9-Inch Rear: ideal specs for a 9-sec street/strip car

[GN SBS]

Hi folks,

I'm building a nine-inch rear this winter and would love feedback from folks who've done this swap on how to spec it out. I haven't decided on a vendor yet, but I'll be ordering a drum-to-drum setup and selling my current rear complete.

I'll be launching off a transbrake (4L80E is going in at the same time as the rear) and will be running high nines, but would like to build the rear to last deep into the nines. Would love your feedback on a couple of areas:

Differential

• I drive to the local dragstrips and don't want a spool-- is a Detroit locker going to be my best bet?
• What other options would you consider? I'm assuming none of the Eaton / Auburn posis can hold up.

Axles

• Do I need 35 spline axles for my application?
• Is the weight savings from gun drilled axles worth the cost?

Gears

• Given that I'll be running a 4L80E, what gear ratio would you go with and why?

Brakes

• Disc or drum? Discs are considerably lighter and stop better from speed, but I do still want some ability to hold boost at the light for events that don't allow transbrakes. Can any of the disc brake setups hold boost at the line? The cost difference between disc and drums isn't much when ordering drum-to-drum rear.

Other

• What else haven't I thought about that I should? (for example, a custom driveshaft is on my trans to-do list)

 

[HotAirGN]

I put a Moser 9" in my regal and built it for a mild street application where I told the builder it needed to be streetable but also handle 650hp on a t-brake.
To do this the 9" has 31 spline axles, Nodular case, and a custom built detroit locker (was told the clutches where changed to handle the t-brake) and I ended up with 3.91 gears. That with a Wilwood Rear Disc Brake setup cost me 2 grand. I was just going to buy each piece and assemble my self but I'm glad I didn't. Everything works fine for my application so I'm happy with the price and product. I was discussing 35 spline gundrilled axles with my engine builder and since its not a full on drag car I can survive better on the treet with what I have. The Rear came from Spraker Racing

 

[craggar]

I have a M9 from Moser, Strange alum center section, 35 spline gun drilled axles, daytona pinion support, spool, and Wilwood disc brakes.

The gun drilled axles are lighter but not a lot. I lauch at 4800 rpm on the brake and haven't had a problem at at all.

I don't mind the spool on the street but a lot don't like it so I would suggest the DL for you. I've had them in low 10 second 3800lbs cars with no problems.

My combo isn't a turbo and hits harder then most turbos which is why I went with the 35 spline. You are probably pretty safe with the 31 splines.

I would guess with yours being a turbo car and having the low 1st gear in the tranny I wouldn't go with anything more then a 3.73 gear. There are calculators on line that can help pick your gear ratio.

 

[GN SBS]

• Do I need 35 spline axles for my application?

Found a nice formula in Moser's tech site on this part of my question: Max torque for axles = (torque of car) * (first gear ratio) * (rear end gear ratio) * (90% efficiency). Their axles are rated as follows: 31 spline = 7,000 ft-lbs; 33-spline = 8,200 ft-lbs; 35-spline 9,600 ft-lbs.

So with the 4L80E's 2.75 first gear and a 3.42 rear it would take approx 1,200 ft-lbs to get near the 35-spline limit and about 1,000 ft-lbs to get near the 33-spline limits.

 

[Scott Atk]

Quick Performance doesn't charge any different... you just pick what spline you want. I chose 35. Cant see any downside.
Also, you will probably find the Detroit Locker more annoying on the street than a spool.

 

[cruzn57]

second Quick performance!

they were very helpful,
I went with 35 spline, pro gear, daytona support, 1350 yoke, strange case, disc brake,and narrowed 2in, from std GN width.

 

[Awesome T]

Try a Detroit Locker car before you go that way

I have the rear end you want in my car, with a Detroit Locker. I did that to handle the power, but the DLs are a bear to live with. For occasional street use, you'd be OK, but if you really want to drive it a lot like I do, the chattering and studdering around slow corners is a pain, and I guess a lot like a spool. Also, after backing up the locker needs to spin a bit to engage, and then it chunks into gear. Not too civilized, but the price that you pay for the security that it won't grenade. Have heard good things about the Detroit True Trax(?), which is a step down from the Locker, but will hold good power and not as brutish. I may swap one in to give it a try. HTH.

