How long could I expect it to hold up behind a 600 fhp big block? No slicks at first until I get a decent rear end under it? I want a 4spd big block car but I am thinking a nice TH400 would be the way to go for serious thrashing. Your thoughts?

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Bill
65 SS
Team Member 1013

well without slicks you should be fine mine is only425hp,with an M20 and it's taken a LOT of abuse along with daily driving for the last year (and i bought it used) the tires help cuz they just break loose http://www.chevelles.com/forum/smile.gif with slicks that's when you start breaking stuff. but ask DZ he seems to be the expert on em

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1970 SS396 AKA 454/4spd
My Chev-Hell Page (http://hometown.aol.com/jnkb2cool/home.html)
Member #783
Ft.Worth, Tx
Big Block Chevy.net (http://www.bigblockchevy.net)
proud owner of this site
(oo|ss|oo)

I've been powershifting my M20 with a built 427 in front of it for 10 years now... http://www.chevelles.com/forum/biggrin.gif
It's never complained once.

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1970 Chevelle SS396/M21/4.10 My 70 SS396 (http://www.chevelles.com/showroom/mr4speed70SS1)
Engine pic (http://chevelles.com/showroom/mr4speed70SSengine2)
1970 Chevelle SS454My 70 SS454 (http://chevelles.com/showroom/mr4speed70ss454)
1968 Oldsmobile Cutlass convertible
1982 Oldsmobile Cutlass 350 Olds,TH350(daily driver)
Chris Corwel,TC Member 785

I have asked this question many times, and never got a concrete answer to it. DZAUTO finally put things in perspective for me.
When these transmissions were engineered, you could not buy 600 hp from the factory. They are designed around 400 hp. The way I figure it, most things are engineered to withstand more than they have to as an engineering comfort factor. At probably 10 to 15 percent more, you are still only looking at around 460 hp. Now, I don't know the exact over engineering benchmark, I am just using this as an example. The point is, you are pushing the limit of that transmission. However, if it doesn't break, then it's good, right?
I am running around 525 hp and I broke the tranny once. However, I do not think the HP is what broke it. I believe I had a cracked countershaft gear tooth. After the rebuild, I have done numerous launches with some BFG drag radials. Got these to hook up well enough to keep the black strips on the pavement down to about 15 feet or so. This is under full throttle from a dead stop without "dropping" the clutch. Should hook up better at the drag strip. Tranny is still ok.
Hope this helped some.

Dave


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69 Chevelle
454 .030 10.5:1
373 posi
M21 4spd.
Nothin But Fun

"Fire all your guns at once and
Explode into space."
Steppenwolf "Born to be Wild"

As long as you run street tires you should not have a problem. The addition of slicks, traction devices and the weight of a Chevelle will lead to the early demise of the trans. They can stand a lot of abuse but if you get the heavy barge hooked to the ground and you are making serious HP, it's only a matter of time.