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SUNNY Z

Ford 8.8 IRS Conversion

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So if you've been following, my car is hard on rear end parts (LS1 - 6 speed - slicks).

 

I just broke an input shaft to the diff, and I don't plan on changing how I drive the car - so don't even suggest that.

 

2012-09-28_21-48-31_193.jpg

 

2012-09-29_16-03-15_252.jpg

 

2012-09-30_21-38-45_184.jpg

 

2012-09-30_21-39-19_823.jpg

 

I'm curious if an R230 is even beefy enough? I've seen a handfull of LS1 240sx guys making a little more power than me, but having the same issues with an R230 axle.

 

I'm leaning more toward a ford 8.8" IRS from a cobra/t-bird/explorer pumpkin due to the vast availability of gear ratios and LSD's.

 

I know there's been threads started on this before, but no one seems to ever follow through, so theres no info!!!

 

I'm going to try to source one locally and start experimenting this winter I think.

Edited by SUNNY Z

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Doing a little reading about the 8.8 and swaps. I found this on an S2K board

 

Its a 2007 ford explorer diff cover. Could prove useful. this is part number 7L2Z-4033-B

 

211mjwi.jpg

 

IMG_20110710_181459.jpg

 

IMG_20110710_181507.jpg

 

From V8S2000 board:

 

"Ford 8.8 IRS Info

ALL 99/01/03/04 Cobra axles have a 28 Spline outer that goes into the hub

 

99 Cobra axles have a 28 spline inner that goes into the diff

 

01 Cobra's came with stronger axles than 99

 

01/03/04 Cobra axles have a 31 spline inner that goes into the diff

 

03/04 Cobra's came with stronger axles than 99/01

 

03/04 Cobra's came with Carbon kevlar clutch packs

 

03/04 Cobra's came with larger pinion flange than 99/01

 

All Cobra's came with limited slip

 

There was not a 2000 or 2002 Cobra released on the american market.

 

 

 

The 8.8 IRS was offered in the following vehicles

 

99/01/03/04 Cobra

 

1989-1997 Thunderbird Supercoupe (All Posi-traction)

1992-1997 Thunderbird V-8 models with rear disc brakes(some posi-traction)3.08, 3.27

1992-1997 Lincoln Mark VIII (All aluminum carrier, most non-posi-traction) 3.07, 3.08, 3.27, 3.55, 3.73

1989-1992 Mercury Cougar XR-7, supercharged V-6 (All posi-traction)

1993-1997 Mercury Cougar V-8

 

02+ Explorer/Mountaineer = 3.55 and 3.73 open, 3.73 LSD , 31 spline

 

To determine the gear ratio, and whether or not the unit has posi-traction, look at the tag that is attached to one of the differential cover bolts. The first 4 spaces signify the gear ratio and whether or not it has posi-traction. If the unit has posi-traction, then the second space will have an L in it representing (limited slip), the remaining spaces specify the gear ratio. For example, 2 L 7 3 means posi-traction with a 2.73:1 gear ratio. Most people pay a salvage yard between $300-$400 for the donor parts. Also, Ford Motorsports sells a 15lb. lighter aluminum carrier with gears and posi-traction for around $650.

Edited by SUNNY Z

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I thought I posted this but the post didn't go. Check in with 1QUICKZ; he has an 8-second (1/4-mile) IRS 280z with a 12-bolt Corvette diff and his own custom adapters. He's best buds with jnjracing, the guy who only puts front wheels on his z so he can park it easier in the pits.

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What do you suggest I upgrade to? Billet input stubs? FORGET that. I'm not spending a dime more on custom one-off parts that are still inherently weak by size.

 

Also, I'm pretty much done with the nissan diffs. Way to hard to find parts for, suuuuuper limited gear selection, even worse LSD selection.

 

Also, I'm not done with this car - it will get more power in the future, so I'm not just going to put a band-aid on it, I want to FIX the problem.... Which might be more of a project than I can justify right now. However, I'd at least like to look at other diff options.

Edited by SUNNY Z

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Hp/torque at the rear wheels? 1/4-mile times? I am curious what power level would cause the input-shafts to fail thus. Perusing other threads of breakage of rear-end parts, the OP's reported mishap strikes me as rather unusual.

 

For maximal availability of ratios, the Ford 9" appears to be the favorite. There are vendors such as Kugel Komponents who make hot-rod-oriented IRS using the 9". Their stuff is pricey and the setup is like a Jaguar or C3 Vette, with the halfshafts as active suspension-linkages. But their approach to a "narrowed" Ford 9" center-section could be adapted to a Chapman-strut suspension. Then your problem would be finding halfshafts of the proper length.

