So my car gets 334 whp. Here's some math, with maybe some guessing (guesses have a ~ before them).

Stock whp: ~205
Stock w/ TBB + JR Filter whp: 212.5

Stock hp: ~240

Drivetrain losses: 14.58%

Meaning that supposedly, I get ~248.8 hp at the crank (using drivetrainlosses %).

My turbo, whp: 334

Here's my question - Using that math, can I honestly say that I'm generating ~391.0 hp at the crank? Are drivetrain losses relatively the same PERCENTAGE wise? It's kind of fun to think of my car as a 400 horsepower beast.

 

A percentige loss is just an easy way to describe the frictional losses that increase exponentially as the tranny spins faster. Since you will be increasing the power input and not the speed at which the tranny spins, the losses will be the same for you as for the rest of us.

In other words...the loss for an S2000 tranny is about 15% of 240hp or about 36hp. This is 36hp independant of the actual amount of hp. So, if you are making 334rwhp, than you are making about 370hp at the crank.

That is if I remember my mechanics classes. Please correct me if I'm wrong.

 

[QUOTE]Originally posted by johnyboy32
[B]A percentige loss is just an easy way to describe the frictional losses that increase exponentially as the tranny spins faster.

 

Add...subtract...it's all the same between friends, right?

I fixed it.

 

[QUOTE]Originally posted by johnyboy32
[B]Add...subtract...it's all the same between friends, right?

 

I think your math is a little off.. if I'm making 334 at the wheels with 15% loss, I'm making 393 hp at the crank:

Stock:
204 / 240 = .85, or 15% loss

Turbo:
334 / x = .85
334 = .85x
334 / .85 = x
x = 392.9

And just to double check, 15% of 392.9 = 58.9, 392.9 - 58.9 = 334.

So I make just shy of 400.

 

Hmmm - it sounds like JRM's saying (and I suppose it makes sense), that for a particular drivetrain, there'll be a certain fixed loss at each rpm. So if you do nothing but add horsepower to the engine, that fixed loss will stay the same. Thus, although that fixed loss was, say, 15% of the stock horsepower figure, it's only 10% of the modded hp.

JRM, am I interpreting you correctly?

I admit I'd never thought of it that way, but in retrospect I think it makes sense (to a first order) that this would be the case.

 

No matter what it adds to, thats a lot of horses.

 

[QUOTE]Originally posted by twohoos
[B]Hmmm - it sounds like JRM's saying (and I suppose it makes sense), that for a particular drivetrain, there'll be a certain fixed loss at each rpm.

 

Although... things like viscosity are rarely fixed. For instance, if his turbo engine can spin up the tranny faster it may face more (or less) resistance because various fluid viscosities (tranny & engine oil) change when run at faster shear rates (thixotropic behavior).

But I agree with the thought a constant loss is a good first order estimate.