C5XTASY

Question pretty well says it. I've been told Y-body transmission losses are about 15% for an M6 and about 20% for an A4. I realize gearing has some effect, as would greater rpm, but do not understand why power and torque loss would be greatly affected by increasing the total engine output. Therefore, I was wondering if it's rather closer to a fixed loss (at max power and torque) rather than a percentage of whatever total your engine is capable of producing. All thoughts and opinions welcome, but if anyone has any documented evidence one way or the other, it would be really appreciated also. Thanks!
Ed

FAST FREDDY

its a %

john kilgore

l think if you think about it you'll see that it always takes more power to do any amount of work if it is done quickly.

C5XTASY

I understand that. What I'm asking is why. What I don't understand is where the extra power and torque is being consumed. How would rotating gears at a greater rate of acceleration, or increasing hydraulic pressure at a greater rate, cause losses directly proportional to that rate? Frictional losses would cause some increased losses via btu production, but hard for me to believe that drivetrain loss increases as a direct percentage of rate of acceleration, no matter what that rate is. Perhaps it's impossible to measure without bench dynoing the motor out, and then in, the car. And then, repeating that procedure after modifying the motor. Sure would be interesting, though.
Ed

BlackHawk T/A

iTrader: (3)

Just do a simple comparison...look at high HP cars...like George Baxters 1100hp 383 LT1 making 800-900 to the wheels. Compare it to your daily LS1, 350rwhp which makes around 400 at the crank. There's your answer.

jimmyblue

iTrader: (11)

There are loss components that vary purely with RPM, and
speed, and there are those that vary with load.
For example, the gear-in-oil loss in the rear end will be purely
MPH. The rear gear scrub losses in the hypoid gears will vary
with load however. And your 9" drag car will differ from your
skinny 10-bolt, in both (bigger gear radius in the soup, more
drag torque; more off-center, more drag).

The A4 takes shaft power to spin the oil pump and the
pressure head is varied with load, so you have a loss that
depends on both load and RPM.

Thye A4 converter used on a big power car, you can bet will
be well different in stall speed and efficiency from a stocker
or a "street performance" bolt-on car. Easily 5%, maybe 10%
loss in efficiency right there if you go from a 3000 to a 4000
stall speed. Efficiency becomes peakier as well, another point
of variability.

So much for rules of thumb.

chris718

johns statement is true.most of us have been led to believe that with a given weight of rotating internal components and frictional losses that regardless of input torque or horsepower it will take the same amount of energy to spin them up and complete power transmission.dynamometer results have proven this to be incorrect due to other variables at work.the engines ability to gain rpm against the transmission ,final drive,tires,resistance and vehicle weight,extended rpm needed to produce extra power,component spin up time ,converter and inertia etc all increase horsepower and frictional losses created and consumed before exiting the output shaft as usable power.i have seen this power loss ratio to be not as biased towards higher horsepower losses as power goes up with the 2004r verses the th400 however.this produced confusion for me after spending some time on a chassis dyno before i had time to think about why.

john kilgore

also if it helps, the power loss is directed connected to time. time is your killer, if you cut the time in half that you are in first gear the power loss might be squared. in other words if you cut the time in half the power loss could be squared(5hp squared or 25hp). but sometimes more rear end gear makes up for the loss because your car moves easier.