jhans114

iTrader: (3)

Does anyone know the actuall formula for the difference of HP between the wheels and the crank?? Please no assuming need facts. Thanks. Been looking but no luck.

Sonic

There isn't any. Every vehicle has a different drivetrain loss, but as a rule 15 percent loss for manuals, 22 percent for automatics.

2002 SE TX

Someone should get a good dyno of the 2K2, apply the formula, and see if it's really 255 horsepower. Just in case we're getting ripped off, like Miata and Mustang Cobra owners last year

2k2se6spd

So, uhmmmm, whatchya doing next week?

Nismo87SE

That isn't the correct way. The reason SVT recalled the 99-00 cobra's was because owners were dynoing the same power as the 96-98s were. Besides crank power numbers are meaninless anyway. If the 2k2 6spd dynos around 210-230fwhp then it is indeed making the 255bhp.

SteVTEC

There is no hard formula because every car dynos a little bit differently, but you can generalize based on the transmission type.

Cars with auto tranny's lose about 22-28% through the drivetrain, and cars with manual transmissions lose about 15% through the drivetrain.

So for Auto: WHP = Crank HP x (0.75-0.80) (I usually go with 0.775)
For Manual: WHP = Crank HP x (0.85)

Gen5 Manuals dyno at around 190 fwhp, so that's about 15% loss right on the nose.

Gen5 Autos dyno stock between 160-170 fwhp, so that turns out to be about 25-28% loss.

For comparison, the Accord V6 will dyno stock at around 155 fwhp (200HP at the crank, auto tranny only) for a loss of about 22.5%, and the Acura TL-S/CL-S (also auto tranny only, 260HP) dynos right around 200 fwhp which also about a 22.5% loss.

So no two cars are identical as far as drivetrain losses, but the best you can do is generalize and go with the average losses (25% auto, or 15% manual) if you don't already know where a car typically dyno's at.

Deac

I never did understand this whole "at the wheels and at the crank hp" thing...justtell me the overall HP is what I always thought...Thanx for the info. So...if I understand correctly, does at the crank = overall HP and at the wheels we should apply that formula? Whats the differnece between overall HP, at the wheels and at the crank? Do they all have separate formulas? Holla back....

Deac

SteVTEC

Deac,

All engines put out a specific amount of power "at the crank" - meaning, right at the crankshaft of the engine. This is how engines are rated. For example, 200HP in my Accord V6, or 222HP in a Maxima (255HP in the new ones!!). This is all crank horsepower.

However, not all of this gets to the wheels...

An engine is connected to a transmission, and the transmission requires energy to spin (losses), and the transmission of power is not 100% efficient either (more losses). The transmission then connects to a differential, or final drive, and then to some shafts, and then to the wheels, and finally to the tires which actually touch the road. All of these components require energy to spin, and don't transmit power 100% efficiently.

The net result? Not all of the power that then engine makes at the crank makes it to the wheels. So hence the differences between crank power, and power at the wheels.

stjohnr

The Theoretical Indicated Horsepower
delivered at the cylinder is as follows

IHP = ( Mip * L * A * N) / 33000

whre Mip = Mean indicated pressure
L = Stroke
A = Area of Piston
N = number of power of power strokes per minute.

Deac

Thanx for the explanation!!! I never knew what all of that stuff meant...I've yet to be Dynoed too so now when I go, I'll know wha the hell all this stuff means! Thanx again!