HP52TA

iTrader: (4)

With my recent upgrade to an LS1 my built up 10 bolt is going to start feeling stressed, so it is time to start thinking of a rear end upgrade. With going to this expense I want it to be the last rear needed for this car, thus the 650 RWHP rating. This should be sufficient to handle a future supercharger or turbo upgrade. No plans for this car to go beyond that.

Tranny plans are to stay with a T56 stick, upgrading it as power development increases. Rear suspension consists of SFCs with soon to be installed Spohn torque arm with x-bar mounted to the SFCs. Plan to maintain the stock rear suspension configuration, with the chrome moly arms already installed throughout.

The car is and will stay street / strip so no dedicated drag rearend wanted. Drag radials and 5K RPM clutch dumps will be in its future. Wheel upgrade will follow rear end purchase, with a deep dish 18" wheel and the widest tire possible without tubbing desired.

Not set on either a 12 bolt, 9" or the Dana 60, so all options are open. Would like to stick with the LS1 rear brake setup to keep costs down, but is not a must. Current gear ratio will remain 4:11 until forced induction comes into play.

Lets hear your recommendations and past experiences.

sofakingdom

iTrader: (1)

I'd recomend the 12-bolt; while not the "strongest" of the 3, it's by far the most practical. Fits the car the best, uses the least parasitic power, yet has good aftermarket support.

Obviously whichever you go with, it'll have to be one of the "custom" aftermarket setups specifically engineered for this chassis, with the ttorque arm provision. Which BTW fits the 12-bolt better than either of the others as well.

AlkyIROC

A Dana 60 is nice but it's big, heavy and overkill for what you need. Pick a 9" or 12 bolt. Both have their own advantages and disadvantages so one isn't always better than the other.

I'm probably pushing 800-1000 hp and just use a 9". Lots of goodies in it but it's still only a 9".

If you have the money and plan on making really big power later in the future then just invest in a Dana 60.

It's hard to say street/strip in Calgary now that Race City is closed. Need to make the trip to Edmonton or Medicine Hat now to get track time. I run too fast to go to Medicine Hat unless I pay the extortion fees and join NHRA. All my future runs will have to be in Edmonton.

articwhiteZ

iTrader: (56)

for the best all around rear. i would have to say 9"
holds up to just about anything
and rear end gear swapping. is done in about 40 min by your self.
(if you do that alot)
and there are more parts.for it. in every city then any of the others!

thats just me

HP52TA

iTrader: (4)

Thanks for the input guys.

I am in agreement with the Dana 60 being overkill at these power levels, so think I will remove it from the equation. It seems like such a huge rear end as well and the extra weight I see as a downside.

Being a bit of a purist, is the only thing pulling me away from installing a 9". I like the 3rd member quick replacement, but not sure how often I would be changing gears with the 6 speed. My thoughts are, set up the gearing for 4th gear 1/4 mile times and have the other 2 gears for high speed and cruising.

So what about axles sizes for the 12 bolt and 9". Is there any calculators out there to determine the appropriate size for the power level?

Yeah, the loss of Race City really sucks. It is only 5 minutes from my house. Haven't made it out there very often with the car due to all the engine building I have been doing, but had the GC SRT8 out a few times for some fun. This is part of my rear end concern, with now having to drive a distance to/from a track, I don't want to be stranded with a broken rear...

sofakingdom

iTrader: (1)

Stock size is almost certainly adequate in either case.

Yeah the quick gear change, along with the variety of aftermarket support for the platform, is the main advantage of the 9" design. While an actual Frod 9" is a steaming bucket of excrement (the ONLY vehicle I have ever personally witnessed burn to the ground because its rear end caught fire, was a Frod truck with a 9"), as a platform it's a whole different story. But it doesn't fit this chassis as neatly as the 12-bolt does, and if you don't need the gear change feature or the ability to handle HUGE torque with sticky drag-racing tires, then it doesn't have much extra appeal.

AlkyIROC

Like I said, they both have advantages and disadvantages. I think the 9" would have the advantage though. Huge amount of aftermarket components make it a much cheaper diff to modify and improve upon.

The 12 bolt uses 30 spline axles but can be upgraded. The 9" uses 28 and 31 spline from the factory but I wouldn't even recommend a 28 spline aftermarket axle for any kind of performance. Depending on your power level and which tranny you intend to use, a 35 spline is probably a good choice. That means an aftermarket center and posi/spool also to handle the larger axles.

The HP loss through the 9" and 12 bolt is different but unless you get actual numbers off a chassis dyno, you probably won't notice the difference.

Weight? I use a Moser aluminum bolt through center. Aluminum spool, aluminum Daytona bearing support. I can lift the center in with one hand. The factory iron centers do have their limits. The N cases are not that great compared to a basic aftermarket case. I cracked my C7AEW case pilot bearing support when the car was in the mid 9's. I've seen them break and explode the diff in heavier vehicle that run 11-12 second 1/4 miles. When the pilot support breaks, it spits the pinion out the side of the diff.

