ALLEGRO

Was chatting with another car-buff this weekend, and we got into the conversation about there being a difference in torque between the manual and auto transmissions. We all know the figures (350 vs 375), but for life of me I could NOT remember the ACTUAL reason for the difference.

Who's got it?

momo20

Typically a manual car has a bit more torque than an ATX. The mechanical connection of a standard tranny provides more 'grip' than the fluid pressure in a torque converter.

Jistari

Another way to say it is that there is just "less loss" of torque between the crank and the differential through a manual.

TotaledmyGN

I don't think the op was talking about rwhp. where a manual trans. is more efficient. He is asking why there is a difference in engine ratings. Camshaft???

Vetteman Jack

But I think that is what the above two are talking about too. Could be wrong though.

Cybermind

Actually, the engine itself has a different rating. We are not talking RW torque. The LS1 for the manual car is rated at 375 ft/lbs vs 350 ft/lbs for the auto. It could be that the auto LS1 has been slightly detuned to improve driveability and transmission reliability?

Polar Jet

In defence of the auto, the torque rating did go up from 350 to 360 on the 01-04 models.

ALLEGRO

Well you all have fallen into the crack I got in this weekend. The posted value for HP and TQ are NOT rear-wheel measurments, rather static engine related figures.

We too could not remember exactly what the difference was......


NEXT ?

jbondfl

Chuck from COW should be able to help out here since he's the apparent king of tuning A4's.

I know on my '03 Yukon one of the HUGE performance killers was the computerized torque management system that was intended to make the transmission last longer. There's a good chance that is what the difference is here as well.

dougbfresh

Who cares, it was a tiny difference anyway.

AU N EGL

That is the main reason

have seen ATX tuned to 360 ft lbs with better air intake an headers

ALLEGRO

It was only a topic of friendly "car talk" conversation. As far as it being a tiny difference, a lot of engineers would argue that 25 pound-feet or torque is NOT a tiny amount.

MawneeC5

The wieght difference between the flywheel and flexplate?

Dominic Toretto

IDK but, I would guess the difference would be in the tuning of the transmission(A4) itself. While both LS1s make the same power, Chevrolet probably detuned the A4 slightly to be more reliable by not using as much torque.

-Alex

ALLEGRO

All I can think of is just tuning. Nothing else seem accurate.

0Chuck CoW

I think what it boils down to is that, quite simply, it takes slightly more power to turn the drivetrain, from the flywheel back, in an automatic.

Or.... The standard trans drivetrain takes less power to turn....

While both system have "mechanical losses" between the flywheel horsepower and the tire contacting the road...The automatics have slightly more loss... It's only a few percent...but it's there.

For instance a standard shift clutch system couples tight when engaged and, assuming NO SLIP, transfers nearly 100% of the engine's torque to the driveshaft.

On the other hand, a torque converter in an automatic, generates tons of heat from the frictional losses in the converter when the fluid is
sheared to propel the car, and WHAT IS HEAT???

Heat is ENERGY LOST. Simple. Automatics generate much more heat than standard shift cars and cost you a bit of power. There are
likely other small losses, but I believe that the largest losses occur in the torque converter.

This is NOT a reason to buy a stick over an Automatic. Some of the fastest cars are automatics and when programmed correctly, they're
MORE fun in my opinion.

That's about the story.
Chuck CoW

Jistari

Well when I read the bolded section above, what popped into my (sometimes malfunctioning) head was the analogy of drive train power loss, best explained by COW above, exactly it....if it makes more heat it has to use energy to do that that the one that doesnt make as much heat has to transfer somewhere....like the wheels.

But . . .I didnt know about the engines themselves being rated at different HP/Torque ratings at the crank, thats new information to me.....Thanks

XDodgeMan

Flywheel horsepower and torque have nothing to do with what goes behind the engine, this is the number that is advertised. Rear wheel horsepower does care what happens behind the engine.

Auto trans takes power to run so rear wheel horsepower would be down but that is not what is advertised. Weight of drive-train components has no effect on power but they do have an effect on acceleration.

Torque converters actually increase torque at low speeds but overall they are usually slower due to losses with the the spinning parts, pumps, mass. Modern auto transmissions are getting very efficient with many speeds and lock-up torques converters.

I am guessing that the auto trans has some kind of problem with too much torque so the factory has an engine version (it could be just calibration) to limit torque to increase durability. This is very common in the auto industry.

rebelheart

The A4 equipped cars engines are detuned slightly in the interest of auto trans life(mostly for warranty purposes). This is measured at the crankshaft.

corvettebob1

Ding Ding we have a winner!