So after all my launches on this stock 4l60e with the slicks on, it’s starting to slip quite a bit, I’ve been looking at a kit from Oregon Performance Transmissions for about $1700 to get it all done up (parts only). But I’m looking at TH400s now because of the cheaper rebuilds and the fact that they’re a million times stronger. After alls said and done, down the road I’m looking for it to handle about 700hp. And I’m fine with losing out on the OD. So what I’m wondering is what can I expect cost wise to put a TH400 in the car to meet these goals. And what can I expect to have to do? Is it even worth it?

 

I can offer some input, but don't know if it will be applicable to your needs. My build was pretty much strictly for drag racing (although it was fun to drive on the street). The engine dyno w/ 2 stages of nitrous (~265 HP) yielded a peak torque of 770 lb-ft @5,000 RPM. We later stepped the nitrous up by another ~30 HP, which probably put the peak torque very close to 800 lb-ft. New owner has best run of 9.647 @ 139.41 MPH on a 250-shot. He did upgrade the intake manifold and camshaft, to pick up about 50 N/A HP over my build.

Race Prepped rebuilt TH400
B&M SFI-rated flex-plate
ATI Non-locking torque converter
JW Ultra Bell bell housing
ATI reverse pattern fully manual valve body
B&M Pro-Ratchet shifter, mounted to fit in stock 6-speed console
TCI SFI-rated Case Shield
Perma-Cool Fan assisted trans fluid cooler (my Griffin radiator did not have a trans cooler)
Lokar Dipstick
GM deep trans pan with drain plug added
Fluid temperature sensor/A-pillar gauge
Gear Vendors 0.78:1 Overdrive (essential on the street, running 4.11:1 gears in Strange 12 bolt)
Shortened driveshaft - Mark Williams 3" chrome-moly
Modified transmission cross-member (for short output shaft housing). Don't remember if we started with my T56 cross-member, or used an A4 cross-member. (picture available)

This was done 20+ years ago, so the costs would not reflect current pricing. The engine builder came up with the trans from someone ("Gene") in eastern PA. Back then is was just under $1,000.