Thread: H/P loss

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I need to know how to figure the horsepower loss in a drive train. I have a 383 strocker in a TA but only get 218 rhp. The car runs pretty strong and was disapointed at the numbers. No E/T runs yet.

I don't think there is a formula for an exact number. If I'm wrong somebody will correct me. But, there are so many variables. What kind of trans do you have? Fluid weight and wear of internal parts will make a difference. Same is true for the rear end, u joints, wheel bearings and every moving part in the drive train.
I think a ballpark figure might be 20 to 25% loss?

Welcome to CHR by the way bul.

for the average rwd car a 10 percent or less loss of power between the crankshaft and wheels is excellent.....
IE u have a 500bhp@crank mtr x .10=450whp@ the wheels....
, problem with that is that a stock t350 GM trans in good condition w/stock or loc up converter takes 23hp to operate, a typical driveshaft in a camro/firebird another 3-5hp, an 8.5 posi rear, which is what Z28/Trans Ams come with is an 11-15hp loss depending on gearin, then u have loss for the weight of the axles and driven wheels to account for, thus, tho .10 percent is great, a 15-20 percent loss is the realistic average...

yep i'd go for the 20% to 25% i had a motor put on an engine dyno made 430hp when i put it on a chassis dyno it dropped by 20% had a shift kitted th350 2500 stall converter 8 inch diff,more weight in the running gear the less you will get to the rear...

I've also heard the 15-20% numbers. The thing to remember is that not all dyno operators know what they're doing. You might want to check out another dyno location if you really feel the numbers are way off.

I'm a big believer in computer dyno sims, and if entered accurately enter, the information (horsepower and torque levels) can be spot on. I have found this to be the case with my Suzuki race engines (within +- 3 HP).

i've heard 20-25. i bet i'm up by 25% with a 727, 3500stall and a ford 9 inch with drum brakes

i dont know alot but im sure an exact way to measure it would be a engine dyno then a rear wheel dyno. if you got the time and money

If you divide rwhp by .75 you'll be close. This only puts you at 291 hp. You didn't post mods or the dyno sheet so I'd have to guess it's either a very mild engine or the dyno was off.

I would have to agree that it is somewhere in the neighborhood of 15 to 20 percent. Post up what you have done to the engine and your transmission, torque converter, type of rear end and gears.

I like the Dyno dimulators also but you have to put in EXACT info or its just junk in and junk out. The only other thing is that you cant really test for is variables like good ring seal, low tension rings, dry sump systems, vacuum compressors, or electric water pumps which can all add pretty significant numbers to the engine HP figures. But aside from that I have found them to be accurate to 5% in either direction which is still pretty damned good for what it is.

- Cudaman -

From what I have heard from some folks that use dyno's quit a bit is 15 to 20 for a standard tranny and 20 to 25% for an auto.
High stall converters will give you some really bad dyno numbers. Most folks I know that have the lock-up torque converters always lock them up on the dyno and get much better numbers. And don't dyno in overdrive. The guys with overdrive put their cars in 3rd gear and have a switch to lock up the converter. I put out some bad numbers on the dyno with a 4500 stall, in fact I put out so bad of numbers I am upset.

Happy holidays to all on here!

There are some interesting calculations that you could use from this site:

Wallace Racing - Automotive Calculators

Why bother? You don't need to quantify something when you already have imperical numbers (like an ET slip). You take what you got to work with and start to refine it. Do you need to know what the dyno numbers offer? nope! you just need understand what you are working with. And start to improve from there. For example, a buddy owns like an 'H' stock camaro - a bone stock 305" motor, quadrajet, HEI, stock cam, stock intake - it is bone stock! and runs in the 10's.

no arguing here

I think you're light with the 20%-25% numbers. I thought I remembered an ariticle that dealt with "...the brutal truth..." of drivetrain losses, and I think it was this one in Car Craft Drivetrain Power Loss - Car Craft Magazine which points to a 35% to 40% loss from an engine dyno to chassis dyno. Like others have said, too many variables for any accurate estimates.