9" Rear Losing 30HP?

**BlueMagicSS** · 09-29-2008, 01:00 PM

I've heard from a few people that with a 9" Rear end you lose 30 HP as opposed to a 12 Bolt?? I was wondering if this was true or not?? I've also heard that the 12 Bolt was better for handling and that the 9" was more for straight line performance....??

I'm looking to have a good drag car... but of course I want my cake and I want to eat it too... I want it to be able to handle good as well... which rear end would be better? I'm looking to put in a 454 LSx Stroker with about a 150-300 Shot of Nitrous and a Blower... with a built M6

**LT1 > LS1** · 09-29-2008, 01:04 PM

no, you wont lose that much power. maybe 1-2 hp. nothing noticable at all.

car craft did a direct comparison of the s60, 12 bolt, and 9"..... the power reduction was slim to none.

**BlueMagicSS** · 09-29-2008, 01:06 PM

Originally Posted by LT1 > LS1

no, you wont lose that much power. maybe 1-2 hp. nothing noticable at all.

car craft did a direct comparison of the s60, 12 bolt, and 9"..... the power reduction was slim to none.

I didn't think it would be that bad.... seemed kinda odd to me but I had to ask...

**Bottesini** · 09-29-2008, 01:08 PM

The horsepower lose between the different rear ends is proportional to the power going through them. I have read in an article that the 9" lost somewhere like 3.5% compared to a 12 bolt, but they did not go much into detail about it. Where they measure that 3.5% makes a big difference.

As for handling the 9" might be a bit worse, but the only major difference I could see is that is from the extra weight.

If you really want to put down the type of power your are wanting with a M6 I would defiantly go with a 9".

**Goldcuffs** · 09-29-2008, 05:10 PM

A friend of mine was running 11.40's in his Camaro. All he did was install a Moser 9" and lost a full second! I know this sounds extreme but I helped install this rear end so I know first hand of the loss.

**Zboner** · 09-29-2008, 05:41 PM

dude he lost a full second??? no way

**Hot Black Trans-Am** · 09-29-2008, 05:46 PM

I just installed a 9" in mine. It doesn't feel any slower to me. I did go from 3.42's to 4.10's though. As far as handling goes it seems the same to me. I can't rate tight corners until I get another center section with a limited slip unit. I'm running a full spool for now.

**BlueMagicSS** · 09-29-2008, 06:32 PM

sounds right to me.... I didn't think you'd lose more than a few HPs.

**HB of CJ** · 09-29-2008, 06:39 PM

In auto shop a long, long time ago, the instructor told us to study the blueprints on the slight differences in the design of the rear ends. Then we had examples of the Ford 9 inch and the GM 12 bolt to actually compare.

In theory, the GM 12 bolt may experience a little bit more efficiency due to its more straight-in design, with the pinion being closer to the middle of the ring gear. Whether or not it matters? Dunno for sures.

**Hot Black Trans-Am** · 09-30-2008, 02:19 PM

The most important part of course is the 9" will have the least chance of breaking out of the two.

**squee** · 09-30-2008, 02:34 PM

You will infact lose a small bit of power going through a 9" as apposed to a 12 bolt, but its not really a big deal since you lose weight and add strength.

**Zboner** · 09-30-2008, 02:48 PM

Originally Posted by Hot Black Trans-Am

I just installed a 9" in mine. It doesn't feel any slower to me. I did go from 3.42's to 4.10's though. As far as handling goes it seems the same to me. I can't rate tight corners until I get another center section with a limited slip unit. I'm running a full spool for now.

thats how I am also, not a big deal though about tight turns

**Bottesini** · 09-30-2008, 03:09 PM

Originally Posted by squee

You will infact lose a small bit of power going through a 9" as apposed to a 12 bolt, but its not really a big deal since you lose weight and add strength.

Most 9" are both heavier and stronger then 12 bolts. Not to mention have more parasitic loss.

**squee** · 09-30-2008, 03:11 PM

Originally Posted by Bottesini

Most 9" are both heavier and stronger then 12 bolts. Not to mention have more parasitic loss.

I don't think a 9" is heavier than a 12 bolt...

**Zboner** · 09-30-2008, 03:13 PM

Originally Posted by squee

I don't think a 9" is heavier than a 12 bolt...

there not anymore if you opt for the aluminum center section

**Bottesini** · 09-30-2008, 03:47 PM

Originally Posted by Zboner

there not anymore if you opt for the aluminum center section

With the aluminum center section I have been told it is somewhere around 10-15 lbs difference. Obviously a iron center section is going to be even heavier. Not sure how the M9 weight difference is, but that is only based off of the 9" not a true 9".

**Mr. Luos** · 09-30-2008, 03:52 PM

A 9" with aluminum center section is said to be a touch lighter than the 12 bolt.
No idea how accurate that is though.

I know my 9" with the iron center section is a HEAVY bastard.
But going from the 10 bolt with 3.42's to the 9" with 4.11's knocked .5 seconds off my ET's. Nothing else changed.

The 9" is heavier than the 10 bolt by like 90 pounds (iron center section). I love my 9" though. Nothing to worry about...and I drop the clutch from 6000+ RPM on slicks.

Parasitic loss is roughly the same (with the 9" losing just a touch more) with both rear ends.
The 30HP is probably from the 10 bolt to a 9" on a cam only type car.

**Jays00ss** · 10-01-2008, 06:56 AM

Damn it I knew my Dyno #'s were bad, let me put my 10 bolt back in. NAH!!! I like the piece of mind of my nice little 9" back there.

**SSwt00SS** · 10-01-2008, 08:48 AM

Originally Posted by LT1 > LS1

no, you wont lose that much power. maybe 1-2 hp. nothing noticable at all..

that is the funniest thing i have ever read on this site...

let's clear up a few things for you...

1) going from 10-bolt to either a 9" or 12-bolt will result in power loss greater that "just" 1-2 rwhp.

why is this...it's because both aftermarket rear-ends weigh more than the factory rear. larger dia axles, larger dia rear center section, and heavier all around weight of the material used (IE: thicker axle tube walls) means that you have more weight than before and greater parasitic loss do to having more rotation mass (over the factory 10-bolt). MEANING: it will take more power to rotate than before...

2) now lets consider that most people opt for 4.10 or a deeper set of gears when upgrading to the stronger rear-end. it is a PROVEN FACT that when running a deeper gear, you lose power (at the rear). the trade off is quicker acceleration since the deeper gearing puts and keeps you in the meat of the powerband in the gears.

a person with a 9" and 4.10 gears will show a lower loss of rwhp than a person running the same setup but using 4.30 gears...