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.
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.
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
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?
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.