Making it harder. You know, my rear-end. Oh, just read the thread...

[Betrayer00GT]

In this thread, I am not concerned about built short block options, or what blower I should use, or if I should use a turbo setup instead of a blower. I am asking about the rear-end, and exactly how to keep it from dying when running forced induction and some drag slicks at the track.

With that out of the way, lets get to it. Quite some time ago, I posted a thread asking about what is needed to "harden" the rear-end of my '00 GT for serious drag racing with up to 600HP at the wheels. Well, I know now that I am going to shoot for a more modest 450 - 500 at the wheels with race fuel, and a good bit less for daily driving on pump gas.

So, I have recently taken the info in that old thread and used it to come up with a Bill of Materials for this upgrade. It turns out the price total is much less than I was expecting. Maybe I have made some mistakes, or cheaped out, let me know. Also, based on my conversations with some local Mustang guys, I have discovered that I can add a Cobra rear brake upgrade at the same time for very little extra cost.

I am not sure exactly when I will get to this, but I am expecting it to be around Summer-Fall of '07, based on the cost I have come up with. If the cost is actually much higher, I will need to move it out further. Since I have some time between now and then, I was hoping to get specific feedback for my current plan of attack. Below is a list of what I am looking at, at the moment. It comes from various online sources.

Item / Mfg / Part # / Cost
31-spline axles and bearings / Alloy USA / 12187 / $209.95
3.73 ratio gears / FRPP / m-4209-f373n / $165.95
Cobra rear brake bracket and rotor kit / FRPP / m-2300-m / $174.88
Diff girdle / FRPP / m-4033-g1 / $177.95
Friction modifier / FRPP / m-19546-a1 / $3.50
Gear install kit / FRPP / m-4210-b / $79.88
Cap studs for diff and girdle / FRPP / m-4034-a / $35.00
31-spline limited slip diff ('03 Cobra OEM) / FRPP / m-4204-f318c / $258.95
Speed cal / FRPP / m-9731-t99 / $89.00

Total: $1195.06


So, I found the Alloy USA axles included the axle bearings and were still a good bit cheaper. If I do not get the axle bearings that way, I need to add the extra cost for the right install kit, too (~$110, vs ~$80).

I also found the limited slip 31-spline diff that was the OEM diff for the '03-'04 Cobras (the one with the carbon fiber clutch plates) for less than $260. That seems like an excellent option to me. Anyone think this one would not handle the occasional track use with slicks? I am not overly excited about a locking diff. I am hoping an LSD model would be good enough for me, I certainly think it is more streetable (IIRC).

Anyone see any of the "little things" I may have missed? I think the install kit is complete enough, and I included the friction modifier in the list. I do not need to get any of the diff fluid, that is why I didn't include it here.

Any specific thoughts/ideas/suggestions?

Thanks in advance, everyone!


:SNSign:

 

[steveb24]

3 quarts of 75w-140 royal purple gear oil. friction mod can go.

 

[Rocketman]

 

[the98stang]

Slap on your mods before beefing up the rear. The stocker might hold up. Then when it blows, replace it.

 

[Betrayer00GT]

Slap on your mods before beefing up the rear. The stocker might hold up. Then when it blows, replace it.

Anyone else think this could work?

Could save a good bit of cash. I do have other things to use it on, after all.

 

[Duke309]

might want to get a tuner instead of the speedcal.

 

[BennyBlown2v]

Anyone else think this could work?

Could save a good bit of cash. I do have other things to use it on, after all.

Don't - not if you're running slicks. Spinning an axle tube would suck, or ripping/tearing a torque box. To fix this issue you can weld the axle tubes, and weld the torque boxes; but, to do the torque boxes properly you'll need to remove the rear end...so take the rear out, have the parts put in and everything welded up.

 

[01Steeda]

While I have welded torque boxes I have a stock rear that has held up fine. I dont kill it off the line though

 

[Betrayer00GT]

Don't - not if you're running slicks. Spinning an axle tube would suck, or ripping/tearing a torque box.

Yeah, I forgot to mention that I wanted to remove the rear-end and get the welding done during the install process.

Any one want to suggest what a reasonable charge would be for someplace to make the welds if I brought the disassembled rear-end in to them?

Thanks again for all the responses!

 

[Mike97gt]

I would

1. weld the tourqe boxes and axle tubes

2. install a 31 spline carrier.. they can be found in explorers cheap at the bone yard.. even independent rear susp. 02+ explorer rear ends work..

3. 31 spline axles..

4. new set of trac-lok clutches, shimmed a little on the tight side of spec with a 8.8 F-150 S spring.. and use as little friction modifer as you can.. only use just enough to stop low speed tight turn chatter.

 

[ADRENLN]

yea, id build the rear first just to be on the safe side. thats just me, ive been trying to play my whole build safe...it cost more to be safe, but thats the way to go.

why are you gonna run race gas for 450-500rwhp?

 

[jivepepper]

I bought the
alloy 31 spline axles for 209.00
used explorer 31 spline diff 90.00
used 3.73's from a ranger 64.00
brenspeed complete 8.8 rebuild kit 65.00
new clutches with friction modifier 50.00
3 quarts motorcraft gear oil. 9.00
--------------------------------------------------------
$487.00


Friend of mine has all the necessary tools and I will install the parts there.

 

[Betrayer00GT]

why are you gonna run race gas for 450-500rwhp?

Well, my current plan is to use the KB 2.1L intercooled kit. Their tech page indicates that 91 octane is only good to an 8# pulley, with all the usual "YMMV" caveates and what not. They indicate 100 octane is good to a 14# pulley. Elsewhere, they document 507 wheel HP using a 14# pulley with optimal timing on a basically stock '02GT. Their upgrade switch chip has a mode that advances the timing to "optimal" from the usual 18 or 19 (can't remember which). I figure I will just use what ever pulley gets me to nearly 500HP on a local dyno using the "Unical 76" 100-octane available at a station a few blocks from my place ($6.99/gallon, so only for track days). Nice and safe. No detonation.

When not at the track, I would just use an 8# (CARB legal) pulley and the normal "CA Premium" 91-octane, which should avoid issues with local law enforcement types who love to "crack down" on "street racing mods".

 

[forum155pl]

If it were me i would run the piss out of it till it broke, then replace it...