What's the difference between th400 and th350?

[Mrturner1]

I have a 1970 C10 long bed and the previous owner installed a Turbo 400 to 350 engine. Are there any big differences between the turbo 350 and Turbo 400? Is the 400 just stronger and rated for more horsepower? Or is there a difference in gearing and the way the shift wheels?

[Keith Seymore]

Yes - all of the above.

K

[Gmc.guy]

Th350 has a detent cable to the throttle on carb and T400 has an electric one to a switch on throttle petal in cab

[CG]

TH 400 eats up more of your horses

[Mrturner1]

Originally Posted by Keith Seymore

Yes - all of the above.

K

I'm kindof a rookie still to hot rodding and restoration. How is the gearing and shifting different? Is one more suited to a weekend driven go fast truck?

I'm starting to make sense of the PO's choices in parts that he put on this truck. He used it to tow a trailer to the track with a matching 1970 c10 on it, that one was a 10 second wheelie truck though.

I have some other projects that come before the tranny, but my long term plan is to buy a gear vendor overdrive, and no sense bolting that up to a tranny I don't want. I'll need to learn more but so far I don't think I'd bolt a gear vendor up to my current trans

[ryanv70c10]

Originally Posted by Mrturner1

I'm kindof a rookie still to hot rodding and restoration. How is the gearing and shifting different? Is one more suited to a weekend driven go fast truck?

I'm starting to make sense of the PO's choices in parts that he put on this truck. He used it to tow a trailer to the track with a matching 1970 c10 on it, that one was a 10 second wheelie truck though.

I have some other projects that come before the tranny, but my long term plan is to buy a gear vendor overdrive, and no sense bolting that up to a tranny I don't want. I'll need to learn more but so far I don't think I'd bolt a gear vendor up to my current trans

Gearing is virtually identical.


TH350
1st) 2.52
2nd) 1.52
3rd) 1.00

TH400
1st) 2.48
2nd) 1.48
3rd) 1.00

The TH400 is way beefier than a TH350. It was the trans that went behind big blocks and is virtually bullet proof unless your making big power.

[special-K]

Th50

[Mrturner1]

Originally Posted by special-K

Th50

What's that?

[Mrturner1]

Originally Posted by CG

TH 400 eats up more of your horses

This is interesting. I had a buddy with a 66 el Camino, 327/350 and I always remember the way that thing shifted. I'm definitely not a tranny expert, so I don't really know how much of a difference there is. How much hp do you think the 400 soaks up? If the 400 was behind the big blocks, is it possible it's more suited to towing than a truck built for 1/4 mile speed? I understand the difference isn't THAT extreme and it wouldn't be logical to say either trans could only do one thing well, I'm just wondering if my money is better spent rebuilding the 400 turbo I currently have, or if I should take the opportunity to switch to a 350 turbo

[TrkEnvy]

Turbo 400 is much beefier than the 350. If you already have a turbo 400 there isn't much use in changing to another non OD trans. Unless you are going to a OD trans the only thing you would give up with a 350 is some strength and some weight. IMHO the 400 is the better of the two and what I plan to run with a gear vendor. The way I see it is a 400 gives you room to grow. They also used the 400 in towing vehicles due to the fact that it was more stout and wouldn't get as hot as the 350 would have under the same load.

[69-72]

Originally Posted by Mrturner1

What's that?

It's the difference between the two

Th400 - Th350 = Th50

[CG]

You can google the horse power loss thing, but I seem to remember it takes about 35 more horses to run. Probably no big deal for a street driven truck, especially if you want the heavy duty-ness of the 400 for using your truck like a truck.

[hugger6933]

Matt, keep the 400. It is the heavier trans [in every way] but to change over to the TH350 is kinda crazy unless you HAVE to. You need a different driveshaft and the yoke is different too,look for headaches elsewhere. Just have your freshened up. That way it is a bolt back in and go and not have to worry about changing anything out.

[57taskforce]

Keep the th400... They are pure beef compared to the 350.

[stsalvage]

Most forget that there is one thing you can add to a th400 that will make you a very happy camper and it will hurt the pocket book for a little at 2500.00 But surly makes up for it in towing gas mileage and pure fun out and about Gear Vender turn that 3 speed into a 6 speed

[57larry]

I like the turbo 350. take it to a good tranny shop, they can build it tough

[The Chainsaw]

Th400 is a much better transmission than the Th350. That being said, there isn't anything wrong with a Th350 behind a cruiser.

The power loss is not going to be a set number. That all depends on how fast you are accelerating the parts. Slower acceleration is going to equal less power loss. I bet for a typical 300-400hp cruiser you would never be able to feel the power loss.

Space reasons would be the ONLY reason I would consider a Th350 over a Th400, but I would honestly just make room for it

[ryanv70c10]

Originally Posted by CG

You can google the horse power loss thing, but I seem to remember it takes about 35 more horses to run. Probably no big deal for a street driven truck, especially if you want the heavy duty-ness of the 400 for using your truck like a truck.

It's actually between 10 and 15 hp difference.

Powerglide is 18
Th350 is 35
Th400 is 48

These are rough numbers but pretty close to what I have heard over and over through the years.

[Mrturner1]

Originally Posted by ryanv70c10

It's actually between 10 and 15 hp difference.

Powerglide is 18
Th350 is 35
Th400 is 48

These are rough numbers but pretty close to what I have heard over and over through the years.

Wow, I never would have guessed that a transmission soaks up THAT much horsepower. What a bummer

[Ironangel]

If you already have the 400THM, thats the one you want. The 350THM weighs 15 lbs less and is geared slightly lower. The 400THM has more rotating mass than the 350THM which translates into a few extra pony's used to turn them. A properly built 350THM will indeed out run a 400THM for the same reasons a Powerglide will out run a 350THM. The bottom line is, in factory form the 400THM is designed to handle more torque and more HP than the 350THM is. Again, keep the 400THM because you already have it. I recently tooled up and learned how to rebuild 350 Turbo's because I have four of them, one in a 408 big block 72 C-10 drag truck, another in a 72 C-10 daily driver/ tow truck. So far I've only managed to break one and that was under no load in the tow truck with no trailer? And that was after 2 years and 10,000 miles of towing 9000 lbs all over the country...~Ghostrider~