Safe maximum HP and Torque for Drivetrain

[1971gophercatcher]

My project is a 1971 C-10 Cheyenne Super

I need some expert guidance here. My goal is to upgrade to a new engine and keep my stock TH 350 transmission and stock 3.07 non Posi 12 bolt rearend.

What is the safe maximum amount of Horserpower and torque that my stock drivetrain can handle? I would like to stay between 300 and 400 for HP and torque if I can.

Please share where I can find this kind of information. I’ve been all over this forum and internet with no luck.

Thanks in advance!

[weq92f]

.
Flip fa ya...

[72 k15]

The 12 bolt should hold good, Im thinking you will be fine with the turbo 350 at 300-400 hp/tq Long as you dont get to hard on it.

[Greasey Harley]

How high is up?

That is to say, it depends on how you drive.
If you launch the thing hard, parts will break. You could break perfectly good drive train parts with a 225hp V8, just by driving like an idiot (like me).
If you drive reasonably, 400+hp should be no problem, if everything is in good condition.
...or this (This one wasn't me)

[weim55]

While I can't give you an outside source I can give you one with lots of experience. Both the 12 bolt and TH350 Will handle that power output no problem if they are in good condition to begin with.

Steve weim55 Colorado

[jocko]

All comes down to driving habits. Unless you do neutral drops at every light, you'll probably be fine... Least expensive approach is to drive like you stole it til something breaks, and then you'll know what the weak link is.

[WorkinLonghorn]

I would say that the big block trucks came with the TH-400 for a good reason. Unless you have the TH-350 upgraded I would not feel good with more than 350 Ft/Lbs. Also, what the guys said above of course about abusing it.

[Overdriven]

A few years back I picked up a th350 for a project and went to have it rebuilt locally. Since the trans was in the back of my pickup they started asking questions. Realizing this was my weekend toy/stress reliever and 350hp goal they recommended some upgraded clutches and such, and some valvebody tweaks to go along with the basic rebuild. I think it added less than $50 to the bill for the upgrades. Far from a “built” trans, but just enough upgrades and tweaks to handle the extra power and abuse of being a weekend toy/stress reliever.

I’ve seen enough anecdotal evidence on this site to suggest your rear axle will be fine. Unless there’s something wrong with it and/ or you’re going to bolt on slicks and take it to the dragstrip every weekend.

[kwmech]

A quality built T350 with a good shift kit will handle 3-400 hp without any problem.

[davepl]

The TH350 can be built trivially to take any amount of power up to about 600hp, and even much more but it gets pricey. But 300-400 is nothing.

In stock form you'd want (and prefer) the TH400. But any good performance trans shop can make the TH350 live.

[hjewell2]

Originally Posted by davepl

The TH350 can be built trivially to take any amount of power up to about 600hp, and even much more but it gets pricey. But 300-400 is nothing.

In stock form you'd want (and prefer) the TH400. But any good performance trans shop can make the TH350 live.

Darn tootin, running a real hot SBC 500 HP 4200 converter TH350
4:10 gears 8 7/8 eaton 12 bolt I never show it any mercy track or street
5yrs and going.
;

[HO455]

3.07 open rear with small tires you will be fine. Your real concern should be a rev limiter. Our 64 GTO race car puts 440 lbft of torque down on a chassis dyno with a T350 and a 12 bolt. Small tires keep it in one piece.

[jamyers]

I've got a TH350 with over 100K miles behind a 510 ft-lbs 464cid Buick in my '71 LeSabre, it's fine.

That said, it's the heavy duty version of a TH350, called a TH350B iirc, has extra clutches in one set and has a mild shift kit. 4300lb car with 3.08 posi and 28" tires. I don't abuse it, but I don't baby it either. (if/when it dies I've got a Switch-Pitch TH400 standing by)