 65. M PH

GEAR S 3.08 RATIO

10. Calculate the New Tire Size:

 (New tire diameter) TIREn 22.431 SIZE IN

Repeated presses of  will toggle through the inputs and outputs, starting with the final-drive ratio input.

From the above calculation, it is estimated that in order to reach

3,000 RPM in 4th gear, at 65 MPH, the LX could utilize 22.4 inch diameter tires to achieve roughly the same performance as the previous example where you solved for a new final-drive ratio. It may not give you the look you like, but it would be a cost effective way to reach your goal. Just remember, by changing the tire size, your speedometer will be effected (see Calculating Effects of

Changing Tire Sizes for more information).

Calculating Carburetor Size

The Hot Rod Calc can calculate carburetor sizes in four configurations based on different volumetric efficiency (VE) values:

User, Theoretical, Street, and Race. See Calculating Volumetric

Efficiency for more about VE.

The User carburetor size configuration utilizes a user-entered VE value, whereas Theoretical uses a predefined VE value of 100%,

Street uses a VE value of 85%, and Race uses a VE value 110%.

When calculating the carburetor size for your application, be careful about what RPM you enter. Selecting an overstated/ unrealistic RPM for your engine at wide open throttle (WOT) will result in a mathematically valid carburetor size, but will likely not work well with your application. It is best to consult your vehicle’s manual or an expert regarding the WOT maximum engine RPM for your vehicle.

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Lastly, while carburetors come in many sizes, they are not available in just any size. It is quite possible you won’t find one that is of the exact size you calculated on your Hot Rod Calc.

Carburetor sizes are designated by airflow capacity in cubic-feet per minute (CFM).

In this example, you want to upgrade your 1968 Pontiac GTO’s carburetor. With all the engine and accessory modifications you have made, your Ram Air II 400 CID engine makes its peak horsepower RPM at about 5400 RPM. Calculate the Theoretical,

Street, and Race carburetor sizes.


 0.

1. Enter your RPM and engine displacement:





RPM S 5400.

ENG S SIZE 400. CU IN

2. Calculate the carburetor sizes:







THEOR CARB SIZE 625. CFM

STREET CARB SIZE 531.25 CFM

RACE CARB SIZE 687.5 CFM

The theoretical carburetor size of about 625-cfm was calculated based on the theoretical air capacity at the entered RPM and engine size (100% theoretical capacity). In this example, you want to upgrade to an application that leverages your modifications, the race carb size of about 688-cfm might be your answer (calculated at 110% of theoretical capacity). However, it is unlikely that you will find a carburetor in the exact calculated size so you might have only a couple options in a reasonable range such as a 650-cfm or a 750-cfm carburetor size.

Notice that a User carburetor size is not included in this example.

This is because a known VE was not entered into the calculator.

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Calculating Carburetor Size

With a Known Volumetric Efficiency

Building off of the previous example, you want to calculate your userdefined carburetor size based on a known VE value. Suppose through your experience and knowledge of your 1968 Pontiac GTO’s engine specs and modifications, you know you can reach a VE of 95%.


1. Calculate a carburetor size based on a user-specified VE. Your

RPM and engine displacement are in memory, so you need to only add your user-specified VE of 95%:

 EFF% S 95. VOL %

2. Calculate the carburetor sizes:









USER CARB SIZE 593.75 CFM

THEOR CARB SIZE 625. CFM

STREET CARB SIZE 531.25 CFM

RACE CARB SIZE 687.5 CFM

Notice within the  outputs, the User carburetor size appears first in the output. This carburetor size is calculated using the entered VE value of 95%. As previously mentioned, you are not likely to find an exact size of 594-cfm.

Repeated presses of  will toggle back through the inputs and outputs, starting with the VE input.

Calculating Volumetric Efficiency

Volumetric Efficiency (VE) is the actual measured airflow capacity at a particular RPM divided by the theoretical airflow capacity at the same RPM. VE is generally expressed as a percentage. To calculate the VE of your vehicle, you need to know a few things.

First, you need to know your actual measured airflow capacity at maximum speed or maximum torque (a local dyno shop can help

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you with this if they have an air-flow meter), as well as your engine displacement.

In this example, your 1968 Pontiac GTO has a Ram Air II 400 CID engine and you want to calculate the engine’s VE at 7000 RPM which is the RPM at your maximum speed. Your measured airflow capacity at 7000 RPM is said to be 625-cfm.


