im building a pontiac 400 engine and its expected to have around 700 HP. i have an olds t350 with a shift kit and 3500 stal laying around im gonna try to use for a little while just aorund town until i can aford a t400. how long do you think this will last under hard driving? the rear end is a ford 9" with 4.11 gears.

im putting it in my 69 firebird, i plan on getting twin garrett hybrid t3/t4s by the endof next year to boost the hp up above 1000.

 

The th400 is stronger and is the better transmission for your application. Be sure you have the 34 element intermediate sprag, th400's built after 1971 use a roller clutch and can break even with mild 350 engines.

 

Even 700 HP can hurt a TH400 if it isn't properly built. You need a bunch of other stuff like a hardened input shaft. Get rid of the plastic thrust washers for some metal ones, more clutches etc. Spend the money and buy a properly built tranny to handle all that power.

If the engine is going to be putting out that much HP a 3800 stall converter is going to be a dog. Unless you're building a 500+ cid engine your torque is going to be way higher than 3800. You're probably going to need a stall closer to the 5000-6000 range with 4.56 gears to make it all work.

I wouldn't "expect" a 400 pontiac to have 700 hp until it's built and dynoed. 700 hp at 7000+ rpm won't do you any good on the street since the engine will never reach those rpms.