What sort of horsepower can a 83/4 diff carry. JUst checking if it can handle about 340hp or would I be better off with a 9 inch.

 

What are you planning on doing with the car? Street car? Weekend warrior at the strip? Slicks?

 

Street car, with the very odd trip down the strip, to blow out the cobwebs.

 

Assuming it's a small block (hard to stuff a BB in a '66), you'd probably be just fine with a 4-pinion differential in an 8". Assuming that's what you have in there, that's the cheaper/easier way to go.

The 8.8 out of a fox body would take more abuse than an 8" and is lighter than a 9", but unless you don't have a proper-width 8" to work with, it's more effort than it's worth.