 0.

1. Enter your RPM, engine displacement, and actual measured airflow capacity at 7000 RPM :







RPM S 7000.

ENG S SIZE 400. CU IN

USER S CARB SIZE 625. CFM

2. Calculate your engine’s VE:

 EFF% 77.143 VOL %

The calculated VE of your GTO, at 7000 RPM, is about 77%. This value is just under 80%, which for many typical street applications is on track.

Estimating Flywheel Horsepower at a Known RPM

If you know torque output at a specific RPM, you can calculate horsepower at that same RPM.

In this example, your 400 CID engine produces 445 pounds-feet of torque at 3800 RPM. Calculate flywheel horsepower for the same

RPM.


 0.

 LB-FT S MSA 445.

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 RPM S 3800.

2. Calculate the HP at 3800 RPM:

 HP MSA 321.966

At 3800 RPM, when your 400 CID engine is producing 445 pounds-feet of torque, it is also producing about 322 HP at the flywheel.

Estimating Flywheel Torque at a Known RPM

If you know horsepower output at a specific RPM, you can calculate torque at that same RPM.

In this example, your 400 CID engine produces 366 HP at 5400

RPM. Calculate the torque for the same RPM.


 0.

1. Enter your HP and RPM:





HP S MSA 366.

RPM S 5400.

2. Calculate the Torque at 5400 RPM:

 LB-FT MSA 355.977

At 5400 RPM, when your 400 CID engine is producing 366 HP, it is also producing about 356 pounds-feet of torque at the flywheel.

Calculating Compression Ratio

Compression ratio is the relationship between cylinder volume with the piston at bottom dead center (BDC) to cylinder volume with the piston at top dead center (TDC).

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TDC BDC

There are several compression ratio effects to consider when determining the appropriate ratio for your application:

• The greater the compression ratio, the greater the amount of air/ fuel mix will be compressed.

• The greater amount of air/fuel mix that is compressed, the greater the combustion power will be.

• The greater the combustion power is, the hotter the combustion is which can lead to detonation.

• Detonation (pinging and knocking) can be resolved by using higher octane fuel (at a higher cost, of course) and/or a change in ignition timing curve.

So, to get big power, you need big compression ratios to get more powerful combustion, which requires higher octane fuels.

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Your Hot Rod Calc needs several inputs to calculate a

Compression Ratio, but you will need track them down and in some cases, measure manually:

• Bore and Stroke – You should be able to find this in your engine repair manual.

• Head Gasket Bore and Thickness – You should be able to measure or get Head Gasket Bore and Thickness from the gasket manufacturer.

• Deck Height – You should be able to measure this manually.

• Piston Dome Volume – You can measure this, or the piston manufacturer likely can tell you the valve relief volume. Domed piston volumes should be expressed as a negative number (also, domed pistons take away from the chamber volume and as such, raise compression), whereas dished piston volumes should be entered as a positive number (they add to the chamber volume, and have a lowering effect on compression).

• Cylinder Head Combustion Chamber Volume – You will need to measure this manually.

Note: Your Hot Rod Calc user’s guide does not go into details on measuring Piston Dome Volume or Combustion Chamber Volume.

You will need to consult an auto repair or engine building resource for that procedure.

For this example, you have a typical Chevrolet 350 CID engine.

Your known Bore and Stroke are 4 inches and 3.48 inches, respectively and you measured your Combustion Chamber Volume at 76 cubic-centimeters. From your gaskets, you find that your

Head Gasket Bore is 4.100 inches and Head Gasket Thickness is

.038 inches. Your Deck Height is .015 inches (distance from top of piston at top dead center to the block deck surface). Your piston manufacturer informed you that your dished valve reliefs are 4.5 cubic-centimeters.

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 0.

1. Enter the values from the example:





BORE S 4. IN

STROK S 3.48 IN

 (Gasket Bore) G-BOR S 4.1 IN

 (Gasket Thickness) G-THK S 0.038 IN

 (Deck Height) DECK S 0.015 IN

 (Dome Volume) DOME S 4.5 VOL CC

 (Chamber Volume) CHMBR S 76 VOL CC

2. Calculate the Compression Ratio:

 COMP 8.805 RATIO

Repeated presses of  will toggle through the inputs and outputs, starting with the entered Bore.

The calculated compression ratio is about 8.81:1. At this point, if you were not satisfied with this ratio, you can use your Hot Rod

Calc to play out some other scenarios.

