Ford CMP axle ratios?

[Hanno Spoelstra]

Not having my abacus on hand, I used an online calculator (http://www.advanced-ev.com/Calculators/TireSize/) to calculate the following:

Both trucks traveling at convoy speed of 25 mph:

F30 with 7.16 diff ratio and 37" diameter (10.50-16) tyre: engine runs at 1626 rpm

F60L/FGT with 7.16 diff ratio and 41" diameter (10.50-20) tyre: engine runs at 1467 rpm

Pretty much the same? A heavier (loaded) truck would of course use more fuel.

Still some homework to be done. Grant, does the AEDB list 9.00-16 tyre diameters so we can compute F15 and F15A engine rpm @ 25 mph?

[Tony Smith]

Originally Posted by Hanno Spoelstra

Not having my abacus on hand, I used an online calculator (http://www.advanced-ev.com/Calculators/TireSize/) to calculate the following:

Both trucks traveling at convoy speed of 25 mph:

F30 with 7.16 diff ratio and 37" diameter (10.50-16) tyre: engine runs at 1626 rpm

F60L/FGT with 7.16 diff ratio and 41" diameter (10.50-20) tyre: engine runs at 1467 rpm

Pretty much the same?

Not even close. The 10% difference in revs results in a loss of nearly 20% of the power. My copy of the Ford Service bulletins is missing the Power/torque curve for the 1939-on 239ci 95hp engine ( ), but I have attached the pic of the 85hp to demonstrate.

At 1467rpm, the 85hp engine is producing about 38hp and about 151ft.lb of torque. At 1626rpm, those figures jump to 45hp and 155ft.lb.

I have found a chart online for the 95hp which seems to show corresponding figures of 42hp /160ft.lb at 1467rpm and 53hp/164ft.lb at 1626rpm. Clearly the 60cwt will be struggling carrying twice the load.

Using your linked calculator, if the 60cwt is in 3rd gear (1.69:1 x 7.16 = 12.1), at 25mph the engine will be turning 2479rpm. At these revs, the 95hp will be producing 81hp and 161ft.lb., or nearly 60% more power than the 30cwt in 4th gear.

The Ford V8 loves to rev, and that's how the 60cwt will be capable of carrying twice the load at the same road speed as the 30cwt. The Chev engines however, have a reputation of producing more power and torque lower in the rev range, and their comparative power outputs at certain revs WILL be different to the Ford. This trait of the Chev engine will see them shifting up a gear sooner than the Ford V8, which prefers to rev out fully in a gear before shifting up. Interestingly, the Ford 226 Straight6 in the 2GT trucks (has a very similar torque curve to the Chev 216, and would be a more compatible truck in Convoy with the Chev).

[Grant Bowker]

Originally Posted by Hanno Spoelstra

Grant, does the AEDB list 9.00-16 tyre diameters so we can compute F15 and F15A engine rpm @ 25 mph?

More tire sizes:
9.00-16, between 34.8 and 35.7 inches
8.25-10 27.8
9.00-13 30.7 to 31.5
9.25-16 33.3 to33.4
14.00-20 47.5 to 47.7

All of the above are from the table for "Regular Pneumatic - Cross Country Tread Design". There are separate tables for "Regular Pneumatic - Highway Tread Design" and "Run Flat - Cross Country Tread Design". Technically, a more accurate road speed to engine speed relationship would be obtained by using "loaded radius" rather than the quoted "free diameter" however the difference between the values will vary with vehicle weight/load, inflation pressure, tire wear etc.

[Hanno Spoelstra]

Thanks Grant for the tyre dimensions.

Tony, I did not realise the power curve of the Ford V8 was that steep!

[Tony Smith]

Originally Posted by Hanno Spoelstra

Tony, I did not realise the power curve of the Ford V8 was that steep!

I would like to see an official GM chart of the 216 power and torque curve should any Chev enthusiasts have one available to compare?

All the online sources I can find mainly deal with the later 216/235/261 on post-war fuel and compression ratios, and how to "Hot-rod" them.

[Phil Waterman]

Hi Tony

I've searched in the past and this is what I found.

http://canadianmilitarypattern.com/2...ifications.htm

Basically as the engine developed they revved higher and produced their power at higher RPM. One of the reasons the 261 is such a nice replacement for the 216.

Will try and find the original source and save the data to post directly.

Cheers Phil