There are a number of companies who make performance TH350's and TH400's. TCI and B&M come to mind, among many others. I think the 350 and 400 can be built to take just about anything you can throw at them, if you have the cash. If you go to a local dragstrip and ask some of the competitors, they should be able to point you to local shops that do performance work.
I'm also trying to figure out what to put behind my engine, when I build the new one. The three possibilities seem to be a TH350/400 with an external overdrive, or a 200-4R/700-R4 overdrive automatic, or a 4L80E overdrive automatic.
The 200-4R/700-R4 transmissions do seem to have a torque problem. I'm not quite sure exactly how much torque they can reasonably be built to survive (I've heard a lot of conflicting numbers). On the plus side, they have very good gear ratios.
The Th350/400 with external overdrive will take a lot of torque, but the gear ratios aren't as good as the overdrive trannies. Neither the overdrive or the first gear will be as good as either of them, so you'll end up having to make more torque to compensate for the gearing difference. I'm not certain, but I believe the gearing can be reworked, if you have the money (although it still won't match the 200-4R overdrive ratio, or the 700-R4 first gear). On the plus side, I've been looking into some things, and I believe that this setup could be worked to operate similar to a stick shift, with manual shifting and an traditional "H-pattern"-type shifter. It would be a manual, but without the clutch, in many ways. It's all just theoretical, now, but there's no reason why it shouldn't work. I'm also looking into the possibility of mounting the GV overdrive unit to the front of the differential, instead of the rear of the transmission, which should give a better weight distribution and take some stress off the driveshaft. The biggest plus of the external overdrive setup, in my opinion, is that it gives you better ratio splits - six speeds instead of three. Closer ratios are a good thing
And here they are (with percentage differences):
TH350
2.52
1.97 (78%)
1.52 (77.2%)
1.19 (78%)
1 (84%)
.78 (78%)
TH400
2.48
1.93 (78%)
1.48 (76.7%)
1.15 (78%)
1 (87.0%)
.78 (78%)
TH400 (assuming that it can be re-geared to have a 2.75 first and 1.57 second gear)
2.75
2.15 (78%)
1.57 (73.0%)
1.22 (78%)
1 (82.0%)
.78 (78%)
(for comparison, the ratio splits on the stock TH350 and TH400 are around 60% for 1-2 and around 65% and 67% for 2-3)
The third option would be my choice, due to the more aggressive first gear. It would also be more expensive, due to the cost of re-gearing.
The 4L80E is an overdrive version of the TH400. I haven't looked into it too deeply, yet, but it's a pretty serious piece of hardware, from what I can tell. It's overdrive is only .75 (as opposed to .70 for the 700-R4, or .67 for the 200-4R) (better than the .78 for the GV unit), so you can't run quite as aggressive rear gearing, but it's supposed to be bulletproof, and I know that it can be re-geared to have a 2.75 first gear and 1.57 second gear (same as the 200-4R). Of course, it won't be actually as aggressive in overall gearing as the 200-4R, since the rear gear will be limited by the overdrive ratio, so those gears won't see the same multiplication factor (you could run 4.11's with a 200-4R and not be running as high rpms in overdrive as you would with the 4L80E will with 3.70's)
To illustrate that:
200-4R with 4.11's: 11.26:1, 6.45:1, 4.11:1, 2.75:1
stock 4L80E with 3.70's: 9.18:1, 5.48:1, 3.70:1, 2.78:1
modified 4L80E with 3.70's: 10.18:1, 5.8:1, 3.70:1, 2.78:1
But, as before, the 4L80E can take a lot more torque than the 200-4R, so as long as you can make enough extra torque to compensate (11-18%, depending on whether you use modified or stock gearing), you're golden. On the other hand, you'll have to build a more powerful motor to make the torque difference happen, and plan on a higher powerband, which will add expense both in the initial build and at the pump.
I can't really make a recommendation, since I haven't even decided, myself. But these are some of the issues that have come up during my search, so maybe they can help you figure out what will best meet your needs. I
am sort of leaning toward the GV unit, myself, but only because of my ideas about re-working a transmission for the H-pattern manual shifting, and mounting the GV unit to the differential. If those ideas don't pan out, then I'd probably start leaning towards the 4L80E.
The 4L80E is also probably cheaper than a performance TH350/400
and GV unit, and would be simpler to install, IMO.
So, there you have it, for now.
Joe
