7.5 rear from 4cyl

Gearbanger 101 said:

He'll be FINE as long as the tires spin!?! Dude, don't tell him that unless you're willing to foot the tow bill. The old 7.5" rear end was practically made of glass. It won't take much traction for him to compromise it. Certainly much less than a set of drag radials at a race track would provide.

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Back in '84, I bought a stock 5.0 5 spd Capri with 170 hp. It could spin the tires easily and I pounded the guts out of it and power shifted often and never broke the 7.5 it came with.

The physics behind my statement is if only 170 stock hp is enough to spin the tires, you could put 1000 hp in front of a 7.5 and not break it as long as you don't do anything to get more traction. Once the tires loose traction, it doesn't matter how much hp you have, the pressure is relieved from the rear. Big hp is only uselfull if you can get it to the ground and once you cross the threshold of traction, you are no longer putting stress on the drivetrain.

As long as he is traction limited, he won't break the 7.5 with 300+ hp because all the extra hp over what it takes to break the tires loose is not going to be stressing the drivetrain any more than the 170 hp my '84 came with from the factory.

Now take a car with a 7.5 and 300+ hp to the track with some slicks and turn all of that hp into useful hp by sending it all through the drivetrain with tires that stick... and something is gonna give.

On the street with normal traction street tires, he will never come close to breaking the 7.5 before the tires go up in smoke. And no, the 7.5 is NOT made of glass... there are many on here and other boards who will tell you they are running a 7.5 with big hp and it's still holding up. Yes, an 8.8 is good insurance, but the 7.5 isn't as weak as some may think.

I don't recommend that the OP goes beating on the 7.5 to find out if I'm right, but rather he asked if he could get by with it until he has the cash to upgrade... and my answer to him is yes, it will definitely hold up.

Just my opinion, but a 9" is overkill for 350 rwhp. An 8.8" is plenty sufficient, and cheaper, for that.