Hey guys,
Im in the process of tackling the rear end for a future AI camaro. I've seen different set ups for different applications.
I currently have 85 Iroc with 7 5/8 stock 3.73, with Power Traxx posi. I carry ZR1 11" on back with spacers. Id like to beef up rear, add disc brakes and set up proportioning valve. Which option would be best for least money. Chattanooga, TN.

have you done a search on this topic??

The diff you have if fine. Keep it. Best bang for the buck.

If I was moving form CMC to AI, I would run the very same diff I have now, a stock 4th gen 10 bolt.

Ford 9". Any stock rearend, even freshened, is on borrowed time at AI power levels in my opinion.

I disagree. You bought 2nd hand rear ends that probably had garbage set-ups with aftermarket gears, and didn't you have a clutch issue at the time?

Randy M. was putting 500 HP through a 10 bolt with a 3.91, I think a GM 3.42 / 3.73 with a good set up can last a long time with <350 HP. Maybe not forever, but a long time.

I was putting approximately 460 to the rear wheels with the "stock" rear. At that level, it would break once a year like clockwork. Of course I was using 3:90 gears...which, I believe are thinner cut like a 4:10, and 9 times out of 10 only the ring and pinion was bad. I lost one T2R in 6 years as well.

Most of them were stock 3.42 rear ends, one was a 3.73 but that one had the pinion nut back off. The clutch issue was just a Quartermaster clutch, they're harder on driveline parts on take off and until you get used to them, more likely to wheel hop on downshifts.

We had a CMCer break a 9-bolt earlier in the year. Power levels are not the biggest contributor to gear breakage, IMO. Wheel hop under braking is the biggest issue, followed by rough treatment over curbs, and shock loads from breaking the tires loose and hooking up. Wheel hop will break shit, I broke the pinion support out of 9" center earlier this year from standing starts running a setup with negative antisquat.

The other thing to think about is amount of use. A 10-bolt will last a lot longer time wise if you only run 2-3 events each year and call it a season. Running a 7-8 event race season puts a lot more abuse on it then track days.

My vote, 4th gen 10 bolt. You could probably find a V6 3.42 with an open diff and disk brakes for dirt cheap. Do some searches on the best diff to use, buy it, swap it in. Look over the axle shafts in the wheel bearing area for spalling, that is common. Depending on trans, engine torque curve, and the tracks you run at you might like a 3.73 gear better. If you're changing gears I'd recommend new bearings at the same time and you'll need to do a whole new set-up which can be time consuming to do right.

I'm still on the same axle for 6 years(10 events per) of tracking and racing. It has been rebuilt 3yrs ago when I put stock style 3.73 in. It has a 6yr old T2r in it with good axles and setup. I know it's on borrowed time at this point, so I have pretty much the same axle ready to swap in at the track if needed.

You could run it till it goes Bang, than spend the bucks for what you want.

If you are the kind of guy that does his own work then you can get by just fine with a 10 bolt. Suppress wheelhop as best you can and make sure its set up right. If you drive over curbs and thru the dirt and grass like me than you should be breathing the throttle to go easy on the parts.

On the other hand a 9" can offer more flexibility and options with parts, quickchange capability and of course stronger. More weight and up front cost though.

Another major issue that needs to be considered is your geographic location. Those of us who experience extreme climate changes, including deep freeze cycles are more likely to be driving / racing on bumpy tracks. The freeze / thaw cycle really does a number on asphalt. Bumps under heavy load tear up weaker rear ends, regardless of the hp levels.