im a noob with my car... but from what i have heard you loose ~ to 15 % hp on A4s ... is there way i can make that percentage lower with fairly inexpensive mods

 

The driveline losses you hear people alk about with automatics are largely in the context of race type torque converters which are "loose" (have much higher stall speeds than the stocker) and usually do not have the lockup function of the stock converter. If you have a stock converter, once it locks up you will have about the same driveline loss as a manny tranny car. Prior to lockup, you will be losing an additional couple of percent due to converter slippage. This is inevitable when a fluid coupler like a TC is used, there's nothing you can do about it. The stock converter is about as tight (efficient) as they make 'em, so any converter swap would likely increase the losses (until lockup) though might actually provide better performance due to torque multiplication and getting the engine into the power band quicker.

Rich

 

when does the torque converter "lock up"

 

It's controlled by the PCM ("computer"). If you pay attention when driving, you can feel it/see it by watching the tach. Accelerate on a level road up to 50-60mph and note that after it upshifts into high (4th) if you ease off the throttle after a few seconds the revs will drop a couple of hundred rpm - that's when the converter locks up. Gently open the throttle more and more and you will see the revs jump up when the converter unlocks. The PCM "knows" you want to accelerate so it unlocks the conveter. At cruise, it is locked up to maximize fuel economy.

Rich

 

ohh, i know what you are saying .... so from your first post you said that the torque converters now were effecitant enough, but there is still some room for slight improvment. would you put a new one if you had my A4?

 

As Rich said, there is really nothing you can do about it. Automatics are made to slip-that's what they do (before converter lockup).
In a straight race comparison with a manual, the auto makes up for the difference in faster and more consistent shifting. This is why most serious race cars have automatics.

 

thanks for all of your input

 

On a dyno the number for all drivetrain loss on a automatic
is between 20 and 25%. Your number is more for a M6 manual. There is a big difference between Flywheel (mfg numbers) and actual Rear wheel horsepower (RWHP) the car is putting to the ground. And NO there is no inexpensive Mods to correct this.

 

Those numbers for driveline loss are high. Don't forget, he's talking about a stock converter, not an aftermarket converter with a much higher stall speed than a stocker. Unfortunately, higher stall speed pretty much equates to more hp loss due to "slippage" of the converter.

When a lockup converter is used, once the converter is locked up, you would expect essentailly no difference in RWHP between a manual and an automatic. The interesting thing is, locking up the converter early will slow the car down (in a drag race) as the torque multiplication is lost and the engine may be pulled down below its' power band. Hi-po drag cars using automatics don't have lockup converters. There are a number of reasons for this, but the most relevant is that it wouldn't really result in a performance improvement.

On the chassis dyno, a stock or near stock 4th gen will show 10-15hp less with an A4 compared to an M6. The best numbers are seen with the A4 in 3rd and the M6 in fourth. Your quiz for the day is to answer why these gears give the best results.

Rich

 

They are both in a 1 to 1 situation (direct), no under or overdrive. This gives the least amount horsepower loss, due to less drag.

 

Also, using a 1:1 ratio keeps dyno results consistant, since it's a constant variable, and you can accurately compare between auto and standard, and even between brands (just about all manufacturers have a 1:1 ratio in their transmissions, whether it's Ford, Dodge, Honda, etc.).

Unfortunately, there's really nothing that can be done to eliminate or reduce drivetrain loss. In many cases, the more performance oriented you make your car, the more loss you'll see, but the net result at the end of the day should still be more power and more speed.

AND, you can always cry "high drivetrain loss" when you get low dyno #'s!! Like my car, which "only" put 289 HP/307 Tq at the wheels, but I still maintain that it's ~350 HP at the motor!

 

Even at a 1 to 1 ratio, you cannot compare an automatic to a stick (on the dyno) due to the torque converter and the many differences in torque converters themselves, stall, str, diameter, etc. If you lock the TC up, now you will have the pumping losses of the automatic, which will always "eat" more HP than a stick. How many times have you seen an automatic on the dyno come up with lower numbers, and yet run just as fast if not faster at the drag strip. Torque multiplication in a properly designed torque converter, can & will make the automatic quicker & faster in the quarter mile.

 

I guess what I was trying to get at is the consistancy of using 1:1 --- that it's not a variable. I realize autos still eat more power than standards in 3rd (1:1 gear), but I'm sure if you ran in 2nd gear or something like that, the dyno #'s would probably look great (or maybe worse, I dunno?? ) but using 1:1 is always the same. I mean, if you said to do the dyno run in 2nd gear, that would be a 1.52 ratio for a TH350, but a 1.48 for a TH400, right? Suddenly there are way too many variables getting in the way, that there's no hope of accurate comparison between different cars / setups / etc.