/.82 = whp to chp conversion.

[MadMike]

so i figured out what the math is finally,
just take the whp and /.82 and boom! acurate to 3%

like with my car, 247whp /.82 is 301chp

neat stuff i think :D

[olblueeyesbonne]

I dynoed the SSEi in @ 254.xx whp and was told 317-322 CHP, but with the /.82 it is 310.xx CHP, FWIW.
My track times with the weight and gearing show around 320, so that may be off slightly, but it all depends on how much play you have in your stall/trans etc..

[willwren]

That's not solid math, but a vague guideline. Your drivetrain loss will vary with the build/wear/age of your trans and your torque converter.

[MadMike]

like i said, its acurate to about 3% maybe a bit more,
but thats the rough way to figure out what you got,
and reverse math if you know your chp and wanna get your whp.

i was drunk when i posted this thread last night gimmie a break lmao

[00Beast]

Yeah, 20% is a good rough estimate of drivetrain losses. It's a little more on FWD cars and a little less on RWD, but 20% is a good average.

[CMNTMXR57]

I've always gone by 15%, but that is on my RWD vehicles.

GM "Rated" my LS1 in my Camaro at 305. But in reality, most LS1's were doing 340 - 350. This would fall in line with my stock 292rwhp that I pulled on a DynoJet 248c. Backed up with several 289, 290, 291, etc. That divided by .85 would be 340, 341, 342, & 344 crank HP (rounded).

Then my GTO, where GM fessed up and made it an honest "rated" amount of 350hp, I did 297rwhp stock. This despite figuring my IRS in that car should soak up more power than my solid rear 10 bolt like in my Camaro. Figuring it still at 15% would put it at 349 crank HP which is more realistic. If I did 20% factor, it would come up at 371 crank hp, and I know that's not realistic.

[MadMike]

yea with rwd theres less loss it seems,
ive been lookin all this stuff up lately,
unusually while im drunk more than anything haha

[John Deere Boy]

Is crank HP the same as brake HP, or is one or the other measured without engine accessories?

[willwren]

Hate to tell you, but 20% is on a good solid rebuild for a FWD. Most cars here are probably pushing closer to 25% loss, with some over 30. That formula can't be within 3% just when you factor RWD vs FWD alone, not even taking into account the greater than 5% variability of FWD drivetrains.

If you want to narrow in on it, run the calculators based on your 1/4 mile time and use them to compare to your math here. To be honest with you though, this formula isn't likely to be any better than 5% or worse error if it's taken from a sample size of 10 or more cars on this Forum alone.

[gonzo4191]

[willwren]

Elaborate a little?

[CMNTMXR57]

Hate to tell you, but 20% is on a good solid rebuild for a FWD. Most cars here are probably pushing closer to 25% loss, with some over 30. That formula can't be within 3% just when you factor RWD vs FWD alone, not even taking into account the greater than 5% variability of FWD drivetrains.

If you want to narrow in on it, run the calculators based on your 1/4 mile time and use them to compare to your math here. To be honest with you though, this formula isn't likely to be any better than 5% or worse error if it's taken from a sample size of 10 or more cars on this Forum alone.

Stock I was trapping at 103. Which put me right where the Dyno-Jet was indicating. With pretty much all "bolt-on mods", I was 109. After engine work, it was in the 113'ish on average, a few higher otherwise. So I understand what you're saying, but sometimes conditions at the track, driver error, and mechanical failure contributes to the "it isn't always perfect either". Trust me, I've had several spectacular runs, only for a clutch to go south upon banging it into 3rd. Or the sh*tty hydraulics on our system, keeping me from disengaging the previous gear I was in, and not allowing me to shift it to the next cog.

At least with a dyno, you can get an SAE corrected amount, saving wear, tear, and driver stupidity. Not that it's the be all, end all. It, like your MPH, is just another tool in the arsenal.

[willwren]

Exactly. You have to take the formula with a grain of salt, but compare it to other tools to get the clearer picture.

[l67poweredlss]

yea with rwd theres less loss it seems

Actually, FWD is a little less. There is one less thing in a FWD car to rob power that a RWD has, a driveshaft. RWD still has more usable power when launching due to the weight transfer on the drive wheels instead of off the drive wheels. All in all with identical engines in a FWD and RWD car, the RWD car will still run a better time in the quarter due to the launch. However, the FWD car may trap a mph or two faster.

[BonneMe]

yea with rwd theres less loss it seems

Actually, FWD is a little less. There is one less thing in a FWD car to rob power that a RWD has, a driveshaft. RWD still has more usable power when launching due to the weight transfer on the drive wheels instead of off the drive wheels. All in all with identical engines in a FWD and RWD car, the RWD car will still run a better time in the quarter due to the launch. However, the FWD car may trap a mph or two faster.

Based on what?!?

[00Beast]

I have never heard of a driveshaft taking more than 1% of power unless it's filled with lead or something. FWD transmissions have a lot more moving parts than a RWD trans.

[willwren]

In general, FWD transmissions are not as efficient as RWD. I'm not sure where LSS got that information.

[l67poweredlss]

I'm not sure where LSS got that information.

A guy who worked at the shop that dynoed the LSS told me this. I asked him why my numbers were high and he gave me that line. It doesn't surprise me that he is wrong. The guy was a complete moron and almost crashed my car driving it up the ramp.

[willwren]

If it helps, I grew up wrenching on cars when imports were RWD. I lived and learned through the FWD transition. As close as you can draw a comparison, a FWD trans in general will never be as efficient in transferring power as a RWD trans.

Some of this has to do with the necessary compact design of the FWD trans to fit it into the engine bay in a transverse fashion, and some of it has to do with thermal efficiency with that much crap packed into the smaller package. Heat is the primary enemy. The viscosity of your fluid is what it's all about. FWD transmissions will generally run hotter.

[l67poweredlss]

Some of this has to do with the necessary compact design of the FWD trans to fit it into the engine bay in a transverse fashion, and some of it has to do with thermal efficiency with that much crap packed into the smaller package. Heat is the primary enemy. The viscosity of your fluid is what it's all about. FWD transmissions will generally run hotter.

Yeah, I never knew just how hot our trannies got until I rented a new Grand Prix once. It was 40* outside and the trans temp was 195* going easy on it. Go WOT just a couple times and it shot up to 210*. The G8 usually sits around 160* when its HOT out. The highest I ever seen it was 182* and I was driving real hard.