OK so my car is rated 365 hp at the fly. however, I dyno at 296.5 rwhp. So basically, im seeing a ton of frictional drivetrain loss here. will buying an aluminum driveshaft reduce friction or will it just make my car lighter? is there anything I can do to get a little more of that HP from the fly to the wheels?

 

19% Drivetrain loss, normal... if a little on the high side.

The conditions at the time you got it dyno'd were probably less favorable. I'm not sure if an aluminium driveshaft will help at all... it will reduce rotating mass at the least.

HorsepowerTV or some such show switched out the engine oil, transmission fluid, and the oil in the rear diff with royal purple (I forget exactly what car they did it on, probably on their site) and picked up 15 RWHP... probably on royal purple's site too, they didn't make any other changes, saw the show and found it to be pretty strange.

 

this is all dependant on AUTO or MANUAL? if its manual, somethings a little off there.

 

Most of the 99-02 S281's make around 320 rwhp on the dyno, using the series 2 blower. The numbers on your car are a little low overall. It's not so much that your drivetrain is sucking the power out of your raw SAE net hp #. It's probably either out of tune, or there is a problem somewhere. How much boost is your boost gage reading at 4500 rpm? You should be getting at least 6 psi on the gage. My guess is that it needs re-tuning. First things first, are you seeing the correct boost level?

 

Have you car checked over, even with an automatic it shouldn't be that low. Tire pressure can make 2-3% difference. Inflate them more for the dyno runs and see if that helps.

Over the past several years, I have developed the following "rules" which pretty much explain things I see on dynos.

1) GM rear wheel drivetrains with the M-6: 11.7% losses flywheel rating to RWHP
with the A-4: 14.5% losses flywheel rating to RWHP
Ford rear wheel drivetrains with the M-5: 12.5% losses flywheel rating to RWHP
with the automatic, 15% losses
Chrysler - have seen only one rear wheel drive: 425 HP C300 SRT gave 375 RWHP.

2) Not that some cars are underated. Our 98 Camaro Z28 (305 Hp factory rating) did 297 RWHP new and stock (2000 mi) and that is typical for them. I hear the Ford GT is grossly underrated - produces about what its rating is at the RWs. Some Japanese cars (Mazdas, are over rated slight, and suffer 15-18% "losses" to the wheels with a manual.

3) Crate engines generally produce their claimed rating only an ENGINE dyno (e.g., GM's ZZ383/425 produces right at 425 on an engine dyno). In the car, crate engines produce RWHP equivalent to a factory rating of twenty less than their crate engine HP rating: in a corvette, the 425 HP ZZ383 produces 355 RWHP, just what a 405 factory HP '02 ZO6 produces.

 

i think they did it on the blonde headed dude's 94? gt. on that note, i recently changed my oil from petroleum to castrol syntec, and i noticed a difference right off the bat. i'm bout to drain the rear end and put some royal purple in, don't know what brand is in there when i get a chance.

 

Hey, metaldrummer, I noticed that the 365 HP you quoted is for a SC 281. Is this a tuner (Roush, Saleen)? Some tuners give rather optimistic HP ratings for their cars: they aren't lying but they quote the HP for their model under perfect consitions and based on their prototype (the first one they built) which they put a lot of effort into tuning. After that, they generally just write the prototype's program into each of their "production" cars rather than spend time tuning each:they're trying to make a buck like the rest of us and the two-four hours or so it would take to fine-tune each is money out of their pocket. As a result, I think many tuner cars are down about 3-5% from their claimed rating.

But cars, and conditions vary. This is why it pays to have even a new, stock car tuned - my last three stock cars (two GM, one Porsche) I picked up an average of 8 HP just by taking it to someone with a dyno and engine control module programmer and having them optimize the A/F and other tuning. I think you ought to consider doing this.

 

or the LS GUN camaro

 

ok, the conditions on the dyno day: less than favorable. Ill switch oil and fluids to royal purple. the car makes around 6 psi. im pullying this week to 8 psi and getting a tune. any idea what rwhp numbers id see with 8 psi and a tune? a flipchip is one of those chips with diferent tunes programmed into it right? so you can flip a switch and be on a daily driving gas conservation tune and then flip it again and be on a more agressive tune and so on and so forth correct? are there any pros/cons to these style chips?

 

I've always used a 20% 'factor' with an automatic, any of them.
I've also seen in print from MOPAR (what i used to race for 22+ years) enginnering that you lose 2% per U-joint no matter how perfect you have them.
No one has ever told me how much is lost in the rearend, but it's a lot.
Don't really seem to matter if you have a locker, Trac-loc, or even a full spool.
Aluminim d-shaft won't hurt as well as even gun drilled axles because any weight off the whole rotating assembly, even a couple grams off the pistons will show up and show pretty quickly too.
That is why racers for ever have always been looking at lighter rods, pistons, cranks and all.......