Torque

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I have been looking, but can’t seem to find any engine torque values for any of our engines. Is it like Rolls that describe their Horsepower as “adequate””.

I am puzzled and would like to know how much torque you get out of a 4 1/2″” piston with a 5″” stroke at 5-6 CR. Any clues?”

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Bill, did you mean a 3 1/2″ piston with 5″” stroke a la 385? Several years ago the Arrow I think published a very poor reproduction of a torque and hp vs rpm curve for a Pierce 8 but I haven’t seen it in a long time. The torque at maximum power can be calculated by the formula torque (in ft-lbs) = HP x 33000 / (RPM x 2 x 3.1416).

The 34/35 Pierce was rated at 140 hp at 3400 rpm which results in 216 ft lbs. Maximum torque occurs below maximum power. Without the benefit of specific dynamometer data I estimate the 385 at 5.5 CR would have peaked out somewhere around 265 ft-lbs of torque in the vicinity of 1600 rpm. I estimate increasing CR 1 point to 6.5 from 5.5 would add about 6% more torque.

Jim

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Cylinder Head 65-70 ft lb

Connecting Road 45-50 ft lb

Main Bearing 65-70 ft lb

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James,

Yes, I meant 3 1/2″. Sounds like it is pretty close to your E-type’s torque. Thanks for the engineering input.

Paul,

Thank you for the values, I was going to be looking for those soon. No wimpy bolts here.

I just got the Morgan engine running, now I will see if I can get the Pierce going.

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Looks as if I need a spelling lesson. Should read “Connecting Rod””.”

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Engine torque is a function of bore and other mechanical attributes, and of firing pressure. As already pointed out by James it can be calculated from the rated HP and RPM, but that is not necessarily the peak torque.

HP = (torque (ft-lbs) X RPM)/5252

I think James’s estimate is reasonable; engine on a dyno tells the tale. perhaps some original test data could be found in an old SAE or ASME technical paper. Engineers frequently wrote papers on new engine designs, back in the day, and included all these sweet details.

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