DYNO - rear wheel horsepower conversion

[StephenK]

On a car like mine, 2006 SL600, what percentage would you use to convert rear wheel horsepower. I have been told anywhere from 15% to 25% LOSS.

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[JAYCL600]

Originally Posted by StephenK

On a car like mine, 2006 SL600, what percentage would you use to convert rear wheel horsepower. I have been told anywhere from 15% to 25% LOSS.

thats a big swing, because its such a big swing most people dont use that figure, i mean who cares what the engine makes on its own while not attached to the drivetrain, thats what that figure represents. RWHP and trap speed tell u a whole lot more about the catual real world horsepower the vehicle is making.....now after all of that I use 18% Whats being done to your car now Stephen?

[RBYCC]

Originally Posted by StephenK

On a car like mine, 2006 SL600, what percentage would you use to convert rear wheel horsepower. I have been told anywhere from 15% to 25% LOSS.

Depends on the dyno.

Mustang dyno which is a load type may show drive train loss as much as 30%
Dynojet which is an inertia type will show 10%-15% depending on weight of car.

Just completed a twin turbo install on a 3.0L M103-12V.
Base line pull was 30% from published flywheel numbers.

[StealthAuto]

Typically manual cars lose between 14-17% percent and automatics lose around 20%.

4WD vehicles usually lose around 25%.

I hope that helps.

[steve872]

The accepted power train loss numbers for MB are 18% loss for autos and 15% loss for manuals. Bob Brady from Renntech confirmed this to me as well as just about any major MB tuner out there so you are very safe to use these percentages. 2 years ago Acura was claiming a certyain bhp numbedr for thier car and once tested it was shown to be 15bhp lower so the SAE recalculated the program for determinng BHP and still I know some new cars still have high end BHP claims. Dyno jet tells all. Top Gear road tested the new Mustang Shelby GT500 and it made less than what Ford claimed. The video is on Youtube.

[new guy]

Originally Posted by steve872

The accepted power train loss numbers for MB are 18% loss for autos and 15% loss for manuals. Bob Brady from Renntech confirmed this to me as well as just about any major MB tuner out there so you are very safe to use these percentages. 2 years ago Acura was claiming a certyain bhp numbedr for thier car and once tested it was shown to be 15bhp lower so the SAE recalculated the program for determinng BHP and still I know some new cars still have high end BHP claims. Dyno jet tells all. Top Gear road tested the new Mustang Shelby GT500 and it made less than what Ford claimed. The video is on Youtube.

If you actually watch the video, you'll see that they expected the car to make 500 rwhp, which is NOT what Ford claims. It's Top Gear that came out looking like idiots, not Ford.

[new guy]

In fact, here's the video:

http://www.youtube.com/watch?v=mGbhKQlUhLo

Pay close attention at 3 minutes, 30 seconds. This is when they put it on the dyno. It puts down 447 rwhp, which is approx 525 at the crank with a 15% drivetrain loss. 25 hp MORE than Ford claims.

Top Gear = Idiots.

[jeff.bisonett]

I've had good luck with using 1.21 as a factor for dynojet(~18% loss) and 1.28 as a factor for mustang dynos (~22% loss).

Reference:

http://forums.mbworld.org/forums/sho...0&postcount=16