Thoughts on rear diff upgrade

[CamaroCracka]

Originally Posted by LS3_JC

Man please show me where you can find a ZL1 diff for cheaper than$2500 I’d have luck finding one for that price.

That was 2018 and you could find them all over for under $2500. I sold a 3.23 for $1300 and that took a while. Now they have gotten rare and people are paying over 3k, which, after axles and drive shaft, puts them near enough to a 9" price point that it really makes a 9" setup look attractive. Support for the 9" is far superior to the ZL1 diff and even the S60 has better options and parts availability than the ZL1.

[Eastbaycamaro]

If you are not drag racing I think you will be fine with 3.91 and the stock posi unit. I broke the spider gears on my stock posi unit after a lot of abuse on the street and the 1/4 track. Also my car would wheel hop quite a bit. I then upgraded to a tru trac with 4:10 motive and ended up breaking 8 teeth off the ring gear. Since then upgraded to a strange s60. Also I rebuilt my stock posi unit and had the new side gears and spider gears cryogenically treated but haven’t got a chance to try it out.

[acammer]

Originally Posted by acammer

Limited gear options keep me away from the ZL1 diff. If I ever upgrade beyond building up the SS rear it'll probably be to an S60. Unless I add a lot more power I should be ok with the well built SS rear.

This aged well, lol. Since 2018 I have broken the factory 218mm rear end several more times. I finally did what I should have done in the first place, and got myself a 9" G-Force IRS setup.

In the last five years I've done a very deep dive into all things driveline on these cars, specifically within the context of drag racing a manual transmission combination. What I've come to determine is that the stock SS rear end is just not going to cut it for any serious, regular drag racer, with a manual car. The case is soft (aluminum), the ring gear is small (limits tooth size), the car is heavy, and powerful, and that combination just lends itself to breakage under anything less than ideal conditions where the diff is never shocked and is always loaded smoothly. Unfortunately, modern IRS cars like ours have many more points of lash in the driveline, and all of that contributes to increased shock loads and potential for wheel-hop.

The problem gets amplified as you make changes to the car to add power, or improve the gear ratio. Consider when you go to a 4.10 gear ratio, which is the best option available for the rear end for a manual car, from a performance perspective. The ring gear stays the same size, which means the pinion decreases in size by 18% to achieve the 4.10 ratio. So, now you've got smaller teeth, and are producing more torque. That torque is more likely to introduce deflection in that soft aluminum case - and with any case deflection and the gear engagement is less than perfect with weaker teeth then it will eat itself pretty quickly.

The ZL1 rear end used to be a much better go to option, as they were plentifully available, both used and new from GM. The GM option is no more, and the used options have dried up substantially, especially in the 3.73 ratio, which is far more desirable than the 3.23. The other problem with the ZL1 is that you're limited to those two ratios. For many serious drag oriented builds, that's not enough ratio. If you've got enough power, you can make that work, but naturally aspirated builds need all the starting line ratio they can get, and lots of RPM out the back.

That leaves the S60 and 9" - man, those suckers are expensive. Ultimately, I wish I could have made the logic jump to the 9" years ago, because I spent a big chunk of money rebuilding those stock housing setups before I finally made the change. Now I've got a fairly bulletproof setup, and the perfect ratio for my build. So, for those thinking seriously about rear end upgrades, I would encourage you to really look at what you want to do with the car. If it's sticky tires and hard launches, then the stock rear end will be a continual disappointment, and money suck. Buy once, cry once - it rings true for this conversation.

[CamaroCracka]

Is the drive shaft GForce too?

Like those cutouts in front of the garbage cans. Do you ever even cap them?

[acammer]

Originally Posted by CamaroCracka

Is the drive shaft GForce too?

Like those cutouts in front of the garbage cans. Do you ever even cap them?

Yes, it's a 3.5 inch aluminum driveshaft by g-force. They actually don't make them anymore, apparently they have more than enough work making the rest of the components and there are other drive shaft companies out there that they will recommend.

I ran that exhaust setup for quite a long time. No, I rarely would put the covers on them to close them, with them so far in the back it truly wasn't super awful inside the car, with most of the noise being behind you. Here's a picture of the new setup, which I went to strictly for the weight reduction. This saved about 65 lb. The downside is it's much louder inside the car, and obviously there's nothing to cap on a long trip to make it nice and quiet. The things we do for fractions of a second.

[Sales@Phastek]

The 3.91 would be you best choice.