PDA

View Full Version : What's better 9" or 12 Bolt???



RoadFarmer
10-21-2011, 06:58 PM
I was on Speed-tech's website and saw that they offer their chassis kits with either a 9" or a 12 bolt rearend. I always thought a 9" was stronger and better but thought I'd ask you guys want you thought.

LS1-IROC
10-22-2011, 04:15 AM
9" is a better design for strength than a 12 bolt. 12 bolt is slightly less parasitic. If you are planning on moderate hp levels on an automatic car...a 12 bolt will be fine. If you have a manual trans I would opt for only a 9" rear. I built a 9" for my car and they are very easy to set-up.

Nothingface5384
10-22-2011, 04:37 AM
I'd go with a 12 bolt housing with torino style bearing ends, 35 spline bolt-in axle with a wave track or atleast a detroit tru-trac

parsonsj
10-22-2011, 06:20 AM
Farmer, you need to define "better". What's your criteria?

Stock strength? Aftermarket support? Ratio choice? Differential choice?

Let us know what you're looking for, and we can help you out.

RoadFarmer
10-22-2011, 07:01 AM
Farmer, you need to define "better". What's your criteria?

Stock strength? Aftermarket support? Ratio choice? Differential choice?

Let us know what you're looking for, and we can help you out.

Well I was looking at Speed-Tech's website and saw that they offer their chassis package with either a 9" or a 12 bolt. So if I was going to buy a new rearend with say 3.73 gears and wanted to run about 820hp with a six speed auto, which would be a better rearend for the car?

Gitter Dun
10-22-2011, 07:04 AM
The 9" was the stronger rear end back in the day but things have changed. 12 bolts can be built in any configuration now and have less parasitic drag.

IMO, the choice should depend on rear packaging. Are you going to run a watts link, etc....

RoadFarmer
10-22-2011, 07:08 AM
The 9" was the stronger rear end back in the day but things have changed. 12 bolts can be built in any configuration now and have less parasitic drag.

IMO, the choice should depend on rear packaging. Are you going to run a watts link, etc....

Rear suspension set-up would be something like what Detroit Speed or Speed-Tech have to offer.

Gitter Dun
10-22-2011, 08:11 AM
IIRC Detroit Speed and Speed-Tech run track bar so a 12 bolt would not be a problem. It's all going to boil down to personal preference. Either one will suit your needs.
Set it up like the guy in post #3 said and it should be able to handle the power.

Derek69SS
10-22-2011, 08:26 AM
Both have their benefits...

Both can be set up with the Ford style axle ends, so you don't need to run the crappy stock C-clips in the 12-bolt.
12-bolt has less parasitic losses through it, so you're getting more HP to the wheels
12-bolt is a Chevy design, so you won't have to listen to how you "ruined" your car with Ford parts.

9" has the pinion lower so it's easier to get proper driveline angles on a lowered car.
9" has the benefit of easier gear swaps if you want to have multiple center sections set up for different purposes... you could have center with 2.73s for Bonneville or Silver State, 3.50s for street, and 4.88s for drag racing if you want to do that sort of thing.

I went with a 9" mainly for the less-intrusive floor mods for proper driveline angles.

parsonsj
10-22-2011, 09:00 AM
So if I was going to buy a new rearend with say 3.73 gears and wanted to run about 820hp with a six speed auto, which would be a better rearend for the car?That's not a definition of "better". What do you care about? Configurability? Aftermarket choice? Ultimate strength? Horsepower loss? Looks? Pedigree (GM or Ford)? Are you going to weld it up? Or have a vendor set it up for you? None of the above?

Anyway, in terms of background information, the lower pinion of the 9" and a slightly larger ring gear is what gives it extra strength along with the higher hp loss. As others have said, either can probably meet your needs. The 9" has more choices -- in gear ratios, differential choice, axles, housings, 3rd member cases, etc. If you want to swap 3rd members to change gear ratios or differentials, the 9" is a better choice too -- assuming you can give up the 10hp the 9" costs.

vintageracer
10-22-2011, 10:13 AM
You can also consider the GM 8.5 from a G body, a 8.5 inch Big 10 bolt, a 8.8 Ford from a Mustang and their is always the 8 inch Ford.

I and many others have run an 8 inch Ford in Vintage road racing Mustangs for years with no problems. For road racing the 8 inch much lighter than the 9 inch and requires far less HP to turn it.

Lot's of good choices out there besides the all too familiar 12 bolt and 9 inch Ford. It all depends upon how you will use your car the most!

CarlC
10-22-2011, 10:22 AM
I believe it's a question better served in the Drivetrain section.

Nothingface5384
10-22-2011, 11:35 AM
what car is this going in... no mention of it

if its a trianglated 4 link setup and you just plan to go with stock dont bother with an s10/gbody rear and just try to find a 71-72 buick skylark/gs/olds cuttlass

2 reasons for this..they're stock bolt in axles and have 3in axle tubes vs s10/g-body c-clips/ 25/8 axle tubes..

if youre buying an axle I still stay 12bolt over 9 due to less wieght / less power lost and a tad cheaper..

10 bolt with bolt-in 30 spline axles are still a bit better then stock 12bolt with 30 spline clips

only reason i say 12 bolt is because you can go with 33 and 35 spline axles and have a choice of a wave track diff if you plan to make serious power..

68camotion
01-16-2012, 08:45 PM
Preference preference, I don't believe either has a major advantage over the other.