mutzman951

Fellow addicts,
What is the conversion factor for determining power loss thru the drivetrain. My P/O had the car dyno'd B4 I bought it and it put down 242 rwhp. What is the # to convert rwhp to fwhp. I've made considerable mods. and want to know how much hp I've added to it. I'll be getting it dyno'd in a few months, or so.

On another topic, I raced a guy in a WRX Suby the other nite, killed him on the straight, but he could have rammed me on the on ramp. I lost his lights under my spoiler....he could have pushed me! In the excuses column, my front tires are beat, and the adjustable spring perches are uneven, but he spanked me on the curve. (Maitland Blvd W. to I-4W).

We blasted onto the Highway, I wound out 3rd (103mph), then i waited for him to catch up,...
..I say "man, that thing handles great!"
He says "Thanks, I built it myself! That thing's fast as sh*t!"
I say..."Thanks, I built it myself!"
We honk and wave, then drive off....both smiling!

I got susp. stuff for xmas, and I'll get to putting it on this coming week. the old front tires are soon to be gone, too.

i guess my work will never be done, thank God!

doug

New, and to be installed: KLA Industries strut brace, Cup Car adjustable rear sway bar with aluminum carriers and delrin bushings, and new tie rod assy's. Santa has good connections!

turbo944

Hehe...sounds like fun! Now get that suspension stuff installed so you can lose him in the turns.

The accepted number is about a 15% loss through the drivetrain. So add 15hp to your RWHP number per 100RWHP. So 300RWHP would be 345 hp at the flywheel. Of course that's if the figure is based on the RWHP and added to it. If you went from the FWHP and subtract 15%, 345FWHP would be 293RWHP. It's pretty close either way....

Nope....the work is never done....lol...but that's okay, otherwise you wouldn't have anything to do when you weren't driving or washing it!

adrial

Better way of doing it:

Accepted is 12-15% drivetrain loss IMO on a dynojet or similar.
So if you use 15%...

RWHP/(1-.15)=FWHP
FWHP*(1-.15)=RWHP

turbo944

Okay, somebody just had to show the math

I like the SWAG method....Scientific Wild A$$ Guess. Same way artillery used to be fired when they knew where you were according my marksmanship instructor who was in the arti back in Vietnam.

mutzman951

I don't get it, sorry,

285 - 15% = 242.25

242 + 15% = 278

I guess my real question should have been "by what factor do you multiply the dyno hp result to ascertain the fwhp?"

With all the stuff I put on my car, I guess the only thing that matters is who sees who in the mirror. Since I've done so much work to my car, I get lots of questions from people about hp. I just wanted to have an exact answer.

To quote my 911 RS friend..."More than 300 hp from a 4 cylinder engine is unnatural!"

Doug

adrial

mutzman, just reread what I said...

The bottom line is that the number that matters is RWHP not FWHP.

fortysixandtwo

I always did it this way.

FWHP *.85 = RWHP
RWHP *(1/.85)=FWHP

As adrial said it's the RWHP that matters.

turbite

doesnt FWHP usually stand for "front wheel horse power"
not "fly wheel horse power?"

DanD

Here is MY formula. (ok someone else's ...)

RWHP/.85=Crank HP
(I won't feed the FWhp flames..)

Danno

An even easier method:

rwhp / 0.85 = bhp
bhp * 0.85 = rwhp

Some previous discussion on transmission losses: transmission losses on dyno run

Also PDF version of original thread:
011230-TransLossesOnDyno.pdf

josephsc

Wow - that's much easier. I've been doing:
LOG( bhp ) - 0.15 = LOG ( rwhp )
LOG( rwhp ) + 0.15 = LOG ( bhp )

Silverbullet951

Danno

Anyone know what the drivetrain losses on a front-wheel drive car is? Figured with the drive-shaft and those bearings removed, along with no right-angle R&P to deal with, you can cut those losses quite a bit.