Th400 built to hold 800hp

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Nov 9, 2009 | 05:17 PM

455GTO

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Th400 built to hold 800hp

I had the local trans shop precision transmission, overhaul my th400 to hold up to 800hp. It is a little over what I should be making on nitrous (750). Put in a tci RMVB and not sure what internals... Bill came out to $1058... Sound reasonable for that price? What parts in the th400 are a must to upgrade to hold up to 800hp? Thanks for any help

Also got an extreme warrior 3700 stall 10.5 inch converter custom built for my car by west coast converter.

455 block .30 over 463. forged rods and pistons cast steel crank. Hoping to spray a 200hp shot 10.5:1 compression

Nov 9, 2009 | 05:26 PM

rickou812

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Quote:

Originally Posted by 455GTO

You got screwed. You could have bought a complete trans for that.

The TH400 will easily handle that with very minor modifications. You should have spent at most $600 if you pulled and installed the tranny yourself.

Nov 9, 2009 | 05:29 PM

455GTO

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Quote:

Originally Posted by rickou812

I forgot to mention the trans front pump was damaged and metal went through the whole trans. Thats the reason for the rebuild and upgrade... Make a difference?

Nov 9, 2009 | 05:38 PM

rickou812

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Quote:

Originally Posted by 455GTO

I forgot to mention the trans front pump was damaged and metal went through the whole trans. Thats the reason for the rebuild and upgrade... Make a difference?

A little, but a front pump is +- $100. You can get a rebuildable core for about $125. So, I guess what I am trying to say is, for no more than $700 I can build a th400 with a transbrake that will handle >800hp. Once you start going over 1100hp, things start to get more expensive because you would have to start looking at after market shafts...

I am not trying to make you feel bad, and the price he charged you is pretty much standard fair these days at any commercial shop. They do have have quite a bit of mark up to cover overhead.

Nov 9, 2009 | 05:41 PM

455GTO

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Originally Posted by rickou812

Yeah I figured it was a little inflated. So what aftermarket internals are needed for the th400 to hold my power level? Thanks for the imput btw

Nov 9, 2009 | 05:49 PM

rickou812

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Originally Posted by 455GTO

Yeah I figured it was a little inflated. So what aftermarket internals are needed for the th400 to hold my power level? Thanks for the imput btw

Basically a good rebuild(replace all bushings, seals, paper, etc..), use high performance frictions in the direct drum, place a heavy duty snap ring in the case above the intermediates to add strength to the case lugs(which is one of very few areas that need strengthening in th400's), and depending on the year of your trans, you may have to update the direct drum and sprag to the heavy duty 34 element version and ensure proper front and rear end play.

There are a few other things, but that is the high points..

Nov 12, 2009 | 01:59 AM

455GTO

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I will be putting in a 2step for the launch. I was advised to have the 2step lower than my stall which is 3700. Reason being is because is gives a little slack on the launch about 6 inches then for it to flash to hit hard... I was thinking for the instant 3700rpm hit. Any advice on what rpm to have the 2 step at? I will also be spraying between a 200-250 shot operated by a wot and window switch. Thanks for any help.

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