I know that most will say not to do it but my question is at what point in Hp does it happen most often or is there ample power from the factory to hose it? Going w/RII's and I have an auburn diff, would I really be running a risk of breaking the stock rear with a gear swap? The car will see limited track time and I'm not pushing gobs of HP and TQ. But to really get a good 1/4 mile, no disrespect to anyone, I would need 410's I'm thinking. I'd like to run low 12's high 11's in my daily driver(unrealistic?). I'm guessing my answer will be that it would be the beginning of the end for my 10 bolt? or will is just make some noise?
I'm at 375 right now but have some heads on the way. I should be in the 400 tq 420 hp range after a good tune (hopefully) 450hp and 410tq would be

 

Well, to run a high 11, you really need a good hard launch... which almost automatically says "Bye Bye 10 bolt" in an M6. Hoping the 10 bolt holds in an M6 that runs 11s is like playing russian roulette with a semi-auto. I guess you could hope for a lucky jam.

You also need to drive it like you stole it... not lifting at all when you shift. And I'm case in point on that one. Not only is that hell on your transmission, but it is also hell on everything in the drivetrain, including the rear end.

It doesn't really matter what your HP level is, as HP isn't really what kills the 10 bolt... it's traction. I destroyed my 4.10 ring & pinion with 337 rwhp. Launched at 3k rpms on Nittos, and it stripped over 8 teeth off the ring... that was that, it was time for a 12 bolt.

 

I am guessing that regardless of what gears you run, with that kinda hp & sticky tires, your diff will be toast soon at the track. My friend runs 4.10's in his stock 10 bolt, but he also doesnt EVER take it to the track nor does he drive it hard.........another friend who "had" the Auburn diff in his '02 Firehawk toasted it with stock 3.42's, never going to the track and just driving spiritedly now & then. My suggestion (as always) is get a 12 bolt or 9 inch.

 

I would look at it this way gears, cover, and install are going to run you 7-800 bucks. Chances are you will break it sooner or later, even if you never drag raced everyone I've know with 4:10's eventually they break. If you look at the gears themselves you can see why they are super thin. So when they break you are out another 600 to get them fixed so now your at 1400 and those will break eventually too... You see where I"m going with this. I wouldn't touch that rear unless it was with an 8.8,12 bolt or 9inch. 3:42's give you a much better chance at survival and if it does blow up you can find a takeoff rear for probably around 400.

Again just my .02 but you keep asking for it

 

like tranzor said ealier, there is no horsepower level, its just on how hard you drive it. for me it was the posi, not the gears. went to a locker 9 inch and have never looked back. do yourself a favor if you are going to race the thing just go ahead and save the money to buy a 12 bolt or a nine inch, you will thank yourself in the long run trust me!

Why do something twice like just about evryone else on this board including me when it comes to gears, just do it right once and call it a day.

 

"like playing russian roulette with a semi-auto. I guess you could hope for a lucky jam. "

Ok had to ask, great responses though

Another question how do you know if the auburn is toast? I was told if its spins posi then its ok. So I went out this morning after dropping the kid off at day camp and found some nice clean pavement to mark up. Made two passes using different techniques. As always I rev the motor a little then lift off the pedal and intiate the burn. First pass I held it to the boards boucing off the rev limiter until it spun all the way out of first gear. Went back to look and there were two nice very long strips for the entire burn w/ my patented fishtail S'. So for the second pass I move up the street a little and do it again this time reving the motor thru the burn instead of holding it to the boards. I like to hear the motor rev while I'm smoking rubber, I usualy dump into second while I'm doing this but this time it was a scientific test so I rev'd it out of first. Didnt go back to look how ever as there was a person in their front yard 200 yds away from my last burn. Didnt want any trouble.

 

I have to agree with the others (save and buy a 12 bolt or 9"). But my experience (or luck) is that they can hold up. I first upgraded from stock 3.42's to 3.73's. They lasted a year and a half then I broke two teeth of the pinion. Yes the pinion and not the ring gear. I then went to the 4.10's. They lasted 4 years. This was all still when it was a daily driver and strip car. I replaced them when the posi unit finally went because I found one tooth on the ring gear with a chip in it. It now is not a daily driver and has 4.10's with a lock-rite locker and the TA girdle still in the factory 10 bolt housing. My car when was a daily driver had the 4L60e (A4) and now that it is not a daily driver has a TH350 (A3) with a manual valve body.

 

People have been saying that an A4 car can hold up with the 10 bolt a lot longer then the M6 cars..........makes sense I guess.