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Stock TH400 HP limit?

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Post by Brainstain on Wed Jan 30, 2013 9:59 pm

I'm pulling the stock 350 out of my Vega an dropping in my cammed and carbed LS1. It has a 400 trans right now and I read on another random forum from a Google search that they can handle 450-500hp with just a stock rebuild. I should be right at 420-450 with the LS1 and I plan on using a 3200 rpm stall. Anyone know if it should hold?

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Post by Bruisr on Wed Jan 30, 2013 10:08 pm

They used 400s behind alot of big blocks in the 70's that had major amounts of torque. If any thing I would definately recommend putting in a stage 2 shift kit. Otherwise that thing wont even bat an eye. It will Handle it just fine!
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Post by Brainstain on Wed Jan 30, 2013 10:21 pm

That's kinda what I was thinking. Throw in a shift kit and a stall and roll out. The only thing I'm worried about is if I stomp it this engine is gonna come in hard at about 3500 rpm and jump to 7K pretty quick. Mostly, I dispise pulling trannies so I wanna do it right. Once.

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Post by 77mali on Wed Jan 30, 2013 10:27 pm

I think the TH400 was mated to Chev 375 hp 396's & Buick GS 455 when not equipped w/ the m21 & m22's (among others) from 68-72. IDK if they were changed any after 1972 though?

What kind of torque is estimated?
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Post by Brainstain on Wed Jan 30, 2013 10:34 pm

Probably a smidge higher than the HP. 450-475. The cam makes pretty level power ratings. It's a little cam but it makes good power. 230/224 .575/.563 111 lsa .

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Post by pila on Wed Jan 30, 2013 10:40 pm

My '76 Caddy Deville had one, and the listed torque for that engine (stock500) is 495 ft lbs. Low speed torque is maybe what to worry about. Haven't heard much about failures of the TH400.
I built a 400 for my Elco project, & used a Transgo shift kit. Engine is a 507 inch Caddy.
Hope you have a rear end that's as strong as the TH400 !! Very Happy

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Post by 77mali on Wed Jan 30, 2013 10:50 pm

I've been looking into 700r4 trans as a possible upgrade down the line. My new motor set up will be @ 350 horse but the torque is rated @ 415 ft lbs.

Long story short If i do this upgrade the shops that rebuild the cores do a few different mod's (stages) to handle that amount of torque & higher. The 400 is considered very beefy & like Pila said I've never heard of one failing that was well maintained. I just like the idea of the overdrive to save on fuel but I will have to change the rear end ratio too...3.42-3.73 seems to be what most guys are upgrading to w/ the 700r4 swap.

I've posted this link a few times but you may want to call and pick their brains. They seem to be a well respected company & get mentioned quite a bit in other forums.

http://www.transmissioncenter.org/contact_page.htm
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Post by Bruisr on Wed Jan 30, 2013 10:54 pm

Before you commit to the 700r4, look into the 2004r they claim to handle more power and require a little lees to install. You wont have to change the yoke on the driveshaft, relocate the crossmember or better yet you wont have to shroten the driveshaft.
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Post by Bruisr on Wed Jan 30, 2013 10:56 pm

I retract my statement on relocating the crossmember, I just remebered you will. But I've heard lots of people say the 200 4r is a much better tranny, and needs less modifications internally.
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Post by 77mali on Wed Jan 30, 2013 10:59 pm

Bruisr wrote:Before you commit to the 700r4, look into the 2004r they claim to handle more power and require a little lees to install. You wont have to change the yoke on the driveshaft, relocate the crossmember or better yet you wont have to shroten the driveshaft.

Will do. TY
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Post by Bruisr on Wed Jan 30, 2013 11:08 pm

Do you remember the Buick Turbo Regal? The 200 4r was the tranny behind that rocket? And that was factory stock!
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Post by Brainstain on Wed Jan 30, 2013 11:13 pm

pila wrote:My '76 Caddy Deville had one, and the listed torque for that engine (stock500) is 495 ft lbs. Low speed torque is maybe what to worry about. Haven't heard much about failures of the TH400.
I built a 400 for my Elco project, & used a Transgo shift kit. Engine is a 507 inch Caddy.
Hope you have a rear end that's as strong as the TH400 !! Very Happy

It has a narrowed 9" with a full spool and 3.73s and 295/55/15s. The gear needs to come up to a 3.42 though. Too much gear for a car that light.

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Post by Brainstain on Wed Jan 30, 2013 11:15 pm

Ha! I blew out the 200R4 in my 89 Caprice. I upgraded to a 700R4 ad it was much better.

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Post by 77mali on Wed Jan 30, 2013 11:54 pm

Have you seen the 700r4 "Raptors"? Pretty sick.
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Post by BlackChevelleSS on Wed Jan 30, 2013 11:59 pm

Getting in a little late but th400 is a great strong trans. If your going to be using it without rebuilding, I STRONGLY recommend installing a stronger intermediate snap ring. All you need to install it is a pump gasket and seal. If you are rebuilding it, I still recommend the snap ring, upgraded sprag, and tail shaft torrington bearing mod, koleen steels and alto red clutches
ALSO th400 SHOULD NEVER SHIFT HARD TO SECOND! If you install a shift kit that makes a hard second shift, you will be looking for a new trans soon.

I rebuilt my trans myself with all of these, 9" 3000 stall convertor, and transgo shift kit. My car is 4000-4200lbs, 3.31 gears 28" tire, and pushing 500-550hp 600tq. I have probably close to 200 trips down the track and about 5 years of abuse. 15k miles on it.

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Post by 77mali on Thu Jan 31, 2013 12:06 am

How do you know which converter will work best? How is that calculated?

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Post by BlackChevelleSS on Thu Jan 31, 2013 2:07 am

By camshaft and head selection.

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Post by pila on Thu Jan 31, 2013 7:56 pm

There's an outfit that builds the 2004R to handle big power, and of course they are like 3600 bucks.
That 9 inch will handle your power fine. I'm using one also, a Currie.

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Post by Brainstain on Thu Jan 31, 2013 8:42 pm

If the 9" breaks I'll step up to 35 spline Moser shafts.

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Post by 2fat2fly on Sun Feb 03, 2013 6:37 pm

Brainstain wrote:I'm pulling the stock 350 out of my Vega an dropping in my cammed and carbed LS1. It has a 400 trans right now and I read on another random forum from a Google search that they can handle 450-500hp with just a stock rebuild. I should be right at 420-450 with the LS1 and I plan on using a 3200 rpm stall. Anyone know if it should hold?
here's a thought ! 477 cu. in., 13-1 motor, 4.56 gears, 5250 stall, 750-800 hp, low 10 second 1/4's, 400 with 34-36 roller sprag, good set of alto disk, shift kit, very few mods, runs hard all day, carries the front end out of the hole.
I'm on the same page about that small block not being able to harm a good 400 with a few mods, just a thought !!
[img]Stock TH400 HP limit? 38166814[/img][img]Stock TH400 HP limit? 38166815[/img]
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Post by pila on Sun Feb 03, 2013 8:54 pm

I don't think you can break a mildly built 400 with a small block, no matter what the dyno says....

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