04Z06vette

what rear end ratio would you recommend for an LS1 and 4L60E for cruising and some long distance driving. I have a magnuson blower and we expect about 525HP. I presently have an open 3.08 10 bolt which I know will never hook up. Looking to swap to posi although this car will never be raced.

2nd question. should I go for a 12 bolt or 9 inch? again, not racing, but concerned that the extra HP might tear up stuff if tires ever hook up.

JoeNova

525 HP?

If its an 8.5" 10-bolt, a good set of axles and a strong Posi unit will be fine. 31 splines and an Eaton Tru-trac could last forever in that setup.

For gear ratio, Anywhere in between that 3.08 and a 3.73 is fine. It will depend on preference. 3.08 will keep highway RPM nice and low in overdrive. I run a 3.55 with a 28" tire and its great on the highway in overdrive.

04Z06vette

I think the stock setup is 8.2 inch with 25 spline axles and c-clips. I don't see as many options for that one. eaton posi and 28 spline axles and gears would probably be in the $1000 range.

JoeNova

You're right. The 8.5" didn't come around until 72 or so.

I would say a 9" is overkill for 525 HP. You should be able to find a 12-bolt on craigslist that bolts right in for a decent price.

67Skylark

GM made an 8.5 BOP 10 bolt back in those days that came factory with bolt in axels (no c-clip), factory posi with 373 gearing. My came out of a 72 Buick skylark but only had 273 gears. I'm running a 4L80 and had them replaced with 373, great cruiser. Happy hunting.

Isolde

iTrader: (4)

Go drive that 3.08:1 gently, get a baseline for what that cruises like, then see what you think of WOT in first gear. Hopefully you'll spin a tire rather than any a axle breakage. No sticky drag tires yet.
I had a Camaro with 350 / 700R4 / 3.08 / 26" tires, it worked well, same trans, axle, and tire in a 4.3L S-10, it got better mpg with 3.42s.
Note that the more gear you use, thd tighter your converter will seem. Loose converter plus deep gears is a guaranteed traction problem.