Am I the Only One Who Thinks This Way?
 

When we talk about RWHP vs. Flywheel HP I see 10 to 20 percent for drive train loss to get to a flywheel number on a 5-spd. Here is why I think that logic is flawed. Lets take my bone stock 93 LX wife driven coupe. 205 factory rated HP (or 225, thats another post). Using 20% loss through the drive train would equal 164 RWHP. Now throw in a 1300 HP Outlaw motor under the hood and use the same 20% conversion. That would equal a 260 hp loss and equal 1040 HP at the wheels. If you took this to its logical extreme that means that the stock motor would not even be able to turn the transmission much less move the car.

I'm not saying there is no drive train loss, I'm just saying the the loss is a fixed number and not dependant upon how much HP your motor makes.

Your comparing totally different transmissions, 1300hp Outlaw motors are mated to special transmissions that use way less horsepower, they are designed for drag racing, and that only.

Take your stock 225hp, then you take the 15% drivetrain loss in a 5-speed:
225x.15=33.75
225-33.75=191.25

So 191.25 hp

I'd say that is DAMN close to what a stock 89 GT puts out.
And we all know even though the 93's were rated lower, they still put out around the same amount of hp.

I don't undestand what your saying? I think even if you car had only 164rwhp, it would still be able to move the car.

hes comparing the trans loss form teh outlaw car to teh total horepower of the regular car

WHich more then the regular car so it coudnt move

Let me try again.

Lets take my stock 93 LX coupe with a T-5 (205 hp) and bolt on a nice new procharger P1SC. I run down to the chasis dyno and turn (305 hp at the wheels). To convert to flywheel HP using the 20% conversion would mean that the same T-5 drivetrain is soaking up 61hp instead of 41hp with the only change being the new blower.

Taking it one step further. Lets say I add heads, Intake, exhaust and a cam. On this visit to the dyno I turn 405 at the wheel while still using the same T-5. Using the same 20% percent conversion means that the same drivetrain is now a 81 hp drain.

It is true that there is a parasitic loss through the drivetrain. I just don't think that it increases with horsepower. I think it stays a constant number as long as the drivetrain is unaltered.

I hope this makes more sense than my original post.

parasitic losses are mainly from the friction of the drivetrain.. also thermal losses..

as speed increases, so does the drag or friction coefficient..
so the percentage of loss remains relatively constant..

so an engine that puts out more hp is spinning faster within the same time frame. The faster engine speed means more drag or friction..

That makes sense.

Has anyone dynoed a motor before installation into your car and then followed up on a chasis dyno?

I had my car dyno'ed and was 262 at the rear wheels. If you add factor in the 15% loss (actually you need to divide by 85%, not add 15%) it comes to 308hp at the flywheel which sounds about right for the kinds of mods I have. (GT40 setup)

Tom