Can anyone explain exactly what a torque converter does? i know a little about this subject but not much. i know there are aftermarket kits for this but i hear you can just install a kit and do it yourself. does anyone know of a tech link or can explain what this does. i checked the tech boards bt didn't find anything that i was looking for. thanks

 

Torque converters work like a turbine engine operating in a fluid medium instead of air. Essentially the engine is connected to the input side of the converter and provides the power that spins it. This spinning motion is transfered to the transmission fluid inside the converter, and causes the output side of the converter to begin to spin, imparting motion to the transmission and allowing the car to move.

The tricky part is when people start talking about stall speed. This is always accompanied by a number (e.g. 2,400). What this means is that at the given RPM the converter is said to have achieved a "perfect coupling", meaning that there is no slippage through the converter. Below this point fluid shear allows the input side to turn faster than the output side, meaning that the transmission is not recieving the full rotational power of the engine. However, a manufacturers given stall speed is really more of a guideline than an actual accuirate number. Engine size, camshaft selection, vehicle weight, rear gear ratio, and other variables can alter the observed stall speed of a given converter. It is always best to talk to a manufacturers rep, or people with similar combinations to yours to determine where the actual stall will be.

As far as DIY kits for auto transmissions there are several. Common mods are higher stall converters, shift kits, and bigger servos. Changing converters couldn't be simpler. You remove the trans, pull the converter, and swap it for one with a different stall.

Shift kits are trickier, requiring you to drop the pan and make a few modifications to the the valvebody. If you follow the directions closely these kits are also fairly straightforward to install, though you will wind up with trans fluid absolutely everywhere!

Bigger servos are used to increase the apply area of the servo, which in essence just means that the trans will be more resistant to slipping under increased power. The Corvette servo is a common upgrade for the 700R4. If you do a search on this board you will easily find the GM PN for it.

Automatics are pretty complicated, but I have found that you don't need to know how they work to modify them successfully. You just need to know what happens when you change certain parts. Of course knowledge is always power, so if you're interested read up on auto transmissions in some of the books readily available on the subject.

 

what advantage would a higher stall converter give you? also i heard about a way to use a switch to manually switch it one and off? i don't know if this is true or not, but what is your take on that? also is a shift kit worth the money? they are realtively cheap. my buddy had his valvebody drilled out at a local tranny shop and he loves the results. thanks for the explaination on the torque converters. that was an awesome answer! thanks man!

 

Here is another pretty good read on converters. Hope it works...

http://www.mtfba.org/tech/converterarticle.htm

What a higher stall will do is allow the motor to "flash" to a higher point. If you have say a 3500 RPM stall TC, then when you punch the gas it will flash to that rpm and stay there until everything catches up. Basically in drag racing, its like a 3500 rpm clutch dump. It gets you into the powerband a ton quicker, thus why 60's are dramatically decreased w/ aftermarket converters.

 

A higher stall converter has a higher point at which the converter achieves a "perfect coupling" or "lockup". This allows the engine to rev higher in the RPM range and closer to peak torque, before the converter effectively locks and the engine must rev while being ridgidly connected to the driveline, in effect having to accelerate all of the mass in the driveline as the engine accelerates, instead of having to move only a fraction of that mass while accelerating, like before the stall apeed is achieved. Using a higher stall converter, even on an otherwise stock car can easily trim .5 seconds off your ET in the 1/4 mile. You will need to upgrade to an external trans cooler though, because the higher stall converter will generate a lot more heat than a stock converter, and heat is what kills automatic transmissions.

The switch you have heard of is for a "lockup converter". A lockup converter uses a seperate mechanism, namely a lockup clutch, to physically lock the two halves of the converter together at highway speed in 3rd and/or 4th gear in order to get better gas mileage (no power wasted in converter slippage). I don't really see the benefit of this, because in 3rd gear at WOT the converter isn't locked, and the trans won't upshift into 4th at WOT unless it has been modified. Basically the lockup function is only for gas mileage, nothing more, and isn't a hinderance to performance.