hey guys...

Im just wondering what you guys think i will run.....my car is an 83 z28 with a 355...the compression ratio is about 9.5:1, it has a comp 280h cam, edelbrock performer rpm intake manifold, ported decked and polished 194 heads with 1.52 roller tip rockers, a edelbrock 600 vs carb, msd distrubutor, hooker headers, flowmaster exhaust. The tranny is a turbo 350 with a stage 2 trans go shift kit and a 2800 stall converter.... a 8.5" rear end with 3:23's.....
The track is at sea level btw...thanks in advance

 

You have a 7.5" rear end not a 8.5"

 

oh ok.....i was told it was an 8.5" by the guy who sold me it....is there anyway to tell without take the cover off?

 

8.5's never came in a 3rd gen. If you do have an 8.5 it would be custom and most likely need ladder bars or SSM kit to make it work.My guess for an et would be low 14's maybe a hi 13

 

my friend has almost the same combo with less camshaft ,he runs 14.2s on street tires.

 

Look at the rear cover. If it's smooth and has 10 bolts holding it on, you have a 7-1/2" 10 bolt. If there are 9 bolts on the cover and there's a rubber fill plug on the back, you have a BW 9 bolt with 7-3/4" gears. If there are 10 bolts holding the cover on and there's a metal fill plug in the cover, you have a very rare, 8.5" Dana 44.

The majority of all third gens have the 7-1/2" ring gear. Somewhere around 1986, GM switched to 7-5/8" ring gear. It's the same, just slightly larger and normally still referred to as a 7.5".

Only a diff from a third gen will fit into a third gen unless you have an aftermarket bolt in 12 bolt or ford 9". A second gen 8.5" diff won't fit because the third gen needs a torque arm mount to work if it still uses the factory style rear suspension.

 

If those are stock heads, low 14's or high 13's.