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The text you posted on the 8.8 axles, about the halfshafts getting stronger from one model year to the next tells me they are weak too. If you are looking to put even more power and shock into your driveline than you have now, screw the IRS, go get the Ford 9" and a 4 link.

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Hp/torque at the rear wheels? 1/4-mile times? I am curious what power level would cause the input-shafts to fail thus. Perusing other threads of breakage of rear-end parts, the OP's reported mishap strikes me as rather unusual.

 

For maximal availability of ratios, the Ford 9" appears to be the favorite.....

 

Approximately 450hp/450lbft. This was a 4500RPM launch (not clutch dump) on slicks. I have the 39 spline stub axles and companion flanges, and a 3" steel driveshaft. It makes sense to me that the weakest part would fail?

 

There are several guys on LS1tech with ~500whp breaking R230 input stubs.

 

 

The text you posted on the 8.8 axles, about the halfshafts getting stronger from one model year to the next tells me they are weak too. If you are looking to put even more power and shock into your driveline than you have now, screw the IRS, go get the Ford 9" and a 4 link.

 

 

Well with that logic, I should probably skip the 8.8, skip the 9" and go straight to a Chevy 14 bolt, or strange S60 - because they're both stronger. :rolleyes:

 

 

 

Ford 8.8 Axle diameters

-28 Spline axle shafts with a 1.29" diameter

-31 Spline axle shafts with a 1.32" diameter

 

R200 Axle diameter

(splined diameter)

-30mm = 1.18" diameter

 

R230 Axle diameter?

- someone lend me a hand here?

 

Even the 28 spline has a .1" on the r200 stubs, which is 9.3% increase in diameter. the 31 spline is a 12% increase in diameter. This doesn't even factor in the availability of upgraded materials.

 

 

I plan on doing this swap with a budget in mind.

I know I can pick up an 8.8 housing for $300 max, with the cover i need, or for less, +75 for the cover.

I will be able to make all the mounts I need.

The only other component will be the Inner CV joint, which I have already talked to the Driveshaft Shop, and they said that they have an input stub with a CV joint on the shelf - which can be mated to the bars that I already have - If the length is compatible. However, they can always be shortened, which I believe will be the case, since the 8.8 is ~11" wide, where the R200 is (narrower).

Edited by SUNNY Z

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Well with that logic, I should probably skip the 8.8, skip the 9" and go straight to a Chevy 14 bolt, or strange S60 - because they're both stronger. :rolleyes:

 

Point taken, but I'm just trying to point out the next weakest link, the stub axles, something a solid axle eliminates by definition.

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Point taken, but I'm just trying to point out the next weakest link, the stub axles, something a solid axle eliminates by definition.

 

This is true. I'd hate to break one of those billet stub axles.... that would be really expensive.

 

I only really have one more drag strip event to go to this year where I'll have the slicks on. I'll probably just put another input stub on that half shaft, put it all back together, and start sourcing parts for this winter. Luckily I have 2 spare drivers side stubs, and one passenger. So I can go to the track with one of each :lol: . Hopefully It can survive another 20 or so passes this year.

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Well I just took the first step and ordered the explorer diff cover. It was like $75 to my door. Worst case I can find an open diff for ~$100, weld it, and I'd be right back where I am now, only with stronger input stubs. Granted I'd have a little added cost of a new driveshaft, and CV mods.

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Spoke with the DSS today. They FOR SURE have the CV joint and internals to convert the 36 spline bar to the ford CV.

 

I'm looking very hard at the 31 spline explorer units. Im hearing that the posi units arent the best, but there are others out there for a reasonable figure that are (tru trac). These are surviving in 1000+ hp cobra's (tanks) that have over 1000# on my go-kart.

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SUNNY Z:

 

Is that the 300ZXT half shaft stub that goes into the center section that SNAPPED? Which stub axles were in the car when the stub let loose? Was that a R200 center section/differential that the stub was inside? What do you figure was the amount of torque applied to the stub? Which engine and trans are being used? Please advise. Thanks.

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SUNNY Z:

 

Is that the 300ZXT half shaft stub that goes into the center section that SNAPPED? Which stub axles were in the car when the stub let loose? Was that a R200 center section/differential that the stub was inside? What do you figure was the amount of torque applied to the stub? Which engine and trans are being used? Please advise. Thanks.

 

Yes, it was the Z31 input stub in a welded 3.54 R200 Long nose. I have the chequered flag racing 39 spline stub axles in the car.

