In a previous insert i was told that i am twisting input shafts on the 904s in two because i am running the older smaller torque convertor.
Why is this, what is the science or mechanics behind it??

I think whoever told you that is full of it. I've never seen a twisted input shaft. However, a common failure w/ higher HP engines is that the pump drive hub on the converter can split or break off. That might be what they meant?

Lou

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Home of Slant6-powered fun machines since 1988

The 60-67 904 (small hub) uses a smaller, 3/4 diameter input shaft w/ course splines.
The 68 & later 904/998/999 (big hub) transmissions use a 7/8 diameter shaft w/ fine splines.
You must have a pretty powerful SL6 to be breaking the input shaft off the trans.
DD

ya about 300 horse maybe if i am lucky quarters in the 11's when i get lucky usually 12-13's but i twist my input shafts in two or i will blow or suck the the front pump seals out in the tranny

Sounds to me like you need to have someone build your trans that knows what he is doing. Broken input is a sign of internal issues, not horsepower.

Do you have tire screeching, neck snapping shifts?

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Official Cookie and Mater Tormentor.

Where are you located? It might be nice for some of us to meet you and see your fast Slant 6. Or, you could come to a Slant 6 drag race?

Lou

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Home of Slant6-powered fun machines since 1988