richard glickel.

I have heard that the difference between horsepower measured at the engine (viz., flywheel?) and the HP @ the rear wheels is something like 15% to 19% less (at the rear wheels).

Would it be fair to estimate that an engine that dynos at 208/209 HP (rear wheels) is at 250+HP measured @ the engine? This estimate is based upon a 17.5% loss from engine to rear wheels.

Any thoughts? Thanks.

ninefiveone

Automatics tend to have greater power losses due to torque convertors and the like (15-20%)

Manual transmissions tend to have less power losses (10-15%)

I'd use 12.5% as a nice middle ground for manuals, 17.5% for auto boxes.

Lemming

Richard,

I dynoed my track car (968 engine) at 200-202 rwhp. If the stated crank HP is 236, then 15% seems to be appropriate. Of course different dynos will give you different numbers and the same dyno will give you different numbers under different conditions.

Damian in NJ

Depends on the dyno. On a dynojet 248 I was seeing 205 before any mods, but it read 180-190 on the dynapak . . . and mustang dyno's show low number too.

flash968

lemming is right - it is highly dependent on wheel weight, tire presure, differential temp and strap tension - it can easily vary as much as 20hp from car to car with those variables, so comparing anoyone's runs is indeed pointless

but, yes, 15% is the standard calculation for transaxle cars and in line with rwhp results and measured losses i've seen

richard glickel.

Thanks for the reponses.

Measurements are Dynopak so tire/wheel friction isn't in the equation as the rear wheels are removed and the hubs bolted to the dyno. Basically, the only "engine" mod is a Michael Mount header. HP was 209 @ 5500 RPM (after which it flattens out).

I guess an 8 - 9 HP gain from the header is about right?

Thanks again.

Damian in NJ

I guess you had your's done in Nyack; when I had my car tested there (twice) the numbers were way lower, showed torque and hp bumps where they shouldn't be, and the redline was off-I went back and forth with them but I guess it was a software issue.