A stall converter is a torque converter with a higher rpm launch ability for an automatic transmission. Guys with manual transmissions can rev up their cars really high and drop the clutch for a super hard launch. Automatics don't have that luxury with the stock torque converter, so getting a converter that revs higher at launch is the way to go for much quicker starts.
The stock torque converter flashes to about 2300 rpm's if you mash the gas pedal. A stall converter that flashes to about 3000 to 3200 rpm's is a good street/strip upgrade, but our heavy cars really need a bit more to really launch hard. 3400 to 3600 rpm converters are really about perfect for entertaining street/strip cars, while maintaining decent fuel economy. I bought one rated for 3600 rpm's (in a stock GT). Once you start adding horsepower, though, the rpm's that it flashes it will go up. So, with just a CAI & tune, my was flashing to 3800 rpm's. Added the supercharger and it now flashes to 4800 rpm's making for a very aggressive launch (just like a guy with a manual trans revving to 4800 rpm's and dumping the clutch).
Keep in mind that if you take off with partial throttle, the car won't rev as high. The flash speeds I mentioned above are only at wide open throttle. So, the car will feel normal at light throttle, but is a beast when you mash the pedal to the floor. Wide open throttle shifts are better, too, as rpm's never fall below the flash speed (unlike a manual trans when you lift off the gas to shift and lose rpm's - and boost with a blower/turbo).
To preserve fuel economy, select a stall converter with a lock-up feature. The factory torque converter locks up in 4th and 5th gears (with an internal clutch in the converter) to get better mileage at highway speeds. Low gears don't need the lock-up as you want the converter loose to rev higher for better acceleration. Too loose all the time, though, generates heat which is harder on the trans. So, a bigger trans cooler is a great idea with bigger stall speeds.
Hope this info gets you started. Anyone with an automatic who drag races or wants a more aggressive daily driver should get an aftermarket stall converter. Mine dropped 3 tenths of a second off my 60', 330', and 1/8 mile ET's at the dragstrip and made the car so much funner to drive. Got more performance gain from the converter than the 4.10 gears (and for about the same money).
With an automatic transmission, when you floor the gas pedal, the rpm that the engine zips up to before the car starts accelerating is the flash point. High rpm stall converters offer so much performance because they flash to a higher rpm, allowing the car to instantly rev to the sweet spot of the powerband. Ideally, you want it to flash to just a few hundred rpm's below the point where your engine makes peak torque (4,500 rpm's in a stock S197 GT).
DO NOT FEAR THE GEAR ........Some of the older New Edge guys might get that lol
Seriously though, I've seen a hundred of these threads(3.73s v. 4.10s)...bottom line, how many people do you see(do a seach) who wish they didn't go 4.10s instead of 3.73's, very few now look how many who "eh, kinda wish, if I could do it all over again, etc" went 3.73s now wishing for 4.10s
You WILL loose a little on the highway....thats just b/c you are going to be rev'n higher at 70/whatever....but other than that, the MPGs will be all up to you and how heavy your foot gets
You will get better MPGs in the city if you just stay out of it....I see your manual, start out in 2nd, 3rd, 5th, etc. you WILL get better milaege in town if you can stay out of it with 4.10s....But whats the fun in that
Not meaning to jack the thread, but are 4.10s on a supercharged car all that necessary like in an NA? I find my 1st gear to be quite short and no traction what so ever as is.
My goal is to improve performance from the taller gears; 3rd, 4th, and 5th; making the RPMs move a little quicker and stronger.
So would it be more beneficial to just increase horsepower and torque and keep the 3.55 gears instead of going with 4.10s? My car is a DD and I do a lot of highway driving. Plus I also do autocross which I have issues coming out of the corners too hot...
Not meaning to jack the thread, but are 4.10s on a supercharged car all that necessary like in an NA? I find my 1st gear to be quite short and no traction what so ever as is.
My goal is to improve performance from the taller gears; 3rd, 4th, and 5th; making the RPMs move a little quicker and stronger.
So would it be more beneficial to just increase horsepower and torque and keep the 3.55 gears instead of going with 4.10s? My car is a DD and I do a lot of highway driving. Plus I also do autocross which I have issues coming out of the corners too hot...
With your roots type blower, you already have good low end torque so you wouldn't benefit from 4.10's as much as an NA car or one with a centrifugal blower. However, you will still benefit some - especially by tightening 3rd, 4th, and 5th that you mentioned specifically.
However, for autocrossing, I would suggest keeping the 3.55's (and adding hp & tq as you noted) so that you don't need to shift up & down as frequently. If you were going to primarily be drag racing, I'd suggest going with 4.10's.
Looks like should stick with the 3.55's from what you've described as your intended use of the car. Hope that helps.