Should I keep the 9" or use a 10 bolt?

[68Malibu383]

I just bought an '81 Z28 that the prior owner put a lot of money into. ZZ4 crate motor, Art Carr 2004R trans, Moser 9"... I have the factory 10 bolt and am considering building that myself and selling the 9". By doing that, I'll end up with cash to put into other areas of the car and the 10 bolt weighs about 45 lbs less than the 9". The 9" has 3.89 gears so I'd need to at least change the gear set since that is too deep for the trans (TKO 600) and tire diameter.

I plan to use the car for autocross and open track and will eventually build an LS that should make around 525 HP. I will run street tires and don't plan to drag race the car on slicks so I think the 10 bolt will hold up fine. Before I sell the 9", I wanted to get opinions on this idea in case I am crazy!

[raustinss]

I'd keep the 9 myself ... better to er on the side of caution on the off chance you make more power or take it to the track

[andrewb70]

I'd keep the 9 myself ... better to er on the side of caution on the off chance you make more power or take it to the track

^^^This. I also wouldn't worry about changing gears in the 9" for now. Get it all together and see how you like it, then worry about what is "optimal."

Andrew

[BonzoHansen]

That zz4 won't break a decent 9" or 8.5".

It might depend if the 9" actually has decent parts in it. Not sure you can ascertain that at this point.

But if it ain't broke I'd leave it alone for now

[Frank ZX]

The 9 inch is strong but I've broke 2 back to back. This was a factory 3rd member. I haven't had any more issues since I put a nodular iron 3rd member.
I did run a couple 8.8 rears and they would strip the side gears.
This was all done on drag radials. A factory 9 inch will not hold more than 400hp if your putting power to the ground.
Something else I discovered, a 9 inch uses up more HP than a 8.8.
Here's a couple pics.
BTW, this is 4.6 Ford motor with a supercharger and 5 spees.

[Frank ZX]

It would spit the pinion out the front. I launched it hard enough that it bent my driveshaft, busted the input bearing retainer out of the transmission and cracked the block.
Atleast when I broke the 8.8s it didn't do damage like this.

[andrewb70]

For a 9" you need a minimum of a Nodular iron case and the Daytona pinion support.

Andrew

[Frank ZX]

For a 9" you need a minimum of a Nodular iron case and the Daytona pinion support.

Andrew

That's good advise.
Some people don't believe I could feel a difference in power between a 8.8 and a 9 inch. It could have been coincidence but my truck felt quicker with a 8.8.

[68Malibu383]

Thanks guys. The 9" is a Moser, so I would hope it has good parts, but I need to see if I can figure out what parts its comprised of. I know the current motor will not damage the 9", but I may sell that and put a moderate LS in there.

BTW, crazy damage, Frank!