For this example, to raise your compression ratio, you could enter a thinner Head Gasket Thickness of 0.015. All the other inputs are in your calculator’s memory.


3. Change the Gasket Thickness by entering .015 inches:

 G-THK S 0.015 IN

4. Re-calculate the Compression Ratio:

 COMP 9.253 RATIO

Notice the increase in the calculated compression ratio. In summary, lowering the overall chamber volume will increase the

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compression ratio, whereas raising the overall chamber volume will decrease the compression ratio. Piston Dome, Deck Height, and Head Gasket Thickness are several ways to effect your compression ratio. In the next section, you can read about one of the more popular ways to increase compression ratio, which is a process known as milling.

Calculating Mill Amount

Another method of increasing the compression ratio on your engine is to mill, or remove material from, the heads. Generally, you will have a target compression ratio you want to achieve and you want to determine how much material to remove from your engine’s heads.

Note: Your Hot Rod Calc user’s guide does not go into details on the milling process. Your local engine building shop will likely have the necessary knowledge and tools for milling your heads to your specs.

For this example, you want to increase your compression ratio from

8.5:1 (current Compression Ratio) to 10.5:1. Your Stroke is 3.84 inches. The following keystrokes will show you how to calculate the amount to mill:


 0.

1. Enter your Stroke and current Compression Ratio:





STROK S 3.48 IN

COMP S 8.5 RATIO

2. Enter your target Compression Ratio, and calculate the Mill

Amount:

 MILL 0.098 IN

Repeated presses of  will toggle through the inputs and outputs,

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starting with the entered Stroke.

To raise your compression from 8.5:1 to 10.5:1, your engine building shop would need to remove 0.098 inches of material from the surface of your heads, thus reducing the overall chamber volume and increasing compression.

Notice the answer to your mill amount question is given in inches, 0.098 inches, but it’s a simple press of a key to convert to millimeters if necessary. If you press the  key, your calculated mill amount of 0.098 inches is converted to about 2.48 millimeters.

Calculating Piston Speed

Piston speed is an important factor when building an engine, especially if that engine is being built to run short distances at wide open throttle such as drag racing. Piston speed is the speed, typically in feet per minute, at which the piston moves up and down within a cylinder.

As your engine’s crankshaft rotates once, your cylinder’s piston travels two strokes (up one, and down one). The piston’s speed is not constant throughout its travel. It may go from 0 to 100 miles per hour and back to 0 during a single stroke. However, if the piston speed is too fast, the result can be disastrous for your engine.

With advanced math, you could calculate the exact piston speed at any particular point in the crankshaft rotation. Fortunately, knowing the average piston speed is all you need to calculate when you are building your engine. Modern metal materials enable higher piston speeds today, upwards of 3500 feet per minute.

For this example, your Stroke is 3.48 inches, and you want to calculate the Piston Speed at 4000 RPM.


 0.

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1. Enter your Stroke and the RPM for which you want to determine piston speed:





STROK S 3.48 IN

RPM S 4000.

2. Calculate the Piston Speed at 4000 RPM:

 FPM

 M/MIN 707.136

Repeated presses of [Piston Speed] will toggle through the inputs and outputs, starting with the entered Stroke.

At 4000 RPM, that is a piston speed of 2,560 feet per minute or about 707.1 meters per minute. What about at 5000 RPM?

3. Enter the RPM for which you want to determine piston speed:

 RPM S 5000.

4. Calculate the Piston Speed at 5000 RPM :

 FPM

 M/MIN

At 5000 RPM, your piston speed is 2,900 feet per minute and is pushing the edge of what modern metal materials can handle, even in short durations.

Your Hot Rod Calc can also calculate an RPM limit should you want to calculate a limit based on a particular piston speed.

Calculate an RPM with a Piston Speed of 3500 feet per minute and a Stroke of 3.48 inches.


5. Clear your calculator:

 0.

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6. Enter the Piston Speed for which you want to determine an RPM limit, along with stroke of 3.48:





FPM S 3500.

STROK S 3.48 IN

7. Calculate the RPM limit:

 RPM 6034.483

Calculating Engine Displacement

You could simply check the factory specs on the engine displacement of your vehicle, but that number is usually a rounded up or down number. If you are building an engine to your specification, or modifying one and want to know the effects on displacement by changing bore and/or stroke, the Hot Rod Calc can do it.

