12 bolt or 9in for Autox?
 

I know after my engine mods and 4.10s my 10 bolt is going to blow.

However, I am gearing my car towards more of a handler than a drag car. I plan on going full Koni/strano/UMI suspension.

Well I hear that people that put 9 inch rears or 12 bolts have handling issues (which makes sense since there is a mass change and the oem suspension design is not meant for it.)

So my question is, can I get an aftermarket rear end for handling or should I just roll the dice and keep the 10 bolt and replace it as needed?

Keep the 10 bolt if your primary concern is handling. No high RPM clutch dumps and no drag radials and it should last a while...

The 9 inch, if you are careful (and have deep pockets), should be able to be made lighter than a 12-bolt, and there are more differentials to choose from with a 9" type of center section. My vote goes to that if that is your primary concern...I went with a 12-bolt for fit and finish reasons.

im in the same boat. im thinking of upgrading my rear in the future. i autox mostly, but once in a while hit the strip, or do a burnout here and there. i was debating whether or not to build the 10 bolt - weld axle tubes, TA girdle, torsen diff, etc - or to go with a new rear and not worry about it. from what ive been told, the torsen is only available for the 9in, not the 12. so id lean towards the 9in.

Thanks for the input guys. I just remember a few members here saying how they felt like their car was about to lose control by simply going over a speed hump with an aftermarket rear end.

Street tires and autoX only - gamble on the 10 bolt. Throw a TA cover and stud kit on it, fill it with RP, and call it good. If you stay off the drag radials and hard launches, you have a decent chance it will last. Do up your suspension to totally eliminate axle hop and you should be OK.

who said street tires.....i have koni/stranos and slicks for autox.

I've been through the thought process as well, but I put in a T2R in the 10-bolt in 2001 and have been autox'ing ever since. Still holding strong, and I go to the drag strip occasionally. T2R, solid pinion racer and T/A cover, holding up well.

Viper, what gears are you running, and did you upgrade anything else in the rear end like the axles, cover, etc? I really want a T2R and I'm putting around 380 ft lbs of torque to the ground.

I kept the stock 3:42 gears. I'm running a TA cover and solid pinion racer. Also 405 ft/lbs torque here.

What is it about the upgraded rear ends that causes a problem? I have just started to get into road racing and haver turned many laps with my Moser 12 bolt + 4.10s. Back end feels firmly planted on the ground... in fact, before reading this post I had speculated that it might be to my advantage given the extra weight would help the over balance, if but by just a hair. I should add too, that the track I'm running at is very very smooth, no bumps to get things moving around.

But I'm admittedly ignorant here... so what about it is going to hurt me?

The T2R isn't available in many rear ends. Just the 10 bolt rear ends and the Ford 8.8 inch. I've heard good stuff about the T2R to put it simply and want to give it a try myself. I know there are various Auburn and Detroit TruTrac diffs available for the 9 inch, less for the 12 bolt.

That's it, I prefer the T2R and it's only available (easily for us) in the 10-bolt.

This would be my recommendation. I don't see much of a need for extra strength and weight over a built 10-bolt for autocrossing.

I would get a fabed housing 9in. I would guess this is 40lbs heaver than a 10 bolt. I would get a truetrack. It is gear driven posi. I got mine for 3200.00 with a torque arm. I sold my old torque arm and my cover 540.00. So 2700 for a 9in is not bad. I think the 40 lbs is a small price to pay. Also if you brake a axle the wheel will stay on the car.

You're fine with a 10 bolt. The problem with the 10 bolts is that it doesn't hold well against shock loads, like launching with a 6-speed. Autocross is less violent on the rear end in that manner, I think you'll be fine.

I also run an event that involves launching on not the best of surfaces with Nitto 555r drag radials (probably the best tire for the 100 treadwear restriction). I typically slip around ~3000 rpm.

In this event, having higher gear ratios helps. I think a 3.73 would help me, but I'm not sure how many people are running a 3.73 with a T2R. I think 4.10s would make me borderline shifting to 3rd which I don't want to do.

I'll probably just keep my stock end for the time being. I've had decent success with it so far.

The truetrac and the torson are both gear driven diffs, but there's more to it than just that. The truetrac and the T2R will put power down differently. I would like to say more about it but I'm not really an expert in this subject. I do know they are quite a bit different handling wise though.

FYI Running 4.10 with T2R will require some modifications to the T2R unit. So it take a little more work to set up. Usually 3.73 is good choice, specially if in the future you plan to do track day type events. Also when you go to 4.10 the gear pinion is smaller so there is more of a chance to breakage due to the decreased mass. Again it is all dependant on the events you attend. For instance in my local Auto-X group run on fairly small lots so the courses are tighter, the 3.73 helps in the slow corners and I can run most courses in 1st gear with a 6800-7000rpm rev limiter. On track days at the local track I can take the car to around 120+mph on the rear straight without having to shift to 5th gear. The one track is fairly fast so I can run the whole place in 3rd gear and go into 4th on the back straight. Less shifting is faster. But if I need to i can always downshift to second in 2 of the slow corners so I can exit the corners a bit faster.

BTW I'm currently still on the stock differential but I will go to an auburn racers differential soon (assuming I keep the car :'(). There has been some quality issues surfacing with the Torsens T2R differentials.