about a year ago i put a 12 bolt in my car. so far its great but i was wondering how much stronger a 9" is?? every time i look at a car on the board that is making some serious power it has a 9". a little late now, right haha . but i still want to know how much stronger if at all is a 9"???

 

Define "serious power" . I know George Baxter took his 4,000# 30th SS convertible well into the 9's, at about 950 flywheel HP with a Strange 12-bolt. Only when he went to the next level did he switch to a 9-inch.

 

don't think i will ever go over 900hp. but say i did have 900hp would my 12 bolt handle that without a problem?? is there a big difference?? and i know what some people get away with drag raceing a 10 bolt all the time. i really just want to know what the limits of the 12 bolt and what the limits of the 9" are and how reliable they will be at 600-800hp?? remember i have a M6

 

Not exactly sure, but i think BigRick's 1200rwhp LT1 is running a 9". Only hearsay though, didn't hear that directly from him. INTMD8's 850rwhp LT1 is running a 12-bolt, and he said in one thread that it "breaks on a regular basis." But he's also running a G-force built 6-speed with that much power so that might have something to do with it from all the shock loading.

 

if you are making serious power then the ford 9" is the only option, lets take a look and see why..
1- you can get a 9" with up to 40 spline axles.
2- aftermarket center sections have billet caps and have through bolt designes.
3- the pinion placement, large pinion bearing diameters and gear cut make it superior to the 12 bolt.
4- you can put a welded backbrace on the 9" housing.
i have only touched some of the design fetures of the 9" but put to test a bone stock 9" against a 12 bolt i really think the 9" is superior.

 

I think the 12 bolt strength depends on car setup and luck. I also have a Moser 12bolt with 33's and the Eaton posi. I broke a side gear in the posi after 2 passes on ET streets, a Street Twin and a 3000 rpm launch with just under 400 rwhp. I don't think it should have broke and Moser is saying I may have got a bad apple with the posi, but they can't say for sure because Eaton is not part of Moser. Just a supplier. But they are working with me nicely and looks like i'll just get a replacement. But now i'll be scared to get on it hard at the track. I think that sometimes the M6's are just too hard on some of the rear ends out there and would be willing to bet that my rear wouldn't have broke if it was an A4. Or at least held up a lot longer. Think theres pros and cons to both set ups. Another being weight and HP loss through a 9" vs a 12 bolt. But if your running BIG power with a 9", then who cares.

Ken R.

 

I really wanted the 9-inch too, but the thought of losing the anti-lock brakes shy'd me away from it. A few years back I almost totalled my car due to a braking situation. I am sure the accident would have been disatrous if it weren't for antilock brakes. Soon after that incident I installed C5 corvette brakes on my car....what a huge difference. On my little S10 truck, the antilockers saved an accident too several times now.

I am sure the 12-bolt is plenty strong for most needs, especially a street car. For drag racing, the posi unit may not be strong enough though. A spool would make it much stronger, but you can't run a spool on the street.

The 12-bolt has a better posi unit than a 9-inch. The 9-inch is untimately stronger due to the positions of the ring and pinion and the housing. But this positioning takes more horsepower to drive it. I ended up with the Moser and it has been pretty good. Comparing the Moser 12-bolt to the stock 10 bolt is a joke once you see the difference in person.

 

Talking about posi failures and 9" vs 12-bolt is like apples n' oranges. Any posi is going to have trouble when you start to approach 1,000hp and are launching on a prepped surface with stick tires. They were just not designed to do that. Has nothing to do with 9" v. 12-bolt though. If you "need" a 9" you also "need" a spool. Unfortunately, this will pretty much make the car a trailer queen. Yes, I am aware that there are people using a spool on the street. But a word of advice: do some street driving in a car with one (a spool) before you decide to go this route. Most will find it completely unacceptable.

Rich

 

Had 2 different 12 bolts and about 3 different sets of gears between all of em All would start quiet and then after few nice shocks from the Street Twin they would get louder.

I did a lot of research on here and LS1tech.com and i think it is safe to say if you have a M6 with a good clutch do not waste your time on a 12 bolt.


9 Inch is the way to go with a 6 speed cars.

 

Most high performance gears are not quiet, they make noise due to the cut of the gears. Richmond gear is a good example. That's wierd how it got louder though, what ended up causing that? What 12-bolts did you have?

 

i have a 3rd gen that goes 9.41 at 146mph and off a trans brake and it's as quiet as the axle in my everyday driver. it's all in the way it is set-up and broken in.

 

That is the truth its all on the install some guys get impatient and dont get the perfect mesh and leave it I have heard cars with 4.10s that are so damn loud and then I hear some that you cant even hear...its all on the install and the break in