I have a 12-bolt in the car right now w/ 3.73 gears, I have a 9" sitting in my shed w/4.10, should I keep the 12 and just get 4.10's for it or swap it out with the 9" Sorry for the stupid question I don't know much about rear-ends.

 

i put a 9" in my car and slowed down .15 in the 8th. around .25 in the 1/4. wish i had gone with a 12bolt or s60.

 

Well the 9" is definately the stronger rear-end. if your car wasn't stalled, i would say keep the 12 bolt, but since your probably making at least 400 rwhp, i would swap to the 9".

 

wanna sell the 12???

 

Since you have an auto I would stick with the 12 bolt.

 

sorry should have specified, the 12-bolt is in my m6 car with head, cammed, full bolt-ons, forged 346. I bought the 9" for the auto, just was thinking of swapping them since the manual does more stress on the driveline

 

hey let me know if you want to seel the 9 inch i will buy it

 

the 9 in is only stronger when spooled, also the 12 bolt on a friend of mine his firehawk is a built 408 procharged m6 is just above 700rwhp and his 12 is holding up just fine, also so is mine with all my mods, if your worried about strength and you want something stronger than the 12, 9in spooled is what you need. I would stay with the 12 bolt

 

cool thanks, I think I might keep the 12 bolt in there just swap out the 3.73's to 4.10's

 

for your auto id keep the 12 bolt... and sell me the 9" (if i had the money )

 

does ur 12 bolt whine? if yes, did it start after hard launch several times be on street or strip?


fuerzaws6

 

Put a 12 bolt into a early Chevelle, Nova, Camaro, etc and you can beat the crap out of it, and not hurt anything. Put one into one of our cars with a torque arm, make a couple 4000 to 5000 dragstrip launches, and I can just about guarantee you'll pick up gear noise. If it is a drag only car, you'll never know or care about the gear noise. Drive your car home from the track, and the noise will drive you nuts. I feel the torque arm stresses the 12 bolt housing, causing distortion. We have never seen this happen with the 9 inch housing.

Exotic Performance Plus strongly recommends the Moser nine inch. This rear is even tougher than the Moser 12 bolt, and the horsepower of the late model F Body cars keeps escalating every year, which requires a very strong rear. With the recent introduction of the 6.2L GM aluminum block and the excellent flowing 6.2 litre heads, the horsepower of these cars is going to just keep climbing at a very fast pace.The nine inch will handle the power, plus we prefer the way the torque arm is bolted to the nine inch in the same way the oem rear-end is attached. (This is the only good thing about the stock 10 bolt...) The Moser 12 bolt uses four short bolts to attach the torque arm, and they have a habit of loosening up, even when loc-tite is used. Why the nine inch is stronger than the 12 bolt. The 9-inch has an internal rear-pinion support that also supports the gear end of the pinion to limit gear deflection under high torque loads. This seems to be the major reason why the 9 inch doesn't start whining after high rpm clutch dumps, when the 12 bolt will pick up noise.The 9-inch locates its pinion gear lower on the ring gear to improve tooth contact, than the 12 bolt does.The 9-inch has a 0.125-inch larger ring-gear diameter and internal pinion support than the 12 bolt does. This is not much of a difference, but it is worth noting.
http://www.exoticperformanceplus.com....html?item=145 Bob

 

unless you are running loads of torque, your 12 bolt will hold up. Either rear end is plenty strong for what you are doing so I would say the effort of swapping them far exceeds the beneft

 

Well put, Bob.

This is probably because the 9" housing can flex all it wants without altaring the relationship between the ring and pinion. There is little to no stress applied to the 3rd member other than the gear's own forces.

 

That makes sense. Bob

 

6speed = 9in auto= 12bolt

 

That's the price you pay for a practically unbreakable 9" when built correctly. I was going back and fourth between the two for awhile before I picked my 9".......sure it takes a couple my HP to turn but I like the added security it gives me.

 

That implies that the 9" is stronger.

 

a 9in is stronger for the shock a 6 speed will put on it !! You dont have as much in an auto as you would in a 6 speed.

 

X2. 12 bolt is all you need for an auto.