CashMoney

iTrader: (2)

I've been reading post after post on which rear end to go with 12-bolt or 9" and From what I can tell 9" w/m6 becuase your hard on your rear end. I never dump the clutch at more than 2K and I don't want the static loss especially since with road racing I'm at all rpm ranges. I'm beefing up the suspension and drivetrain before I make it to the motor.
I've pretty much decided on the 12-bolt becuase they are strong units and allow less parasitic loss in power. Am I right in thinking this way? I've ran 3 runs down the 1/4 and I race road courses alot. I'll probably run it a few times on the 1/4 mile to watch the times drop throughout the upgrading process but 70% of the time it'll be driven on the street or in a road course event.

Any insight would be helpful.

Thanks,
Nate

1BADAIR

iTrader: (1)

The 9 inch makes for easy gear changes if you are that hardcore. The 12 is probably more than enough and will save some rotating mass
The ball bearings in most after market rear ends don't take side load from autoX and road racing very well. I talked to moser a few years ago about this. They said I could convert to tapered bearing if I remember correctly

2MuchRiceMakesMeSick

For road racing I would stick with a 12 bolt.
Its lighter and less rotating weight.

blue01ta

iTrader: (4)

Just for ***** and giggles I'd at least talk to a couple of the sponsors on here. You can get a lot of parts for the 9" now that are lighter than ever. I don't know if they are yet lighter than th 12 bolt but shoould be close. Billingsley sells a really light set up using their own housing, aluminum center section, gun drilled axles, etc. They're not cheap but overall not too bad. It doesn't hurt or cost anything to check and this is still stronger than the 12 bolt. Just another option to consider.

Spenser309

9" is used alot in circle track racing. better safe than sorry. If your going to push over 500 id do the 9" otherwise, id still do the 9" but you could get away with the 12 bolt if you wanted to.

TRex

iTrader: (3)

That is correct, most 9" come stock with ball bearings on the axle ends, so they would need a circle track conversion kit. Usually when an aftermarket supplier puts the 9" style bearings on a 12 bolt, they also put in the ball bearing style.

As others have said, 9" is stronger, and can be made close to the same weight as a 12 bolt with enough money. 9" is less efficient due to the gear cut pattern, uses about 3% more power. Can't really change that due to the positional relationship between the pinion centerline and the diff centerline.

dailydriver

I would try to speak to, or PM Cal (usually on the handling & braking forum). He seriously open tracks/autocrosses a 400+rwhp car with a 9" and race compound slicks.

BillS

iTrader: (13)

I did a lot of research on this when making my choice. You can get the 12bolt with a tru-track, a 9in with a tru-track or a 9in with a torsen T2R. If you have 3 channel ABS and want to keep it then 12bolt is the only choice. 4chanel then either will work. Only the 12-bolts with a spool use the ball bearings and the same for the 9in as they all use 9in ford axle bearings. I went with the 12bolt and it autoxes fine.

dailydriver

Bill, the Truetrac had enough bias for you, or there was no other choice (those Gold road race units or such??)?

02TransAm/Batmobile

iTrader: (32)

im kinda ignorant when it comes to rear ends, . . i plan on purchasin one in few years down the road( when i get the money) so im takin in all the information i find out there, . but i think i've read that 12 bolts are better for automatics and stick with a 9" if you gotta manual, . . . again im basing this on something i read, . . correct me if im wrong

BillS

iTrader: (13)

the tru-track feels the same as the T2r, but the 4.10 gears make it much easier to turn the car with power. there is a lot more pull with these gears over the 3.42's.
Even it there was an auburn race diff, it would wearout to fast for me.