professorX

Hey everone I was just woundering if a person wanted around 450 hp to the rear wheels in a 85 vette how much would have would the engine have to be produceing at the crank and what is the normal powertrian lose for c-4's .

Paul Workman

Good question and interesting topic! And, measured results depend on the type of dyno used, e.g., inertial (drum type e.g. Dynojet) or a static (crankshaft) engine dyno. For practical reasons, the dynamic dyno is what gets quoted the most. (It may more accruately predict drag strip performance - results include accelleration of rotating mass and is measured at the wheels - and the engine doesn't have to be pulled to make the measurement)

For instance, an often used factor for manual transmissions on dynamic dynos is 0.85. Dividing rwhp by .85 ≈ clutch hp...maybe. So, for 450 at the wheels, the clutch hp is going to be roughly 450/.85 = 530ish ±

HOWEVER...This formula assumes the loss is constant regarless of clutch hp, and assumes a fixed inertia factor regardless of actual transmission used or other components. So, in reality a fixed "0.85" is probably a tad(?) ambiguous - if not plainly simplistic. For example, rwhp on a 500 hp LT5 will vary by approx 15 hp when switching from the stock dual mass FW to an aluminum Fidanza. The type of flywheel (one example) has an effect on that 0.85 factor.

One other very important consideration is "power under the curve". In other words, peak values seldom tell the real story. Oh, peak numbers sells a lot of cars or camshafts, but when it comes to quarter mile times, the highest average torque at the rear wheels over the entire course is going to result in the fastest speeds and shortest times at the track.

Like I said...This is always an interesting topic (to me).

P.

professorX

Thanks for the input, glad to see someone was thinking the same thing.