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Discussion Starter #1
OK, I have a decision to make here and need your input. I have two IRS pumpkins, one iron and one aluminum. Both have 3.27 gears, a T-Lok, 28-spline, and both are in great shape. The iron case is out of a '89 Super Coupe, the aluminum is out of a '99 Cobra (I think). The motor is a 427SO w/ approx. 475-500HP and about the same in torque. Which case should I run? Thanks for your help, have a good one.

-SGC :D
 

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I'd use the aluminum one because it sounds like it's new. Last weekend I drove a 392 stroker powered, aluminum IRS car on slicks for for 10 laps at Willow Springs and my last concern was breaking the IRS. The lack of a front sway bar was very concerning.

Roger
 

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The alum is nice because it's a little lighter. But I thin k you're giving away some strength. I used a cast iron unit and solid front mounts in an attempt to make it last longer.

Don't want this to happen.


But read this thread: Differential Brace
 

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Discussion Starter #4
Thanks for the info guys. OK, heres the tally so far:

Aluminum Case - 1
Iron Case - 1

Anyone else? Thanks again!

-SGC
 

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The damage shown in boB's picture was the rear cover on the pumpkin. Both versions (aluminum and iron) use rear covers made of aluminum.

If you have both, use the aluminum and save some weight.
 

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The damage you see above most likely was caused by having a solid rear mount with rubber front mounts. Use VPM's solid aluminum front mounts with the aluminum case and never give it another thought.
 

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The damage shown was not on a cobra. Both rubber mounts. It looks like it lost its left axle as well.
 

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Shawn,

The photo opinion of a wrecked 7.5 T-bird IRS pure bs. I have two cast iron SuperCoupe center sections sitting here and they both have an 8.8 clearly cast on top.

Roger
 

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The photo shown IS a Cobra, a 2003 SVT Cobra that is.
This happened while at the Dragstrip and this is why the 03 Cobra guys are doing the Solid axle swap. To me the 03 Cobra is a Roadracing car with its IRS setup not a Drag car. as many stated the problem lays on the rubber stock mounts, too weak they flex a lot putting strain on the case and cover, altought it is probably not required I installed a brace to prevent this on project SC:


 

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Shawn,
Since you have a 1 to 1 tie, I'll break the tie. Use the cast one and send me the aluminum one for my little 302 :D
 

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I've never read of this happening to any FFR either aluminum, or iron. I feel that there is no way we could hook enough power to the ground to have this happen - so use the aluminum one and save a little weight (which is always a good thing)!
 

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I was talking with Carl Wade yesterday about this issue. We were standing there looking at this beautifull Superformance Cobra with a 502 Ford crate motor, 8 stack EFI, Tremec 5 speed, and 15" BFG Eagle II tires. Superformance uses the same 8.8 center section we do. That particular car is now on it's third center section.

The entire diff seems to fall apart. Like the case can't carry the load placed on the bearings. The weak link in traction is the tires, of course. But the instant shock load is just too much. Ford only rates these at 210 ft/lb.

I think the big differance is that they are rubber mounted in the front, and solid mounted in the rear.
 

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boB, did he break them at the drags, or on the street? I think if there is a weakness in the aluminum housings, it it due to a greater rate of thermal expansion than the iron version. This probably causes the setup tolerances to change enough to tear things up under the right circumstances (like the torque of that 502 applied all at once!) I think in those situations, a stout solid axle might be a better choice. This is why the hardcore drag racers swap the rears on the IRS Mustangs. For most of us, though, the aluminum will be a good choice.

Brian
 

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Ok, am I missing something here? Even if you are concerned about breaking the diff, aluminum or iron pumpkin wont make a difference. Like DougR said, both use an aluminum rear cover. And thats the piece that breaks, not the housing itself.

If you really wanted to take some overkill precaution, Sergio has the only solution (IMHO!).

That being said, I am using the aluminum diff with solid aluminum mounts in the front. As long as I dont hear about ANYONE ever having broken one, thats enough for me.

Lukas
 

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Discussion Starter #17
Thanks for all the input. It looks like the general consensus is to run the aluminum case, solid bushings in the front and just run it. Sounds good, but I would like to throw one more thought into the equation. Would the added weight of the iron case have any benifit in handling since I am running a big block? Thanks!

-SGC
 

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I have the aluminum one with a 427 and sticky goodyear race tires so far no issues but i have a lot of respect for whats under the hood, i think the handling issue is a moot point Bob
 

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Originally posted by B+L FFR 1686:
boB, did he break them at the drags, or on the street?
Strictly street driving.
 

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Discussion Starter #20
Thanks for all the info guys! Got my work cut out for me. Have a good one.

-SGC
 
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