jthurik

I have been thinking about this my car makes 811rwhp thru a stalled auto. Everyone claims this tranny eats 25% of your power and I just do not think that is the case. If so my car would be 900+ wheel with a Manual and I have never seen a built motor D1 car make that kind of power. I did believe the drive-train lose at first but after talking with my tuner and others I think if i put a manual in it would not pick up any power or if it did it would be not more then 10-20hp. I have seen autos and manuals make the same power stock to stock. I have also seen where a A6 was replaced with a M6 and no power was picked up. Let me know your thoughts and why you agree or disagree.

Flash20

I somewhat agree especially if they locked your converter during your dyno pulls.

all of my pulls are with the stall unlocked.

Ragtop 99

I don't think I've seen anyone use a 25% loss factor for the A6.

There have been some pretty good threads about drivetrain loss. The consensus is that using an average percent doesn't do a good job of estimating marginal power loss when you make a major step-up in power such as adding a blower.

At your power level, 20 - 50 HP would be range I'd estimate you are down compared to an M6. A lot depends upon how efficient your converter is.

TMyers

IMO using a percentage is the wrong way to look at it. It takes X amount of torque or HP use what ever term you like to turn something. With the M6 you have fewer components that need to turn so you have less loss.

Ragtop 99

For understanding drivetrain loss, the short answer is at post 5:
http://forums.corvetteforum.com/c6-z...engine-hp.html

More discussion is in this thread:
http://forums.corvetteforum.com/c6-t...heel-loss.html

LS1LT1

I've never seen that high of a number used either.

Another small factor to consider here is that the A6/6L80/6L90 does not have a true 1:1 ratio in it, the cars are dyno'd in either 3rd or 4th gears putting it slightly above or below 1:1 which can skew the numbers at least a little bit.

Gearhead Jim

Post 5 was good.

Since the LS3 numbers are SAE certified, we should be able to check what people with stock LS3 engines are getting at the rear wheels, and work the percentages from there. Keeping in mind the variables in dynos, conditions, etc.

I've heard that for rough numbers; one can use 10% for the manual tranny and 15% for the A6, keeping in mind all the variables that Glass Slipper mentioned. Do the 10%/15% work out about right, or something different?

White_Lightning

i always thought 10-12% for MX.. 14-16% from auto..
not sure on the 15% number

corvette4595

I'll know exactly what the loss is Friday when my stock LS3 A6 gets dynoed. This will be the baseline dyno before the mods begin and I'll use 430 as the bhp number when calculating the loss. The only variable here is that I'm assuming the 430bhp rating is accurate.

jmil1974

No, it does not take a given amount of power to turn something. It is proportional. To further complicate things, it's not linear either. Rule of thumb is 15% for an M6, 18+% for auto (with locked converter). This is for 10 bolt solid rears. IRS adds 1-2% loss. Dana, 9", etc. add a bit more even. Only way to measure for sure would be to put a mill on an engine dyno, run it a few times, then put that same engine on a chassis dyno, under the same conditions, and run it a few times. Even this is problematic given the variances from dyno to dyno. Most efficient is the M6 and small, solid rear axle. Only major ways to improve are a lighter driveshaft, lighter clutch, flywheel, and lighter wheels and tires. Obviously, the inverse (heavier driveline and wheels) increases the loss further. If you want a dyno queen, don't run big rollers...
http://ls1tech.com/forums/gen-5-cama...99-camaro.html
...and yeah, it was inconsiderate of GM not to give this tranny a true 1:1. Glass slipper's explanation is the sh*t!

JoesC5

Re. post #5 you mentioned. Note that he believes that GM's horsepower rating for the LS7 is at the wheels instead of at the flywheel.

He posted....."For Z06s, stock LS7s with 505 HP (SAE certified) have ~55 HP loss through the drivetrain. That puts you at 625 HP. If your peak HP RPM is higher than stock, add another 5 HP. Add another 5 HP for additional loss through the differential gears and that puts you at ~635 FWHP."

Thes LS7's horsepower is at the flywheel, and if there is a 55 Hp through the drivetrain, then you would have 450 HP at the rear wheels, not 625 HP. He keeps adding to the amount for the additional horsepower losses instead of subtracting.

FloydSummerOf68

Who is everyone?

I've never seen someone say 25%

corvette4595

My LS3 A6 just dynoed at 370rwhp. Assuming GM rates the engines accurately (430hp), thats a 13.9% loss.

HOXXOH

GM rates HP per the standardized specification that has accurately defined and controlled temperature, humidity, and atmospheric pressure. So any comparison of chassis dyno results need either the exact same conditions or have standard corrections to match the same specifications as GM uses.

Other factors to consider are whether your pull was in 4th gear (1.15 to 1) or 5th gear (.85 to 1), with or without converter lockup, if the results compensated for axle gear, and even how much wear and air pressure your tires had.

Understanding the close tolerances and repeatability of today's manufacturing methods, easily leads me to believe that any engine picked off the assembly line will produce well within 1% of the rating of the test engine used to establish the original advertised HP.

However, variations can vary far more between chassis dynos with the identical car and even with the same dyno on different days.

GM rates HP more accurately and with extreme repeatability. So the only assumption that can be made, is that of the accuracy of the chassis dyno results.

4SELLL

I think the converter itself makes a difference, unlocked a difference, I wonder if the tune or having the trans built or not would? Also wonder what how changing rear end ratio would affect it. I went from 2.56 to 3.42.

LS1LT1

Rear axle ratio can effect the dyno numbers for sure, all else being equal a car with a 3.42 rear would almost certainly read at least a little lower than one with a 2.56.

ganador01

Dyno's don't work like that . You use a gear that allows you to get a good run out of the engine. The gear ratio is irrelevant and does not effect the outcome of your run. On the dragstrip it does, on the dyno it doesn't. Look at it this way. Does gearing increase horsepower or tq? No, gearing reduces or increases load on the engine/drivetrain. Gearing does not create or remove power.

Fordracer9

Gear ratios have nothing to do with the power the engine makes, and have close to zero effect on a dyno pull. Dynos measure power by how long it takes to accelerate a known mass to whatever speed as compared to engine RPM. The only thing changing gear ratio will do is either increase time to a higher speed, or decrease time to a lower speed. The computer will then use those numbers to calculate HPand TQ to fit the speed/time.

I've seen WAY more variation in dyno results from tire pressure variables or where the car was strapped down on the rollers.

4SELLL

[ The only thing changing gear ratio will do is either increase time to a higher speed, or decrease time to a lower speed. The computer will then use those numbers to calculate HPand TQ to fit the speed/time.]

This is the what made me wonder about car with a big gear. The pull is over so quickly i thought it could have some effect.

0Bobby @ LG Motorsports

The dyno does need a 1:1 for correct data and deeper geared cars do change numbers for sure.