In this example, your 1968 Pontiac GTO’s Ram Air II engine has a published engine displacement of 400 CID. The spec bore and stroke are 4.12 inches and 3.75 inches, respectively. Calculate the exact cubic-inch displacement. Your calculator defaults to 8 cylinders.




1. Enter your Bore and Stroke:





0.

BORE S 4.12 IN

STROKE S 3.75 IN

2. Calculate the actual Engine Displacement:









ENG SIZE 399.95 CU IN

ENG SIZE 6554.004 CC

ENG SIZE 6.554 L

CYL VOL 49.994 CU IN

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Repeated presses of  will toggle through the inputs and outputs, starting with the entered Bore.

While the exact displacement of the 1968 Ram Air II engine is about 399.95 CID, it’s a tough number to market by the factory.

To make it simple on the guys in the suits, the displacement was rounded up to a nice even 400 CID. Notice the engine displacement is also displayed in cubic-centimeters and liters, and lastly the cylinder volume is calculated and displayed in cubicinches.

In this example, your 1962 Ford Falcon straight-6 engine has a published engine displacement of 169.95 CID. The spec Bore and

Stroke are 3.5 inches and 2.94 inches, respectively. Calculate the exact cubic-inch displacement by going to a larger Bore of 3.75.

Your calculator defaults to 8 cylinders, and since the 1962 Ford

Falcon only has 6 cylinders, you will need to change the number of cylinders to 6.


 0.

3. Change from 8 to 6 cylinders:

 QTY S 6.

4. Enter your Bore and Stroke:





BORE S 3.75 IN


5. Calculate the actual Engine Displacement:









ENG SIZE 194.828 CU IN

ENG SIZE 3192.656 CC

ENG SIZE 3.193 L

CYL VOL 32.471 CU IN

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Repeated presses of  will toggle through the inputs and outputs, starting with the entered Bore.

Calculating Bore and Stroke

Building from one of the previous examples, you want to push your cubic inch displacement to a maximum of 405 CID to be competitive at your local club races as well as meet class engine requirements. Recall that the stock bore and stroke on the 1968

Ram Air II engine is 4.12 and 3.75 inches, respectively. Keeping the stock Stroke length, calculate a new Bore size.




1. Enter the target displacement of 405 CID and current Stroke length:





ENG S SIZE 405 CU IN


2. Calculate the new Bore:

 BORE 4.146 IN

In order to be within your class requirements, you could go to an over-bored size of 4.146 inches.

3. Next, go the other way. Keeping your stock Bore, solve for a longer Stroke length. Enter your stock Bore of 4.12 inches, and a target displacement of 405 CID.







0.

BORE S 4.12 IN

ENG S SIZE 405 CU IN

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4. Calculate the new Stroke length:

 STROK 3.797 IN

Notice you can also meet your goals by keeping the stock bore, and going to a longer stroke of 3.797. In terms of cost, it will be more cost effective to go over bore to reach your goals in this particular example.

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APPENDIX A –

BODY STYLE AND DRAG COEFFICIENTS*

BODY STYLE DRAG COEFFICIENT

Open Convertible

Station Wagon and Van Body

Notchback or Sedan

0.5 – 0.7

0.5 – 0.6

0.4 – 0.55

Fastback

Fairings all around, streamlined shape

0.3 – 0.4

0.2 – 0.25

K-shape 0.23

Optimum streamliner

Motorcycles

Trucks

Buses

0.15 – 0.2

0.6 – 0.7

0.8 – 1.5

0.6 – 0.7

* Aerodynamic drag data from Bosch Automotive Handbook

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APPENDIX B –

HOLLEY JET CHART AND

JET ORIFICE AREA AND CONVERSION CHART

Main Jet Number, Drill Size, and Flow

JET NO. DRILL SIZE FLOW

4 0 .040 117

41 .041 122

42 .042 129

43 .043 135

44 .044 142

45 .045 149

46 .046 156

47 .047 163

48 .048 170

49 .049 178

50 .049 185

51 .050 194

52 .052 203

53 .052 212

54 .053 221

55 .054 230

56 .055 240

57 .056 251

58 .057 262

59 .058 273

60 .060 285

61 .060 298

62 .061 311

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63 .062 325

64 .064 341

65 .065 357

66 .066 374

67 .068 392

68 .069 411

69 .070 429

70 .073 448

71 .076 470

72 .079 492

73 .079 517

74 .081 542

75 .082 566

76 .084 587

77 .086 615

78 .089 645

79 .091 677

80 .093 703

81 .093 731

82 .093 765

83 .094 795

84 .099 824

85 .100 858

86 .101 890

87 .103 923

88 .104 952

89 .104 987

90 .104 1014

91 .105 1080

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92 .105 1150

93 .105 1200

94 .108 1260

95 .118 1320

96 .118 1375

97 .125 1440

98 .125 1500

99 .125 1570

100 .128 1640

.