 

I'd guess 450 lbft* 2.66 first gear* 3.54 final gear = 4237 lbft/ 2 = 2119 lbft/ axle

 

This is an LS1 and T56. I might also add that I was on a 26 x 8.5 x 15 MT ET drag slick

Edited by SUNNY Z

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Ideas for mounts from the LS miata crowd

 

http://ls1tech.com/forums/12511950-post13.html

 

Another mounting solution, as the stock cobra covers are known to crack.

 

http://www.lpwracing.com/Instruction/LPW_ULTRA_IRS_Installation.pdf

 

Kinda pricey though. About $200-250

Edited by SUNNY Z

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SUNNY Z:

 

What makes the Ford 8.8 IRS -31 Spline axle shafts with a 1.32" diameter, stronger than the Z31 Long Nose IRS differential? I have beefed up a 240Z with the Z31 Long Nose and beefy stub axles. Up till now was going to go to DSS to get the BEST CV half shafts with the best materials available for same. I have built a SBC 383 stroker with the absolutely best components and looking for 500+ HP/TQ. Really do not want to snap any rear end components. Looks best that I get tires that give/smoke under extreme torque.

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I already covered this in THIS thread.

 

The diff is plenty strong, but the stub shafts going into the diff are are simply smaller.

 

Smaller = weaker.

 

If the input stubs were offered in a different material, then it might be sufficient for now. However, they aren't. The ford stubs ARE.

 

It is a possibility that the stub that broke wasn't as good as others. However, I'm ready for a limited slip, and if I'm going to pay upwards of $1000, I want something I know won't break.

Edited by SUNNY Z

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SUNNY Z:

 

Looks like the best bet is the later year Cobra differentials. Research first then invest if they spec out OK.

 

Except that they cost nearly double what the explorer diffs do, and have probably been beaten 10x harder.

 

I started some mock up tonight with my explorer diff cover. I found that the mounting bolt holes are spaced roughly 14" apart, and that makes them fall nearly dead-center with the uprights that support the rear of the A-arm (not sure of term).

 

Here's a picture of as high as I can get it without clearancing the frame.

 

2012-10-04_21-05-47_182-1.jpg

 

It does have large ears on the cover (rear mount) though, so the 4 bolts on the caps for the a arms would have to be removed to remove the diff... Not a big deal at all.

 

2012-10-04_21-06-04_612.jpg

 

 

 

Another thing to note is that the case is within 1/8" as thick as the stock R200 case. However, since the R200 case mounts to the mustache bar, the R200 sits further back. I will have to wait until I get a diff in my hands to see how much of an issue that will be - same with the height. I'd guess that I will have to section the frame a little bit to get clearance above the diff.

 

It also might be a better bet to go with a cover that would allow you to mount the diff to the mustache bar, instead of through the uprights, with a spacer in between those and the mustache bar, as would have to be done with this setup. I also have visions of a modified upright setup, so that I could still mount the diff to the mustache bar, and be as far back as it needs to be.

 

Heres a super rough 2 minute sketch of what it looks like now (minus frame sectioning of course)

 

2012-10-04_21-59-13_558.jpg

 

And now with a "modified" upright setup. Probably use something like 1" heavy wall tubing. There will of course still be the cross brace in the lower area that I left out of both drawings. This kind of negates any benefit of the explorer cover,but its a thought.

 

2012-10-04_22-05-05_85.jpg

 

What do you think? I'm open to other ideas here as well. I'll know LOTS more once I pick up a diff and can see how the axles align (front back, up down), and then I'll be able to make some better decisions.

 

This cover might be better suited.

 

211_8_8IRS_Cobra_Mustang_Super_Coupe_Rear_Differential_Cover_Girdle.png

Edited by SUNNY Z

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Your idea of modifying the "uprights" to allow the differential cover to engage the mustache bar (via spacers of suitable shape) is a good one. But I'd worry about retaining (and ideally, improving) the strength of those "uprights" - something not yet attained in your second sketch.

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Your idea of modifying the "uprights" to allow the differential cover to engage the mustache bar (via spacers of suitable shape) is a good one. But I'd worry about retaining (and ideally, improving) the strength of those "uprights" - something not yet attained in your second sketch.

 

As I said, thats just what I got from looking at it for 10 minutes in the garage last night. I'm scheming a lot of different ideas right now. One of which includes leaving the uprights untouched, and welding a mounting apparatus to the mustache bar to accomodate a cobra style cover..... idk yet.

Edited by SUNNY Z

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