How much horsepower can a turbo 350 transmission handle

i have a freshly rebuilt stock th350 sitting in my garage and i was wondering if it would handle 450+ tq? if not what would i have to do to get it to handle that much? i have a 2500 stall on its way and would like the tranny to hold up. its going a street car but will see the track from time to time. thanks in advance

My TH350 is what I would consider a stock rebuild, just a B&M rebuild kit and no special parts, it has handled about 8 years of abuse, mostly 11 sec passes, a few nitrous passes in the 10's, and now the motor only has been in the 10's. I call that the limit for mine because I have to drive it back home so I don't want to break it. My motor made 520 tq on an engine dyno if that helps, but remember the trans is only as strong as the weakest part and these parts are over 30 years old now...

so say i rebuild it using a b&m rebuild kit and the only thing that is OE would be the housing i should be fine right?

so say i rebuild it using a b&m rebuild kit and the only thing that is OE would be the housing i should be fine right?

What about all the rotating parts like the gears, drums, shafts. Those dont get replaced during a rebuild unless broken. The rebuild kits usually only have the friction disc's, seals, and gaskets.

You will probably be ok just know that one guy can go for 15 years with a basic rebuild th350 and some may only last a short while, just depends who rebuilt it and how hard it was driven

Good luck

Rebuilt doesn't mean anything because there is a wide range of what work was actually performed and to what level of quality.
The weakest part of the TH350 is arguable the intermediate sprag. It would have been a good idea if you were rebuilding your automatic and knew what power you were putting it behind, to upgrade the weakest parts. There's other components that can be upgraded (clutch discs, input shaft) as well. It's cheaper to do it once than to have to do it twice.

Here's a good TH350 rebuild with how to pictures posted over at Nasty Z28. (Why don't we have stuff like this?)

i hope

people that come on this site , feel how lucky they are to have this vast amount of free information. Reading as many books as possible was all that was available 20-30 years ago.

21 years ago ,, i had some problems with a turbo 350 ,, so ,, i dug into it ,, by myself , had it down to the case ,, with no help , never did it before , I got a hold of an extra transmission in case i failed , so i had a back up plan , but i wanted to be able to do this , i did buy a book on a turbo 350 and got through it.

if i had a good turbo 350 , and was planning on abusing it , i'd definately get the sprag like was mentioned and the extra clutches put in.

i have a friend here that just had a TH350 rebuilt ,, i just about begged him to get a sprag for his ,, this one is going behind a 575 hp 454 in a full size truck ,, talk about having the deck stacked against you. They did put in extra clutches , it will be interesting to see how long it will last without the sprag ,,,, about the only saving grace it will have , is that its street driven and will never see a set of slicks

The guy in Paul's link is who built my transmission, super nice guy and really knows his stuff. I learned a lot just reading his posts on various bb's.

If you have a well built fresh th350 I wouldn't be afraid to use it, IF you aren't going to abuse it. Meaning correct burn out procedure, no downshifting at speed, keep it cool, etc. Maybe add a shift kit to firm it up a bit.

Jake did tell me for just a basic shift kit, he likes the Transgo the best.

I'm no expert, so take what I say for what it's worth, not much!

i do plan on adding a shift kit along with a heavier duty sprag. i will be doing burn outs lol but its mostly going to be street driven and once or twice at the track to see how fast it is.

TH350 upgrades needed to last.

The weakest Link in the trans is the intermediate "SPRAG RACE"
it is a affordable and easy to have changed.
http://www.summitracing.com/parts/TCI-328900/

Also a valve body modification is needed.

The kick down cable system on the TH350 has 2 functions. The first stage changes the forward pump pressure, the second change, the last 1/4 travel of the cable operates the downshift, (passing gear)
A mod to the valve body keeps pressure full and eliminates the Cable.

NOTE:
Not all TH350 are the same.
The 1-2 gear clutch pack for a 6cyc application will only have 4 clutches.
And drum change (or modification to current drum) to a 5 or 6 disc clutch.
This will help speed up the shift change and reduce heat and slippage.
The 2-3 shift system is strong,

With these 2 issues resolved the HP/TORQUE your looking to have will no issue.

Also using true "Type F" fluid will help the shift on the trans and have zero negative effect.

Al

what kind of mod to the valve body? like switching or removing one of the check balls?

what kind of mod to the valve body? like switching or removing one of the check balls?

I can not answer that.

My transmission guy can! But he always has his mouth shut!

he wants to be paid!

Al

i've

prolly put in ,, 3-4 of those B M shift improver plate deals ,, they do work ,,, one of them ,, worked REALLY good ,, it would shift extremely hard ,, none that i put that kit in ever had any trouble ,, the transmissions all lasted years after i put that kit in ,,,, why that one shifted so hard ,, i mean really hard ,, i don't know ,,

follow the directions and you'll be fine

what else is needed to beef up a TH350? might get my hands on a almost new th350 with pretty much new stock parts, it comes with everything, but i was wondering what is needed to beef one up?

Heat is the main killer of a transmission at any level.
Using the largest trans cooler possible can't hurt.
Keep an eye on your trans temperature and it should last a long time.
I've been pumping 500+ TQ thru my TH350 for 6 years with zero issues.
4,000 stall convertor

Heat is the main killer of a transmission at any level.
Using the largest trans cooler possible can't hurt.
Keep an eye on your trans temperature and it should last a long time.
I've been pumping 500+ TQ thru my TH350 for 6 years with zero issues.
4,000 stall convertor

I am having my TH350 built as we speak to hold 650HP. From what the guy told me, there are a bunch of spacer or washers on the sprag, so they are going to replace all of those with ball bearing units. He called this rollerizing the trans. They are also changing the planetaries, and adding a stage 2 B&M shift kit. So everything on the inside will be removed and replaced.

that was a great link, and a lot of useful info. gettin ready to rebuild my trans soon.