 

[GN SBS]

Also, you will probably find the Detroit Locker more annoying on the street than a spool.

but the DLs are a bear to live with. For occasional street use, you'd be OK, but if you really want to drive it a lot like I do, the chattering and studdering around slow corners is a pain, and I guess a lot like a spool. Also, after backing up the locker needs to spin a bit to engage, and then it chunks into gear. ... Have heard good things about the Detroit True Trax(?), which is a step down from the Locker, but will hold good power and not as brutish.

Thanks for the real world experience guys. If anyone has other experiences along these lines or with other options like the True Trax do chime in.

The torque ratings of the various differential options is something I'm going to ask about when calling Moser, Quick, etc..., maybe I won't need the extra strength the locker provides.

 

[Quick Turbo V6]

Here is my Strange 31 spline axle from my car. It ran 9.37@141 the run before this. I was leaving @ 10lbs off the brake. I would go with the 35 spline axles.

HTH,
Scott

 

[GN SBS]

My thanks for all of the thoughtful comments-- any thoughts on the disc vs. drum brakes?

 

[oldtimer]

Here is my Strange 31 spline axle from my car. It ran 9.37@141 the run before this. I was leaving @ 10lbs off the brake. I would go with the 35 spline axles.

HTH,
Scott

I went with Moser 40 spline gun drilled with spool. If you've ever seen a spooled axle car break an axle on launch, it's not pretty. I went for the safety factor !

George

 

[Quick Turbo V6]

I went with Moser 40 spline gun drilled with spool. If you've ever seen a spooled axle car break an axle on launch, it's not pretty. I went for the safety factor !

George

Yeah my car is getting 40 spline gun drilled axles & spool. I had a spool with the 31 spline axles too. It broke right off the line. I have a video of it, the wheel just wobbled alittle . I drove it back into the trailer.

Scott

 

[John Wilde]

Here is my Strange 31 spline axle from my car. It ran 9.37@141 the run before this. I was leaving @ 10lbs off the brake. I would go with the 35 spline axles.

HTH,
Scott

Damn that is nasty!!!

 

[Quick Turbo V6]

Here is a link to the video. Not the best but you can see the left wheel wobble after the launch.

YouTube - Broken axle

Scott

 

[Alky V6]

If the Tru Trax is the carrier with the worm gears in it. Stay away from it. Not good for heavy drag racing. When they go, they are very messy. Running a spool on the street is not a big deal compared to the clunking of the DL.

Dragging with the 4L80E, you want to be crossing the finish line at the top of third. You should not be setup to have to use OD gear in a drag run. Setup your rearend gearing accordingly.

I would go with the discs. Safety is always top priority with me. The discs stop so much better than the drums. When I had the Ford drums on my Moser 12 bolt, I was always paranoid about my stopping power at the end of the 1/8 mile track that I frequent. I would almost always have to use the complete shut down length of the track. After I switched to discs, I no longer think about it. The car stops on a dime, compared to the drums. I can concentrate on other things.

I would go with at least 35 spline axles. Judging from your requirement of possible deep 9s.

Driveshaft upgrade is a must!

 

[lhbarrett]

Alt axles...

Have you considered an alternative, like a 12 bolt, Dana 60 or a built 8.8? It might be some what less expensive. Use less HP to operate it and is available with several types of posi units. You could also find a 8.8 used from a Ford racer...wow a Mustang/ Ford part in a Buick??

Currie Enterprises Dana 60

 

[GN SBS]

Quick bump for Monday-- thanks again for all of the thoughts and keep 'em coming. -Scott.

 

[WIKEDV6]

I am in the same boat, very similar power range build with; Stage II, 4l80e and Ford 9". This is mostly a street driven car. I don't want to go with a spool and I don't like the clunk and banging of a locker.
I was told by a buddy of mine that there is something called a "Soft Locker" has anyone heard of this? It's a locker setup that is much quieter and made for street applications. I haven't looked into it yet as I am still finishing up the motor end of it. I was just wondering if anyone ever looked into this, so called “Soft Locker”

Thanks
Prasad