MCR

As you push near 350-400 hp the transmission on this car won't hold up.

What is the best automatic transmission you can upgrade to?

Tele-Caster

Well, maybe a stock 4R70 won't, but the 4R70 can be built to support well over 500 hp reliably.

Things like harder intermediate shafts, 8 clutch pack direct clutch drums, 2" wide Kevlar O.D. bands, HD torque converter, etc, can be applied to the 4R70 to make it survive more power than you're likely to try to feed through it with a pushrod Ford V6.

A lot of people think that stuffing electric 4R70 guts in a non-electric AOD / 4R70 case is an upgrade and one capable of living a happy life behind 550 hp.

I think the 4R70 is tougher than some give it credit for and it can be made even tougher still. The Hi Po parts are available to do it. I wouldn't be inclined to ditch it because contrary to the OP's assertion, one can be built to handle some pretty monumental power gains.

BabyGT

Yeah it can be built, which basically means gutted and replaced with completely different internals, at that point the only thing left that should really consider it a 4r70w is the shell.

Tele-Caster

From an engineering standpoint, the notion that complete gutting and replacement of all internals of an electronic 4R70 to support the HP level the OP mentioned is hyperbole.

I'm currently having a performance automatic transmission specialist build me a 4R70 in preparation for the upcoming 2015 autocross season. They claim that the end result will be good for up to 550hp. The finished product isn't going to be "gutted and replaced with completely different internals" as the quoted poster asserts. It's a basic performance auto trans build; nothing more, nothing less.

Cost to me is a little over $100.00 for the junkyard core from a '99 that the shop is building from plus their $2,000.00 in parts and labor. That's not megabucks for a transmission that will handle more power than a pushrod 3.8 Ford V6 is likely to muster outside of fantasies and dreams.

BabyGT

What's basic that will do anything for the amount of power it can handle?

I'd call basic a shift kit, a tuner, and maybe a ratchet shifter, when you start talking about things that require the trans to be pulled and the internals removed, even if some go back in, that's hardly basic.

Its not quite considered built if its something basic done.

That's like calling a v6 with an intake an a new muffler built. Replacing half the internals is hardly a basic build. For that matter for 2g's you could pick up a built c series trans that will hold much more torque.