Torque through driveline losses

stixx said

Don't know a thing about chassis dynos, but I expected (kind of) that it would give numbers that are in "tune" with the numbers taken on a engine dyno.
While I follow your equation the result doesn't make sense either, since 330ft lbs is mighty low for a 410 stroker.

The numbers given by James and jbc do not correlate at all... horsepower is a mathematical function of torque (as has been said many times), and 525ft lbs
doesn't make ANY sense. When max torque is at, say, 4500rpm, this would [mathematically] equate to 449 RWHP. ??

Click to expand...

Mistakes are being made by not making torque and RPM conversions for the gearing in the drivetrain. And yes, stixx, 330 ft lbs from the engine is indeed too low for the ET's per pure peak HP numbers but I'll explain below.

If you take the OP's 355 RWHP, and use a 18% loss factor, that is 433 HP at the crank. Plug that into the Wallace calculators with 3150 lbs (car + driver), and it spits out the ET of 11.29 and speed of 119 mph. So the wheel HP number looks plausible.

Where the OP's numbers 'go off the rails' is for the torque that the OP reports. Converting from RWHP to WHEEL torque is done at the WHEEL RPM's, not the engine RPM's. If the peak wheel HP is at an engine RPM of say, 5500 RPM then the wheel RPM's are 5500 divided by 3.91 = 1407 RPM. (Assuming the trannie ratio is in 1:1 gear.) Take that to any online HP to torque calculator, and you get 1325 ft-lbs of torque for the whole rear axle, or 662 ft lbs per each wheel. (This is not peak wheel torque but wheel torque at peak wheel HP.)

Since peak torque at the wheel in a fixed gear run-up is at a lower RPM, then the peak wheel torque can be expected to be something like 5-10% higher, and would be around 700 ft-lbs per wheel or 1400 ft lbs for the whole rear axle.

So, the OP's torque number does not look like a wheel torque number..... or is just a flat out mistake.