Speed Gearing & RPM Calculator

[enigmas]

At some time in the near future I'll be updating the engine and transmission in my mechanically modified Mk3 P5 Coupe.
I have a rebuilt P76 4.4 litre V8 engine on a stand that will be hooked up to a Jaguar XJ40 ZF4HP22 transmission.
This will replace the existing P76 V8 and BW35 in the car.

As the ZF transmission has 4th gear as an overdrive ratio (.73) I need to know how fast the engine is spinning at a particular road speed.
To obtain the engine rpm at say 70 mph a few specific details need to be known.

These are:

1. MPH (Choose a viable highway speed for your car)

2. Axle ratio/Rear Gear Ratio (P5B & Mk3 diff ratio = 3.5) (other P5s 3.9?)

3. Transmission ratio (BW35. Use 1) (ZF trans JagXJ40 Use .73)

4. Transfer case ratio (If 4 wheel Drive) (Use 1 if two whee drive)

5. Tire Diameter (measure on car. Use Imperial measurement.

NOTE: THIS WILL WORK FOR ANY VEHICLE.

The link below will take you to the calculator at "Currie Enterprises".
This is only one of several of their calculators.

* There are 2 pictures below of their RPM calculator.
* The figures in the "field boxes" relate to my car when fitted with the ZF transmission.
* The ZF trans has an overdrive ratio of .73
* The BW35 3 speed trans has direct drive in 3rd. Use the number 1 in the field.
* Note: For the "Transfer Case" field...input the number 1 (For a 2 wheel drive car)



This second image illustrates the difference in RPM at 70 mph with the BW35 transmission.
The BW35 has only 3 speeds and no overdrive ratio.
The input field number is 1.



Here is the link below to the "Currie Enterprises RPM Calculator"
With it you can easily calculate how fast the engine in your model P5 is revving for a particular road speed.
Simply input the data listed above.
All figures are Imperial.


www.curriecalculators.com/rpmCalculator.htm

[enigmas]

No views or opinions on the calculator guys?

I thought it would be a useful tool as it applies to any car but allows an accurate determination of how fast the engine in your P5 or P5B is turning-over (RPM) based essentially on what tyre size (diameter) are fitted and the car's final drive ratio.

Simply pick your highway cruising speed (mph) input the 5 criteria into the field boxes, click calculate and you have the answer.

[Phil Nottingham]

It is useful so made it a STICKY