Thanks.

 

The conversion depends on the vehicle. M6 or A4 ? How much converter?
What gear was it run in (either trans)? Were chassis dyno numbers corrected? To what? Tire size and pressure?

The most accurate conversions would be for an M6 run in 4th with a 3.42 or 3.23 axle and stock tires, because lots of people have run that, and there are some whose engines have also been run on an engine dyno. As far as exhaust you'd need engine dyno figures with the same system installed.

You'll hear claims of numbers around 12-15% for the conditions above. That's probably close, so 300 rwhp would be 340 to 350 fwhp. With a loose converter (not run in lockup) you are probably just "WAG"ing rw to fw conversion. This would be a case where you'd use the chassis dyno to evaluate changes, not get true fwhp numbers.

This isn't carved in stone, and your results may vary.

My $.02

 

edited: get the correct formula from oldsstroker.

stock 6 speed with 10 bolt and stock wheels is about 16%

non lockup automatic with steel driveshaft, 12 bolt, and slicks could be as much as 25%

of course this is an estimate all based on how close you are to your actual drivetrain loss percentage.

your local dyno shop should be able to do a deceleration test and determine your drivetrain loss fairly well.

 

How does one "lock up" the TC on an Auto Trans car when doing a dyno pull?

Steve

 

Well, mathamatically, if you have 18% drivetrain loss from fwhp to rwhp, and you know rwhp, you should divide rwhp by (1-.18 or .82).

So 523 rwhp /.82 = 638 fwhp.

If you measured 617 fwhp and knew you had an 18% driveline loss, that loss would be .18 x 617 or 111 hp. 617-111 = 506.

Don't shortchange yourself. Of course, the 18% is just an educated guess in most cases.

 

thats right i knew i had something backward.. since its a loss you do it the way you say. but as above the best way to determine it is a deceleration test.

 

Hmmm...well a decel test checks a lot of things including aero drag and front wheel drag (on a rear driver), but it really doesn't check power-induced friction loss in the rear end or trans, especially an automatic, nor converter loss. As power goes up, trans and axle losses increase dramatically while transmitting the power. In extreme cases the gears actually push sideways enough to deflect the gearcase or load the bearings so much that they cook.

If there is a 'best way", it's to dyno the engine then install that engine in the vehicle and run the chassis dyno test. I'd guess that's what Cup teams do. I've seen Superflow do that at their factory.

My $.02.