With a 9", you buy a posi or spool for the axle spline count you want to use and it's the last one you'll need to buy. You can put 2.50 gears or 7.00 gears on the same carrier unlike a 12 bolt where you need the correct series.

If you have the money to buy and extra case, gears, posi/spool, doing the gear swap can take less than an hour. Jack up the car, pull the axles, take off the driveshaft, drain the oil (requires a drain plug install) and pull the center out. Everything is set up in the case. With a 12 bolt, a gear swap is very time consuming since the ring and pinion need to be removed and set up every time.

I've gone through a lot of gear ratios in my car and have found 4.86 to work the best for my combination of parts however I don't have to drive it on the street either. Diff is set up and I don't have to keep playing with it.

IROC315

iTrader: (9)

I agree on the nine inch. Both my cars are getting one. Ordering one for my 4th from midwest chassis. I don't know the truth to it but the 4th gen guys say the 12 bolts become noisy after a few hard launches. Not a fault of the 12 bolt but how the torque arm mount is done on them. Don't know the truth to this.

red406

iTrader: (4)

Before my car was back-halfed I had a Moser 9" housing. The upper bolt for the torque arm bracket beat a dent in the floor. My car was lowered with Intrax springs. I think for this reason the 12 bolt might be a better fit.

UnstableAviator

My 9" also dented the floor. No big deal for me personally, I actually "enhanced" the dent for some extra clearance.

I still vote for a 9" though, I've been running mine since 2003 and its held up well. I bought a used center section, and the posi finally wore out and I've got I'VE apart for a rebuild now.

HP52TA

iTrader: (4)

Could you guys post some pics of the 9 inch floor dents required. Sounds like nothing more than a few goods swipes with a BFH.

My car is slightly lowered as well so I would appreciate knowing what I would be getting into.

Thanks for all the great info.

red406

iTrader: (4)

I don't have any pictures of the spot where the bolt head touched the floor. I wondered if I counter sunk the hole in the bracket and changed the hex head bolt to a flat head if it would clear. Never had a chance to try it.

I forgot to mention that my edelbrock torque arm rubbed the driveshaft tunnel with the 9". Stock torque arm fit great.

Tony89GTA

iTrader: (7)

I had to make a custom bracket for the torque arm to mount to the rear(SPOHN setup), still had to dent it but wasn't as bad. I kind of wonder if the dana 60 would be better just for the torque arm part, the 9" is still a friggin heavy rear.

Seafarer12

I vote for a 9 inch just beause the ease of working on them and the aftermarket. That stick will be rough on that rear end.

Aaron91RS

iTrader: (2)

These threads get very old when a search will yield all the answers.
I run a moser 9" with ls1 brakes.
It dented the tunnel like everyone said. I didn't even know it did it till I looked under it one day. Oh well "self clearancing" and a non-issue.
A 9" can have 4-spiders and 3 pinion supports, bigger ring gear and is in EVERY way stronger then a 12 bolt.
I can cram 12bolt guts in to an 8.5 10 bolt if I want or I can just run a 12 bolt. Either way they usually whine after a hard launch on a powerful stick car.
They are lighter, but I can put all alumnum guts in the center of a 9" and make it light too. Of course aluminum is softer and not really for a street car because it will wear tolerances.
Therefore bottom line is strengh wise a 12bolt has zero benefits on strengh and only possibly a few pounds lighter.
It boggles my mind to this day why there is even a 12 bolt vs 9" debate over and over and over when they both cost about the same.
Buy the moser 9" and be done with it.

Of course it also boggles my mind why anyone runs a 3rdgen 10bolt on a mild car when a junkyard 9 bolt is $150 and stronger. People do weird things everyday.

BTW my friends 4thgen went 11.05@119 on 324rwhp on a 10 bolt.
A 650rwhp car should be very impressive.

IROC315

iTrader: (9)

Over on ls1tech it's 9" vs 12 bolt vs S60 which is Strange's dana 60. Lots of guys ordering them. It's a cheaper option in some cases (at least for the 4th gens) and looks stock. Only larger. They don't seem to have the issues the 12 bolts have.

IROC315

iTrader: (9)

Few pics of a S60 next to stock 4th gen rear that was going in someone's 4th. I haven't asked but I believe they can make it 3rd gen width.

heat seeker

iTrader: (5)

I agree on this......I've been running a 9-bot on my car and you can see in my sig.....it holds up quite well. However, the posi is the weakest link on the borg warner, so I ditched it and ordered a spool from Australia and haven't had a problem yet. Some are against a spool........and I can understand, but I haven't had any problems.