Hey all. I have a 91 RS. I just put in a 350 with 360 HP and about 380 Ft Lbs of torque. My tranny was just rebuilt (700R4) about 5 months ago with corvette internals (better clutch packs, servo, some other stuff, and shift kit). I was just wondering if the power loss would still be roughly 14% or so through the drivetrain even with the rebuilt tranny.

Thanks for the info! If i am pushin about 310-320 HP Id be very happy, but wouldn't it be great if it actually pushed 360!!

thanks

 

For an auto trans, take your HP number and multiply by 0.75 and you will have an approx. number that with be at the rear wheels.

 

you mean to tell me that its losing roughly 90 horsepower through the tranny? I have a hard time believing that not only on a stock tranny, but especially on a rebuilt tranny. Cause if I go by that formula, that would mean that the RS power of 170 HP at the engine would only be putting roughly 127 to the ground? sorry if that were the case my car would NOT move anywhere.

cheers and thanks for the info, but I think I'll look around more.

 

It is flywheel X .80 or .85 = at wheels.

 

thats amazing. How is it so much? though the .85 number looks better to me then .75. A manual car can't be THAT much better. would gears help?

So what kind of 1/4 time could that be if I were to take it to the track someday after a bit more work?

Mind you this thing has dual exhaust, headers, 700 CFM carb.

 

Most chasis dynos show autos loose about 25%...

But hey, if it's numbers you're concerned with, pretend you only loose 2%

 

lol no I do'nt wanna be foolin myself. I just want a respectable (at LEAST 300-305 HP) to the wheels.

 

Go get it measured on a chassis dyno.

How do you know with any certainty that your motor makes 360 HP at the crank? If that's a Desktop Dyno guess, then it's just that, a guess. There's not alot of sense in arguing about the difference between idealized crank HP as predicted by such things and HP at the wheels in reality after the engine is installed in a chassis if you haven't actually measured crank HP on an engine dyno; drivetrain loss is just one of a long list of factors affecting that difference.

Just FYI, stacking up the clutch packs tighter in the trans actually increases its losses; when those clutches aren't engaged, they have to slip, and tightening them up reduces the clearance between the steels and frictions, which makes them rub each other more, which increases overall losses in the trans.

Quit spanking the monkey over things you haven't measured, bypass quibbling over well-established numbers and facts established repeatedly by people who aren't trying to fool themselves, and move directly to reality.

 

Why be concerned about RWHP when you dont even know what you are making at the flywheel?? Yea, 360 HP from the engine Mfg.

Your Drivetrain loss is:
700r4 Auto =20/25%
T-5 Manual =15/18%

But like stated before use any number that will make you feel good with.

And yes your 170 HP motor did have that RWHP, why did you think it was so slow.

 

ouch. Thats pretty pathetic. So your saying that in theory, that a car with 1000 horsepopwer at the flywheel, that is running an automatic, is losing roughly 250 horsepower? I don't know, it can't be that linear. That just seems very odd to me that it can absorb that much.

what about a front wheel drive car? Take my friends eclipse GST, makes probably close to stock powre at the fly wheel which is 210. So hes pushing in reality closer to like 190? (front wheel drive manual, I only took off 10%) Thats so wierd. I know you lose something but it is amazing to me that the numbers are that high!

Why just use a number that makes you feel good? then its not factual and that doesn't matter. In the whole grand scheme of things of the car, does this really matter how much is lost?

thanks!

 

Front Wheel Drive is different...actually more efficient than rearwheel drive...that's why the majority of cars nowaday, are FWD...get's a few more MPG's.

Unsure of the loss, may want to check an import board...

As far as the loss being linear or not...for years I always thought that drivetrains used X-amount of HP, until I began to see posted engine dyno/chassis dyno numbers.

Funny though, I never looked at Tq loss...I wonder if tq loss is the same percentage as HP loss?

 

have to remember that the 170 hp rating is "net in the car"
or "as installed" measured at 77*F and 29.29 " barametric pressure. Much more like rear wheel horsepower.

Your 360 hp motor is rated on a dyno under optimin conditions.
60*F dry air @29.92" barametric pressure. With no accessories,
no mufflers and open tuned headers. Using maximum allowable timing. It is also corrected to
a SAE standard for sea level Pressure and temp.
Your "in the car power" or net rearwheel power" will in fact be about 18 to 22% of that gross rating.
The accessories suck a lot of power especially at high rpm.
so does the trans and rear end. The air entering the carb or
throttle body is warmer and less dense than the conditions
on the dyno.
Your exhaust will be less than optimum as compared to the dyno.
Another drain on power.

With proper gearing that allows the engine to use all its powerband down the quarter mile and decent of the line traction,
you can expect mid to low 13's @102/104 mph from a 360 BHP motor in a typical 3500LB car. If your exhaust system is very restrictive and traction is questionable then I'd expect less out of it.

You'll never know for sure till ya get it to the track.

 

d

 

Factory HP "ratings" are at the crank, not the wheels. A 170 HP "rated" RS puts about 135-140 to the wheels in the real world.

Those "ratings" are with the engine installed in the car, all accessories (emissions things and non-optional stuff like PS, not power seats and A/C and such) installed and operating normally, fuel & timing curves per stock (emissions compliant) specs, the car's production exhaust system hooked up, stock air cleaner installed with the factory filter element, etc.

That's a whole different ball game from an engine dyno.... typically those have a near ideal exhaust, no emissions gear whatsoever, cold air from the dyno cell rather than hot under-hood air, no water pump or alternator or power steering, timing & fule tweaked for max power, etc. etc.

Stop spanking the monkey about what you think, what you imagine, what you "wish" for, what "seems" this way or that, etc. etc. Go get it measured. Test equipment doesn't lie.

Instinct tells me that you probably will turn out to have less than you think. That's usually the way it goes. People's estimates are always optimistic, sometimes comically so.

Let us know what it is when you find out the truth. No excuses, just numbers please; along with a list of what's in the motor and drivetrain.