Paul 400's will take a lot, with your hp range you have no worries. Just make sure it's rebuilt by someone who knows what they're doing and uses good parts (ask around do some homework). Probably a shift kit to firm up the shifts and something like a 2500 stall converter if you have a mild to medium cam would be good...Dave

 

TH400's can take more than the average Joe will ever throw at it.

One of our members here, Jakeshoe, can hook you up with a pretty stout piece. He goes out of his way for customer service too!!

Here is his website - http://www.jakesperformance.com/

 

Somewhere in my memory tells me the factory rating on a TH400 was 740 Ft. Lbs. The advantage of any automatic is the planetary gear set which provides numerous points of gear-to-gear contact instead of just 2 or 3.

The weak point of the TH400 is spinning the sprags during a burn out to an RPM they were not designed for. The stock parts were fine for their original intent, but not for high RPM, meaning you should replace them with an aftermarket lighter clutch drum and heavier sprag assy. for high RPM usage.

I had a friend with a 396 Caprice that would rev the engine too 6000 RPM, and pull TH400into first gear. He ran at the drags like that for a year and a half before something broke. With a stock TH400.

Hopefully, someone will give a better answer than mine.

 

Get a good intermediate sprag installed, performance frictions and steels, and a manual valve body if you don't mind shifting. As for the converter that will need to be matched to the new engine and your intended usage.