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Jet Orifice Area Conversion

Jet

Size

Dia.

(")

Jet

Size

Area

(sq. ")

Jet

Size

Dia.

(")

Jet

Size

Area

(sq. ")

Jet

Size

Dia.

(")

Jet

Size

Area

(sq. ")

Jet

Size

Dia.

(")

Jet

Size

Area

(sq. ")

Jet

Size

Dia.

(")

Jet

Size

Area

(sq. ")

Jet

Size

Dia.

(")

Jet

Size

Area

(sq. ")

0.02 0.00031 0.049 0.00189 0.078 0.00478 0.107 0.00899 0.136 0.01453 0.164 0.02112

0.021 0.00035 0.05 0.00196 0.079 0.0049 0.108 0.00916 0.137 0.01474 0.165 0.02138

0.022 0.00038 0.051 0.00204 0.08 0.00503 0.109 0.00933 0.138 0.01496 0.166 0.02164

0.023 0.00042 0.052 0.00212 0.081 0.00515 0.11 0.0095 0.139 0.01518 0.167 0.0219

0.024 0.00045 0.053 0.00221 0.082 0.00528 0.111 0.00968 0.14 0.01539 0.168 0.02217

0.025 0.00049 0.054 0.00229 0.083 0.00541 0.112 0.00985 0.141 0.01562 0.169 0.02243

0.026 0.00053 0.055 0.00238 0.084 0.00554 0.113 0.01003 0.142 0.01584 0.17 0.0227

0.027 0.00057 0.056 0.00246 0.085 0.00568 0.114 0.01021 0.143 0.01606 0.171 0.02297

0.028 0.00062 0.057 0.00255 0.086 0.00581 0.115 0.01039 0.144 0.01628 0.172 0.02324

0.029 0.00066 0.058 0.00264 0.087 0.00595 0.116 0.01057 0.145 0.01651 0.173 0.02351

0.03 0.00071 0.059 0.00273 0.088 0.00608 0.117 0.01075 0.146 0.01674 0.174 0.02378

0.031 0.00076 0.06 0.00283 0.089 0.00622 0.118 0.01094 0.147 0.01697 0.175 0.02405

0.032 0.0008 0.061 0.00292 0.09 0.00636 0.119 0.01112 0.148 0.0172 0.176 0.02433

0.033 0.00086 0.062 0.00302 0.091 0.0065 0.12 0.01131 0.149 0.01744 0.177 0.02461

0.034 0.00091 0.063 0.00312 0.092 0.00665 0.121 0.0115 0.15 0.01767 0.178 0.02489

0.035 0.00096 0.064 0.00322 0.093 0.00679 0.122 0.01169 0.151 0.01791 0.179 0.02517

0.036 0.00102 0.065 0.00332 0.094 0.00694 0.123 0.01188 0.152 0.01815 0.18 0.02545

0.037 0.00108 0.066 0.00342 0.095 0.00709 0.124 0.01208 0.153 0.01839 0.181 0.02573

0.038 0.00113 0.067 0.00353 0.096 0.00724 0.125 0.01227 0.154 0.01863 0.182 0.02602

0.039 0.0012 0.068 0.00363 0.097 0.00739 0.126 0.01247 0.155 0.01887 0.183 0.0263

0.04 0.00126 0.069 0.00374 0.098 0.00754 0.127 0.01267 0.156 0.01911 0.184 0.02659

0.041 0.00132 0.07 0.00385 0.099 0.0077 0.128 0.01287 0.157 0.01936 0.185 0.02688

0.042 0.00139 0.071 0.00396 0.1 0.00785 0.129 0.01307 0.158 0.01961 0.186 0.02717

0.043 0.00145 0.072 0.00407 0.101 0.00801 0.13 0.01317 0.159 0.01986 0.187 0.02747

0.044 0.00152 0.073 0.00419 0.102 0.00817 0.131 0.01348 0.16 0.02011 0.188 0.02776

