My question is what is actuall difference in power loss between the 2. I know the auto will take away more power than 6spd but what are the actuall numbers and also can I improve my auto (stock with 2800 stall) by getting it modified to lose less power.

 

The numbers I've seen quoted are 12% powertrain loss for 6 speed and 18% for A4. So if you have an A4, multiply 350 by .82 = 287. Hmmm, sounds about right. For a stock C5, the cheapest/easiest way to gain hp is long tube headers and a true cold air intake (one that draws in air from outside the engine compartment) such as a Callaway Honker, vararam, Vortex Rammer etc plus a tune.

 

I'm putting down 417 to the wheels with a HIC combo I was just wondering if I'm losing more power than I was supposed to.

 

There's really nothing you can do, don't worry about how much power your auto is eating up...Just see how it does on the track, that's the true indication of how well your car performs...

 

Actually you can do it two ways:

A4 you can multiply RWHP by 20% then add it to the total RWHP and that will give you your Crank HP

OR

A4 you can Divide RWHP by .82 and the total will give you your Crank HP.

Folowing the same formula above for a M6:

You multiply 15 %

OR

You divide RWHP by .86 and that will give you the total.

Remember that one you divide and the other you multiply and then add it to the total of the RWHP!

Thanks,Matt

 

for Rear Wheel Horse Power KNOWING Engine Horse Power and GUESSING the % loss thru the drive train :

RWHP = Engine HP X (1 - guess % of loss)

AND

for Engine HP KNOWING Rear Wheel HP and GUESSING the % of loss

thru the drive train :

Engine Horse Power = Rear Wheel HP divided by ( 1-guess % of loss)

So, for an M6 using the guess loss (12%) figure from the 2nd post:

RWHP = Engine HP X (1-guess% loss) =Engine HP X (1-.12)
= Engine HP X.88 = .88 Engine HP ;

Engine HP = RWHP divided by (1 - guess % of loss)
= RWHP divided by ( 1-.18 ) = RWHP divided by .88

Again, using the guess loss (18%) figure in the 2nd post for an A4 :

RWHP = Engine HP X ((1-guess % loss) = engine hp X (1-.18)
= Engine HP X .82 = .82 engine hp ;

Engine HP = RWHP divided by (1-guess % loss)
= RWHP divided by (1-.18) = RWHP divided by .82

These are "engraved in stone" mathamatical relationships. The Formuli DO NOT change from one car to the next BUT its the
"GUESS % of loss" that varies from one person to the next.

So, even though the Formuli are correct, different people will make different % of loss guesses and, thereby, will get different HP figures.
In fact, Tony Mamo , and many others,do not believe in the
"fixed ( throughout the entire RPM and rear loading spectrum) % of loss".

Regardless of your school of thought, since we're guessing at the percentage of loss thru the drive train, the BEST these Formuli will give youi is a good(?) aproximation of Horsepower.

 

Since every combo is different the only real way to know your loss would be to.
1. Remove your engine from your car and dyno it.
2. Reinstall your engine and run it on a chassis dyno.
Then compare the difference and you will know your loss on paper.
But then take comfort in knowing you will be faster in 1/4 mile with the auto over a 6 spd in the same car.

 

good info- thanks

 

Well, you do leave some HP on the table with a A4. But, I kind of like the idea of a fixed number of HP is needed to drive the drive line rather than a portion of the total. Still that would not tell you how much you are leaving on the table. I would think its less than the normal ratios that are talked about, but that is my opinion.

I do not think there really is anything to do to a A4 that would reduce the amount of power loss. A higher stall will just help rpm levels on launch, it will do nothing for power loss.

You can reprogram the computer to shift a little better and to adjust the torque reduction done when shifting. However, it won't add to the power when in gear.

If you drag race, the A4 is best. But, if you don't then you could swap to a 6 speed. Its a LOT of work and is most likely not worth the 15 to 30hp that may be gained. But other factors could make it attractive.


What do you do with the Vette? 1/4 mile, street or ? Is there something besides dyno numbers that bother you?

 

Just out of interest, why? (I'm not disagreeing with you in any way...I'm sure you're talking from experience, but why would a manual be slower?)
Cheers

 

Because you're shifting it...

 

You're not dropping in RPM's the way you would do with a manual. A computer will always win the shifting contest over a manual.

But as others have said it really depends how, where and what you want to do with your car that dictates a six speed vs an automatic.

 

Great info guys Thanks a lot. I had stick cars all my life (still do)but the fact is they just suck for me at the track (very hard to be consistent) and I'm not even going to mention all the races I lost becouse of missed gear. So basically I'm just looking to be consistent at the track and ocasionally on the street.

 

The the auto tranny is the ticket for you.

 

Mostly because with a manual you are missing the torque multiplication of the converter.
Most people think it only comes into play on the launch but it isn't so it's also there with every gear change and even more so when using a higher stall/torque ratio converter!
If you ever notice when doing a back to back dyno on just the install of a converter the torque will always come up while the Hp decreases but the car will be quicker.
Usually in the .5 sec. range.