ok guys, i have a 82 z28 pace car.. it had the 305 4bbl.. it has the stock rear end.. later on down the road i want to put 600hp big block, but for now to get it driving and starting to enjoy the car i am putting in a 383.. i have not built it yet but it got me to thinking.. how much HP with the stock rear end hold? i plan on doing the 9" rear end later with the Big block.. but for now i just want to get the car mobile and start to enjoy it.
thanks
Roy

 

Stock diffs have been broken on the street and beefed up one have survived 10-11 second 1/4 mile passes. How much power it can take depends on a lot of factors so there's no exact answer. You're going to roll the dice every time you abuse it on the hopes that it will survive.

You can spend money trying to beef it up but no matter what you do, you can't change the fact that it still has a tiny ring and pinion with tiny teeth. Start saving your money and spend it once an a 9" or 12 bolt before the engine is capable of breaking the diff.

 

Stock versions are a roll of the dice, as noted by Alky. I've killed 3 stock axles with 305s, and I've had a 26-spline 7.5 with welded diff survive a summer of 10.2-second passes down the 1/4-mile, behind a seriously built 355 / 700R-4 combo, in a full-weight '88 IROC-Z. I used drag radials at the track, but not on the street. However, the 3 I broke, all 3 were on street radials, of a 235-width, same as my IROC ran on the street. If you don't have the money for a 9" or 12-bolt, then get a spare 7.5 for reference and brackets, and get a Ford 8.8" from a Lincoln Town Car, and get to work prepping that 8.8 for your Z. The 8.8 can be built just as strong as a 12-bolt, at much less cost. While scrounging the 8.8, decent gearing and 31-spline axles can be found in F150s, along with worn-but-rebuildable Traction-Lock diffs. Likewise check later Explorers, for the gears, diffs, axles and the best disc brakes. I'm not really clear on the various lengths of the axle shafts, but something will be close enough. It is possible to leave the yard with all the good stuff for under $200.

 

could you point me in the right direction to find out which length axles will work. this is something i am VERY interested in.
thanks

 

The Town car is supposed to be the closest match on overall width, but it never got 31-spline shafts. I'm working on the same plan as others have had success with, and here's my step-by-step plans: 1: arrive at yard, pay admission, put toolbox in wheelbarrow. 2: wander around looking for Town Car with 8.8 axle. 3: pull it, load in wheelbarrow, longways. 4: Wander over to pickup / SUV area, looking for F150s and later Explorers. Check each for 3.55:1 gears, 31-splines, and Traction-Locks. I may score the gears in one vehicle, the T-L in another, the shafts in a third, and the brakes on a fourth. But The Town Car's 28-spline 2.73:1 open diff can be left laying in the gravel, with the good truck parts stuffed in the car housing ( Which is also lighter ) I may have to try both the F150 axleshafts and the Explorer axleshafts, dunno, but not worried. May happen to need a pair of left shafts from an Explorer, or may happen to need a couple of right shafts from an F150. Whatever, something will be close enough, and it's not like there aren't dozens of them in the yard on any given day.

 

Hello you are talking about the 8.8 I'm very interested about it. Can I ask you some questions about it I know I have to weld the brackets on but will I have to cut it or is it the same length and will I have to run a special bracket for the torque arm it will be for a 1985firebird 350 small block and thank you

 

think i am going to try this.. this coming weekend the pick n pull yard is half price.. i have never done this before with rear ends but i am going to give it a try.
any pointers?