0.045 0.00159 0.074 0.0043 0.103 0.00833 0.132 0.01369 0.161 0.02036 0.189 0.02806

0.046 0.00166 0.075 0.00442 0.104 0.00846 0.133 0.01389 0.162 0.02061 0.19 0.02835

0.047 0.00174 0.076 0.00454 0.105 0.00866 0.134 0.0141 0.163 0.02087 0.191 0.02865

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APPENDIX C –

Default Settings

After a Clear All (  ) your calculator will return to the following settings:

STORED VALUES DEFAULT VALUE

Air Temperature

Absolute Pressure

Moisture

Elevation

ADI

Density Altitude

Drag Coefficient

Mechanical Efficiency

#Cylinders

Volumetric Efficiency

60.0 °F

29.92 in Hg

0% RH

0 FEET

100%

– 0.001 FEET

0.35

85%

8

100%

If you replace your batteries or perform a Full Reset*, press  , hold down  , and press  . your calculator will return to the following settings (in addition to those listed above):

Preference Settings DEFAULT VALUE

Functional Rounding

Default Unit Format

Meter Rounding

F-RND 0.000

US UNITS

METER 0.000

*Depressing the Reset button located above the  key will also perform a Full Reset.

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APPENDIX D –

Care Instructions

Please follow the guidelines listed in this section for proper care and operation of your calculator. Not following the instructions listed below may result in damage not covered by your warranty. Refer to the Repair and Return section on page 44 for more details.

Do not expose calculator to temperatures outside the operating temperature range of 32ºF – 104ºF (0ºC – 40ºC).

Do not expose calculator to high moisture such as submersion in water, heavy rain, etc.

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APPENDIX E –

Accuracy/Errors, Auto Shut-Off, Batteries, Reset

ACCURACY/ERRORS

Accuracy/Display Capacity — Your calculator has an eightdigit display made up of eight digits.

Errors — When an incorrect entry is made, or the answer is beyond the range of the calculator, it will display the word

“ ERROR.” To clear an error condition you must hit the  button once. At this point you must determine what caused the error and re-key the problem.

ERROR CODES

OFLO Overflow (too large)

MATH Error Divide by 0

ENT Error Invalid entry error

Auto-Range — If an “overflow” is created because of an input and calculation with small units that are out of the standard seven-digit range of the display, the answer will be automatically expressed in the next larger units (instead of showing “ ERROR”) — e.g., 20,000,000 mm is shown as 20,000 m. Also applies to inches and feet.

AUTO SHUT-OFF

Your calculator is designed to shut itself off after about 8-12 minutes of non-use.

BATTERIES

The Hot Rod Calc uses two LR-44 batteries.

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Replacing Batteries

Should your calculator display become very dim or erratic, replace the batteries.

Note: Please use caution when disposing of your old battery, as it contains hazardous chemicals.

Replacement batteries are available at most discount or electronics stores. You may also call Calculated Industries at

1-775-885-4900.

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WARRANTY, REPAIR AND RETURN INFORMATION

Return Guidelines

1. Please read the Warranty in this User’s Guide to determine if your Calculated Industries product remains under warranty before calling or returning any device for evaluation or repairs.

2. If your product won’t turn on, check the batteries as outlined in the User’s Guide.

3. If you need more assistance, please go to the website listed below.

4. If you believe you need to return your product, please call a Calculated Industries representative between the hours of 8:00am to 4:00pm Pacific Time for additional information and a Return Merchandise Authorization (RMA).

Call Toll Free: 1-800-854-8075

Outside USA: 1-775-885-4900 www.calculated.com/warranty

WARRANTY

Warranty Repair Service – U.S.A.

Calculated Industries (“CI”) warrants this product against defects in materials and workmanship for a period of one (1) year from the

date of original consumer purchase in the U.S. If a defect exists during the warranty period, CI at its option will either repair (using new or remanufactured parts) or replace (with a new or remanufactured calculator) the product at no charge.

THE WARRANTY

WILL NOT APPLY TO THE PRODUCT IF IT HAS

BEEN DAMAGED BY MISUSE, ALTERATION, ACCIDENT, IMPROPER

HANDLING OR OPERATION, OR IF UNAUTHORIZED REPAIRS

ARE ATTEMPTED OR MADE. SOME EXAMPLES OF DAMAGES

NOT COVERED BY WARRANTY INCLUDE, BUT ARE NOT LIMITED

TO, BATTERY LEAKAGE, BENDING, A BLACK “INK SPOT” OR

VISIBLE CRACKING OF THE LCD, WHICH ARE PRESUMED TO BE

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DAMAGES RESULTING FROM MISUSE OR ABUSE.

