Topic: Fucking Torque Converters, How Do They Work?!
So, torque converters. I kind of understand their basic function, but, I guess my question is more 'how do I 'optimize' one for endurance racing'? (TL:DR - Do I generally want the lowest stall possible, and, can I actually count on a lockup clutch?)
The 4T60E in the Buick is showing some serious signs of degradation - I'm genuinely impressed that it's still holding on, coming from a car with 88k miles on it, adding several thousand more race miles, and heating it to the upper-end of the 200 range several times trying to get our ATF cooler in order. And, to its credit, it still shifts pretty well. But, it makes a pretty horrible rattly sound, and the fluid after the last few races (where we didn't even race the whole race) has been awfully dark and burnt smelling, so, preparing for the eventuality of a replacement. And, while a used transmission is fine, I'd just as soon buy a new torque converter
What am I looking for in a torque converter? I'm going to spring for a new one, but, want to make sure my logic is sound. I've read a decent bit about stall speeds, but, it's almost all geared towards drag racing. Honestly, as long as Dale doesn't have to push the car to help it get going from the driver check, I couldn't care less how it takes off. Am I correct in the assumption that, for what we're doing, and given the constraints of this transmission, a low stall is good? Stock, I believe we're in the 2000-2100rpm stall range - and, since we've removed weight and added power, I think it's effectively even higher than that. The same transmission, hooked up to a larger, heavier (by 400-500lbs) Park Avenue, with more power (3800 NA & S/C) got a ~1400rpm stall, which I believe is as low as they went from the factory. That's probably a pretty safe bet, right? We're actually making the same power as an NA 3800 now (cheaty, I know), weighing now even more less than a stock PA, so, I can't see that being a problem. Should I try for lower? As far as I can tell, it's a GM 245mm/9.75" torque converter, so, parts should swap in (Sonnax lists a whole catalog of stuff for it).
The big thing I'm looking for is reduction in heat buildup - we have a good sized cooler on it, with a dedicated pusher fan, that takes the hot fluid and gets it nice and cool again, but, still the transmission gets hot. Everyone else who races 4T60s says they just don't flow enough fluid through the cooler to really cool themselves at full duty, and they also really, really don't like running hot. At Road Atlanta last month, temps in the 50s, wet (so can't push it quite as hard as you'd like), transmission fluid is still running 200-210. Add another 30-40 degrees of ambient temperature, a stickier track, and you're quickly into 'this thing is too hot' territory. I don't want to make the car practically undriveable or sacrifice a ton of speed, but, swapping to a much lower stall converter seems like it should reduce heat, and probably won't affect driveability/speed too much, since we don't do a lot of 'taking off'.
The other thought is, you can wire in a lockup switch for these cars relatively easily. But, is that just asking for trouble? Barring the fact that you'd have to remember to turn it off before you stop, do those things fail often? And, if they fail, do they cause problems, or do they just kinda quit working? Not looking to add extra problems, but, essentially bypassing the torque converter altogether and eliminating that huge source of heat sounds great. I would be so nice not to have to agonize over this damned transmission fluid temperature every race.
1996 Buick Century - we upgraded our crappy GM sedan with parts from a crappy GM minivan.
"It's got a van motor, a 220 cubic inch plant, it's got van tires, van suspension, van shocks. It's a model with the catalytic converters ripped out so
it'll run good on regular gas. What do you say, is it a racecar or what?" - Blues Brothers, Probably