monsterls1

iTrader: (8)

I have been leaning towards a Billingsley street 9"(Moser housing, Strange aluminum center, 4.56, spool, gundrilled, 35 spline axles) over a similarly built Moser 12 bolt. All of my searching has told me that a 6 speed and hard launches will destroy a 12 bolt, but if this is true, then why do I see some of the fastest 6 speed guys on the board running 12 bolts. What are the advantages to running a 12 bolt in high hp cars, other than less drivetrain hp loss? Please enlighten me because i have been going back and forth about this for months and I just want to finally buy one! The car is very light and sees very little street time just car shows and nice days. I should be making about 450 hp after this month, mods are in the sig, and AFR heads and nitrous are coming soon!

camaroextra

iTrader: (10)

well my boss is running an original 1967 12bolt on his forged LS1/80mm turbo/built t56 setup (+/-900hp), on slicks and has yet to break the rear end.

a 9" will suck up a little more power than a 12bolt will, but not a lot more

lafnlt1

iTrader: (4)

it all depends on the combination and the driver, alot has to do with the driver though and how hard they drive the car. i have seen 12 bolts well in the 9's and my car is one.

DSG

iTrader: (1)

The differance in the ring gear size is very little. IIRC the ring gear size of a 12 bolt is 8.875 inches....Please correct me if I am wrong.

gator's 99TA

iTrader: (2)

dave you are right. a 12 bolt with spool is good enough for high 8s easily IMO. dont confuse the OEM GM 12 bolt rearend with a Moser/Strange/etc custom assembly. its much stronger than the old school stuff.

its personal preference. weight and slight powertrane loss are of some issue. the biggest issue for most is the greater choice gear selection in the ford camp.

rocketman442

iTrader: (8)

Why doesn't anyone make a bolt in assembly out of a GM 8.5" 10 bolt? Those are very strong and pretty lightwheight.

gator's 99TA

iTrader: (2)

b/c the 12 bolt is stronger and just as cheap to build lots of aftermarket housings for teh 12 bolt. the oem 8.5" is limited and old at this point.

monsterls1

iTrader: (8)

Thanks guys, keep the good info coming!

DSG- I was thinking the same thing about the small difference in ring gear size, and that is what was making my decision hard also, how could a 9" gear be so much stronger being only .125" larger than a 12 bolt r&p?

alans02z

iTrader: (9)

The fact that the ring and pinion is bigger isn't the biggest part that makes a 9 inch stronger. It has to do with the housing, center section, and pinion location too. Some people say its over kill, some say its not the much better. But the fact is, you can have a race center section and a street center with one having a spool and the other with a posi, and differant gears and change in less than an hour that makes them attractive to some. Also like was mentioned, gear selection is a little better.

OutlawZ

iTrader: (4)

something nobody has mentioned is the fact that the 9" pinion gear is supported in two places versus one for the 12 bolt. The top of the 9" pinion gear has another small steel shaft that rides in an iron housing surrounded by a bearing. And obviously it is also supported at the end near where the yoke mounts to it... so the pinion gear is held in place and won't deflect away from the ring causing massive failure.....

The 12 bolt pinion is just held in the standard way all rearends are AFAIK....

DSG

iTrader: (1)

Agreed, I went 12 bolt because its less expensive, Lighter and me being an Auto I dont shock the rear like the M6 guys.

mvonada

A 9" because of its design will cause a slight loss of hp to turn it.

monsterls1

iTrader: (8)

Anybody else with some personal experience, and good info?

Jeremiah

iTrader: (5)

The 12 bolt will transfer power more efficiently than the 9" due to the pinion location and less recipitating mass. I think the only true benifit the 9" has over the 12 bolt is ease of gear changes and the extra support of the pinion gear like mentioned earlier.