TVROguy

Guys, what is the formula for the relationship between Engine
HP = ___ BHP = ____ RWHP?

baxsom

it depends on the transmission. autos supposedly lose more through the transmission than sticks.

nj02vette

The old rule of thumb was 88% for manual, and 82% for Auto. But that's just a guestimate and doesn't scale with higher hp cars.

So if you have a manual with 350hp, it should have about ~310rwhp.
Auto would be less at ~290rwhp.

TVROguy

It's a 6 speed 99 Coupe ... dyno-tuned at 420 RWHP ... so, the engine is producing about 500 HP?

ZZ06

....mmmm more or less. i always went by the old 10-15% drivetrain loss, which can equal 50-65hp loss from the flywheel

Joe_Planet

hp=bhp

the b stands for brake

AU N EGL

what was done to the engine? if its an LS1 engine, not likely to be that high

ZZ06

very true. that would have to be full boltons and a pretty decent sized cam WITH a tune.....

TriplBlk

Hope you don't mind..mods in his profile....


"Patriot heads & cam, LS6 Intake & injectors, ported LS6 oil pump, 160 degree thermostat, LS7 clutch & flywheel, Blackwing filter, ported/descreened air flow sensor, Cold Air Screens, Corsa Touring Exhast, Drilled & Slotted Bendix rotors, Black calipers, BPP short shifter, Ipod2Car interface."

Dope

475-500hp is a pretty safe range to quote, I'd say.

Dope

AU N EGL

Which heads and cam ?
Have a dyno chart

David426

12% loss for mn6 and 18% for automatic.. Thats for our C5 Corvettes... There is also parasitic loss for independent suspension vs solid rear.. F-Body Trans Am and z28 with LS1 have solid rear so these numbers do not apply .. Also drive train loss on rear wheel vs front wheel drive cars..Irrelevant,, just an FYI.. so the mathematical formula is this
350(BHP for stock LS1) x ( 0.82 for manual tranny) or 0.88 for auto trans
so 350 x 0.82 = 287rwhp for an auto
and350 x 0.88 = 308rwhp for a manual
478 x 0.88 = 420rwhp for your car so 478 brake horsepower is what you have.. This is not an exact science but pretty dang close

zeevette

Stock '02 ZO6 is factory rated @ 405 HP, and most dyno about 345-360 RWHP corrected SAE, which is about a %13 drop. After I finished with my NA build, it did 483 RWHP corrected, and then the clutch gave up. I got some custom badges from this guy in Poland; set of 3 for $25 included shipping! They were ordered by some guy who never bought them, and they said 525HP. I figured this was pretty conservative, and I couldn't pass up the price. However, the quality wasn't up to the standards of that Justin guy that does them in the USA, for a lot more money. Now, of course, they're not even close, and they're coming off when I finally remove my BSMs.

ZZ06

wait what? Im confused. I was just commenting off of yours from earlier and agreeing with you in saying if it was an LS1 it wouldnt be that high at all. Infact thinking about it and knowing some of my old buddies cars....that would have to be one hell of a monster cam to make 420rwhp w/o heads.... or one happy dyno.

AU N EGL

Yup

dougbfresh

Why does it matter, it's what the wheels get that matters.

chaase

That is not a particularly big cam. I put down 419rwhp in my auto and the lope is barely noticeable.

Chevy Guy

Rear wheel horsepower is at best a ballpark number and is only relative to the dyno being used. Hot Rod did a write up not so long ago and compared several RW dyno's on the same car they got wildly different values varying as much as +/- 100 hp.

Basicly the way to go is engine HP minus 12-15% = RWHP.

sunchaser73

Here's my $0.02 on the subject: my engine made 602 hp on an engine dyno, and then made 519 rwhp on a chassis dyno. So, 519/602= 86%, or a 14% loss through my drivetrain. I have always used the thumb rule of a 15% loss through a manual transmission, and my dyno numbers seem to support it...

David426

Yes, I have done a Thread on this subject.. People just refuse to believe this or just ignore it and think that a dyno is a dyno, or its like getting on a scale and weighing yourself.. NOT! The Dyno is just a Ballpark figure at best.. Way too many variables..