To obtain warranty service in the U.S., please go to the website.

A repaired or replacement product assumes the remaining warranty of the original product or 90 days, whichever is longer.

Non-Warranty Repair Service – U.S.A.

Non-warranty repair covers service beyond the warranty period, or service requested due to damage resulting from misuse or abuse.

Contact Calculated Industries at the number listed above to obtain current product repair information and charges. Repairs are guaranteed for 90 days.

Repair Service – Outside the U.S.A.

To obtain warranty or non-warranty repair service for goods purchased outside the U.S., contact the dealer through which you initially purchased the product. If you cannot reasonably have the product repaired in your area, you may contact CI to obtain current product repair information and charges, including freight and duties.

Disclaimer

CI MAKES NO WARRANTY OR REPRESENTATION, EITHER

EXPRESS OR IMPLIED, WITH RESPECT TO THE PRODUCT’S

QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS

FOR A PARTICULAR PURPOSE. AS A RESULT, THIS PRODUCT,

INCLUDING BUT NOT LIMITED TO, KEYSTROKE PROCEDURES,

MATHEMATICAL ACCURACY AND PREPROGRAMMED

MATERIAL, IS SOLD “AS IS,” AND YOU THE PURCHASER

ASSUME THE ENTIRE RISK AS TO ITS QUALITY AND

PERFORMANCE.

IN NO EVENT WILL CI BE LIABLE FOR DIRECT, INDIRECT,

SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES

RESULTING FROM ANY DEFECT IN THE PRODUCT OR ITS

DOCUMENTATION.

The warranty, disclaimer, and remedies set forth above are exclusive and replace all others, oral or written, expressed or implied. No CI dealer, agent, or employee is authorized to make any modification, extension, or addition to this warranty.

Some states do not allow the exclusion or limitation of implied warranties or liability for incidental or consequential damages, so the above limitation or exclusion may not apply to you. This warranty gives you specific rights, and you may also have other rights, which vary from state to state.

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FCC Class B

This equipment has been certified to comply with the limits for a Class

B calculating device, pursuant to Subpart J of Part 15 of FCC rules.

Legal Notes

Software copyrighted and licensed to Calculated Industries by

Specialty Calculator Technologies, LLC, 2009.

User’s Guide copyrighted by Calculated Industries, Inc., 2009.

Hot Rod Calc™ is trademarked and Calculated Industries® is a registered trademark of Calculated Industries, Inc.

ALL RIGHTS RESERVED

Designed in the U.S.A.

Looking For New Ideas

Calculated Industries, a leading manufacturer of special-function calculators and digital measuring instruments, is always looking for new product ideas in these areas.

If you have an idea, or a suggestion for improving this product or

User’s Guide, please submit your comments online at: www.

calculated.com under “Contact Us”, “Product Idea Submittal

Agreement”. Thank you.

4840 Hytech Drive

Carson City, NV 89706 U.S.A.

1-800-854-8075 • Fax: 1-775-885-4949

E-mail: [email protected]

www.calculated.com

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FCC Class B

This equipment has been certified to comply with the limits for a Class

B calculating device, pursuant to Subpart J of Part 15 of FCC rules.

Legal Notes

Software copyrighted and licensed to Calculated Industries by

Specialty Calculator Technologies, LLC, 2009.

User’s Guide copyrighted by Calculated Industries, Inc., 2009.

Hot Rod Calc™ is trademarked and Calculated Industries® is a registered trademark of Calculated Industries, Inc.

ALL RIGHTS RESERVED

Designed in the U.S.A.

Looking For New Ideas

Calculated Industries, a leading manufacturer of special-function calculators and digital measuring instruments, is always looking for new product ideas in these areas.

If you have an idea, or a suggestion for improving this product or

User’s Guide, please submit your comments online at: www.

calculated.com under “Contact Us”, “Product Idea Submittal

Agreement”. Thank you.

4840 Hytech Drive

Carson City, NV 89706 U.S.A.

1-800-854-8075 • Fax: 1-775-885-4949

E-mail: [email protected]

www.calculated.com

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OT

R

OD

C

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