What needs to be done to a th350 so it will survive behind the 6.0 vortec I'm going to swap in?
Is a rebuild kit from Hughes or TCI enough or are new components like hd drums etc needed?
What stall speed is recommended?

judging by your loaction i'm gonna take a wild guess and say that this is gonna be in a formula offroad rig. am i correct?

i would say that the th350 should hold up just fine as long as you run a good converter and cooler. they're actually pretty strong transmissions and are much smaller and a bit lighter than the th400.
of course the longevity of the transmissions life will all depend on vehicle weight, tire size, axle and t-case gearing, converter stall, driving style,........

No formula offroad, just my full body 3700lbs cruiser with volvo portals, 39.5" TSL.
So 375 lbs-ft wont be a problem for a stock th350?
Is it worth getting a rebuild kit with alto red eagle clutches and kolene steels?
What converter would you recommend?

i think with that drivetrain setup you're gonna be just fine. i'd be more worried about the volvos holding up than the th350 failing.
the oh kit with the red devils and kolene steels would be a nice way to go. i'd install the small transgo shift kit as well. don't go too crazy on it though. art carr makes a good converter as far as the mass produced stuff goes. i would NOT recommend a B&M. they just plain suck.

I spoke to a tranny builder and the guy said that hd sprags are mandatory.
What I didn't understand is if you need to change both sprags to hd ones or only the intermediate sprag?

You would probably want to get a stall speed that is pretty low.


I got a TCI 13in for my 406. :p

Why not use a short shaft 400? not much more weight.. but a lot more strength.

Why not use a short shaft 400? not much more weight.. but a lot more strength.


no matter what "shaft" style 400 you use, it's still almost 4" longer and a bit heavier than a 350. in a cruiser you needf all the rear driveline length you can get.

I spoke to a tranny builder and the guy said that hd sprags are mandatory.
What I didn't understand is if you need to change both sprags to hd ones or only the intermediate sprag?


hd intermediate sprag and race is really all you'd need. you can upgrade the low sprag to the th700 style model but that involves replacing a few components.
also, make sure your th350 had the "V8 style" drums, they hold more clutches than the 6 banger stuff.