I'd like to stick a big block in the "velle as it currently has a 350/TH350 combo. However my goal is not to gredade the transmission if I decided to throw a set of sticky Mickeys on the old 12 bolt and run at the track.

With that being said how much would this old TH350 handle?

My son has been running a turbo 350 behind a 540 cu. in. Big Block in a Chevelle that has somewhere in the neighborhood of 775-800 H.P. and has even sprayed it some although i wouldn't recommened it. The car usually runs high nines and the only problem he has had is one broken sprague. This trans was beefed up by ATI and has a real good converter also by ATI. Best E.T. is 9.42 and the best speed is 147.61 MPH on a little juice.

I was thinking of running it as is for the time being but didn't wanna beef it up unless absolutely necessary.

A shift kit,good converter,deep pan and external cooler and you're good to go, providing the internals are in pretty good shape to begin with.

How will a shift kit,good converter,deep pan and external cooler keep the tranny from grenading by the brutal power of a big block? :confused:

Only things I see that come from that are tire chirping shifts, higher rpm launches and cooler fluid.

Oh, I will be using all of the above as well. ;)

the th350 are pretty tough trannys i have a stock rebuilt one behind my bbc that runs 10's and it has just a shift kit installed nothing is "beefed up" its just a good rebuild......the convertor is a tci unit and as well i have a cooler..................in my 80 z28 i have a bbc too in front of that stock th350 tranny and that bbc is making 356 hp to the rear wheels it too has a shift kit ,tranny cooler and a advertised 2800 stall ..............

it has been in my experiance that the th350 will last behind alot of hp......but if you start treating the tranny wrong they wont last even behind a stock engine.......liking throwing it down into first gear just to hear your engine roar........stalling your convertor alot sitting up against your brake......not keeping them cool..(good tranny cooler needed) tranny drops and rolling back putting tranny into drive.....

Any spinning, like on a burnout, then hooking, with your foot still in the gas will result in the sprague saying goodbye. You MUST get your foot off the gas if the tires are freewheeling or the sprague will break when in hooks on either a 350 or 400 Turbo. As long as you get "out of the gas" before it "chrips" and you'll be O.K.. I agree with Rapid Robert and ddeennis about the shift kit, better clutches and tranny cooler as these items are a must for any Turbo you are planning to beat on.

P.S. My son trashed three different transmissions before he changed his method of doing a burnout. Start in low, shift into second and follow that by getting into high to get the tire speed up keeping the RPM at about 3000-4000 and then get out of the gas when you feel the car starting to bite. After the burnout go straight to the line (no dry hops).A friend of my sons was burning the tires on his truck around a corner with street tires and suddenly got traction. His childish display put him afoot quickly. (broken turbo sprague).

Running mid-low 11's with a fairly stock TH350 with lots of hard street miles behind my 383 for a couple years now. It has nothiong more than a good pump, shift kit, and a good clutch pack. My engine may be a small block, but being a stroker it makes lots of TQ -- probably similar to a mild BBC.

ps. times in my sig are old -- new best is 11.31 @ 121.8

Ddeennis: liking throwing it down into first gear just to hear your engine roar


What do you mean by that? Like being in second at a cruise and shifting into first when you mash the pedal?

My kickdown does that anyway?

Pretty much been covered here.

Weaknesses inherent to a stock TH350 are the intermediate sprag, direct clutch apply area, sun gear and direct drum bushings... Really about all I can think of.

A shift kit does several things to improve the trans.
Most importantly, almost all of them dual feed the direct drum piston to increase apply area to 3rd gear. You MUST have this for the directs to live under HP. You can do it via a shift kit, or by internal mods, but it needs to be done.

They also firm up the shifts, this limits the amount of slipping going on when a shift occurs. Less slip=less heat.

That said,
heat is a killer to an auto trans. The friction clutches are made of a paper matrix, that is bonded to the metal and itself by a resin.

The heat kills the paper and the resin...
So this is why you need a good cooler, extra capacity pan, etc..

Next,
The intemediate sprag is a weak link in both the Th350 and 400 as stated. Doing a burnout wrong is common cuase for racers to break them, too hard of a 2nd gear shift it how most street guys break them.
I recommend TransGo shift kits because they will prevent failure of the sprag. TCI kits are similar. I personally as well as all other professional builders I know avoid B&M kits, but some have had OK luck.

Th-350 in my car, Built by Steve Gillian's Transmission Repair

Any spinning, like on a burnout, then hooking, with your foot still in the gas will result in the sprague saying goodbye. You MUST get your foot off the gas if the tires are freewheeling or the sprague will break when in hooks on either a 350 or 400 Turbo. Does this even apply for a beefed up tranny?

I've done similar to one of my other TH350s....I would have the line lock set, trans in first, roast them, then let off the line lock, then shift to 2nd to keep the engine in it's power band and (on the road I was on) would let it spin for a little bit in 2nd before it finally gripped and stopped spinning. This was of course just having fun on a country road, and not at the track.

However if this so-called method I'm doing is bad I'll stop now....not really wanting to blow apart a tranny.

Yes, it makes no difference whether you are just goofing, or at the strip, ANY freewheeling then hooking will kill the sprague in short order, if it is spinning get off the gas before it bites. You might get lucky a few times but not for long. my sons would just lock up like it was stuck in two gears at the same time.

Originally posted by Twilightoptics:
Ddeennis: liking throwing it down into first gear just to hear your engine roar


What do you mean by that? Like being in second at a cruise and shifting into first when you mash the pedal?

My kickdown does that anyway? running down the road and pulling it down into first to say just to hear your exhaust roar.....or shuting off the engine at high rpm to check plugs for a/f readings shouldnt be done either.....