Im looking to buy a new rear for my car and was wondering if the extra strength of a 9" is needed for my application? Ill be running a 520 hp 383 thru a T-56 tranny and 4.10 gears. I was going to get a Strange 12 bolt, but was wondering if trips to the drag strip (5 or 6 times a year?) and clutch dumps would break the 12 bolt at my power level? I like the fact that the 12 bolt is lighter and takes less power to spin than the 9". So would I be better off getting a 9", or would a 12 bolt be fine? Thanks.

 

IMO a 12-bolt should take care of you just fine. They survive behind big blocks; so some little motor like a 383 shouldn't be an issue.

The 12-bolt fits the car quite a bit better, in a general sort of way.

Also IMO, the main advantage of a 9" is not just raw strength, but rather, the ease of changing gear ratios. If that's not something you're going to be doing on a regular basis, then the 12-bolt is a better choice.

 

^^^^^^^^^^^
Yep. - There are plenty of guys running 700+hp on 12-bolts. Super stock cars are dropping their 9" in favor of a 12-bolt since it's lighter internals take less power to pull, and the technology is there to build them strong enough.

 

Well thats good to know. I was planning on getting a aluminum cover for my 12 bolt as well. So Ill have the cap support. Thanks!

 

i know this is an old post,but just to let you guys know.strange engineering has a "drop out" 12 bolt center section.it's 9 lb lighter than the lightest 9in center section and it will bolt up to the 9 in housings.i'm debating on going this route when i get the 9 in housing from moser.only thing is it is a little pricey.they run about 1200 to 1300 just for the center scetion already setup

 

the factory 12 bolt vs. aftermarket unit is also night and day difference. aftermarket 12 bolt vs. market 9 inch the real advantage would be the gear changing as sofa has said.

 

Well lets say I get a Strange 12 bolt and will be getting an Eaton Posi and 3.73's...but I wont be changing gears after these are installed.....so would this be fine for me also?

 

I like my 9" for a couple of reasons but mine is also a full race diff and never sees street use.

Parts are plentiful and cheap for a 9" because it's used by so many. Yes a gear swap can be easy with a 9" but what most people thing of is chaging the entire third member. That means having a second case, carrier, pinion retainer, toke etc to make it a simple quick swap. Even then, a quick swap would be 1 - 1-1/2 hours depending on location and tools.

I just did a gear swap in my 9" last week. Kept everything else and just swapped the gears. It took me at least an hour just getting the gear pattern that I wanted. Including the time it took me to jack up the car and pull the axles and third member, the entire swap took about 3 hours. Of course when the shims are behind the bearing retainer and not behind the pinion bearing like in a 12 bolt, setting up the gears is a lot easier. Pull the retainer out, change the shims and bolt the retainer back in. I also use a solid crush sleeve so setting the pinion preload is easy.

Swapping gears in a 9" is also easier since you only need one carrier. Doesn't matter if you have 2.50 gears or 6.00 gears, they all fit the same carrier. A 12 bolt has a different series carrier depending on the gear ratio. Although you can buy different gear thicknesses to use on different carriers, you may not find the exact ratio you're looking for or you may find a ratio in factory gears that needs the different carrier.

The power consumption isn't great enough for a typical street engine to notice a big difference. The 12 bolt uses a 8-7/8" ring gear so it's almost as big as the 9". The pinion location sits in a different location though so that's why it needs the different series carriers.

A 12 bolt uses 30 spline tapered axles and there's a 33 spline aftermarket. The 9" has factory 28 and 31 splines with upgrades to 33, 35 or even 40 spline axles for those 2000+ hp engines.

A 9" can be made a lot lighter by using an aluminum third member and pinion support. At least 20 pounds can be removed by using the aluminum parts. For drag racing, a spool is recommended. Although a steel spool isn't very heavy, an aluminum one is also available to take off even more weight. It's all unsprung weight. Get into even more weight saving by using a sheet metal housing.

For a typical street car with the occasional track time, a 9" or 12 bolt will work fine. You're not going to hurt either one and you won't notice a performance difference from using either one. Buy what you like or prefer.