Is it true you can put the new 2003 Mustang Cobra 8.8" rear end in the FD? I'v heard about it, i just wanted to know what it wouls take to do this?

you can, but it requires modification... and its only good for drag racing..



the stock FD rear end can handle just about anything you throw at it.. most of the LS1 FD guys go with the cobra rear end... but a friend of mine with Turbo Nitrous LS1 is going with a TII diff.

Why do you say that? Its an independent rear diff, similar to the FD one, just stronger. The suspension wont change, only the diff, axles and driveshaft.



But it is nowhere near a bolt in, you have to fab the mounts for the diff, and get custom axles and driveshaft made.



Jimlab from RX7club did it, you can go over there and do a search for his name and youll find the info on it.

i say its mainly for drag racing because that is why people want to swap it out.. its a stronger IRS setup.. yet its no where near as light or as good as the original FD's setup.. I'm sure the engineers at Mazda have a little bit more working knowledge in physics than us. https://www.nopistons.com/forums/pub...IR#>/smile.png

you need a whole new subframe. how about a little more research before posting

i think the cobra rear in is accually lighter then the mazda but i'm not sure.

ok so baiscly it's not a good idea, looks like id be better off just bracing the stock FD one and putting a Kazaa LSD in it.

exactly what I'm doing.

Actually, despite a significant increase in the size and strength of the parts involved, the aluminum '03+ Cobra 8.8" IRS differential assembly is about 7 pounds lighter than the cast iron original.



And, while you're on a roll, most people don't want one for drag racing. They want one to retain the handling the car came with while improving strength, decreasing weight a little, and getting a wide range of gear ratios in the bargain.



FD 36 lb. cast iron housing on the left, Cobra 14 lb. aluminum housing on the right.

http://www.rx7club.com/forum/attachment.ph...&postid=1380794



Cobra 8.8" ring and pinion on the left, FD 8.0" (203mm) ring and pinion on the right.

http://www.rx7club.com/forum/attachment.ph...&postid=1391549



FD Torsen on the left, Cobra 8.8" Zexel Torsen on the right.

http://www.rx7club.com/forum/attachment.ph...&postid=1423200



FD on the bottom, Cobra 8.8" on top.

http://www.rx7club.com/forum/attachment.ph...&postid=1423203



Cobra 8.8" differential, cradle, and FD rear subframe.

http://www.rx7club.com/attachment.php?s=&postid=2585932



And one more...

http://www.rx7club.com/attachment.php?s=&postid=2585938



Any questions?

yeh why does the RX7 club logo come up and its says unauthorized link?

Contact Ryan.I cant see ****.

Yeah bad links.

FYI Jim, you can't cross link pix between the forums. Luckily posting images here at nopistons doesn't take 30 min like some places. You can attach them directly to your post if you want us to see them.

I checked the links and they work for me. Maybe you have to have an active account on RX-7 Club forum. In any event, here are the pictures I mentioned above.



FD 36 lb. cast iron housing on the left, Cobra 14 lb. aluminum housing on the right.

Cobra 8.8" ring and pinion on the left, FD 8.0" (203mm) ring and pinion on the right.

FD Torsen on the left, Cobra 8.8" Zexel Torsen on the right.

FD on the bottom, Cobra 8.8" on top.

Cobra 8.8" differential, cradle, and FD rear subframe.

Last one...

Jim when we clicked the link we saw this.

That is one beefy looking ass end. Did you do the welding or did you source that stuff out to someone?

Oops, not done yet. Here's the 8.8" setup in my car...

And finally, the hybrid axle I made for test fitting and finding the proper center shaft length.



The first pair of 300M chromemoly hybrid axles are being made right now, and there are four people waiting for copies of my Cobra IRS cradle.

I have a MIG welder, but I'm no expert. I have all my final fabrication and TIG welding done by a friend who builds custom show cars for a living. I just fabricate welding jigs or machine pieces like the steering rack brackets for the engine cradle to help out.



An example of my welding... https://www.nopistons.com/forums/pub...IR#>/smile.png

nice work man https://www.nopistons.com/forums/pub...>/bigthumb.gif

It's no row of nickels but it'll work. https://www.nopistons.com/forums/pub...IR#>/bigok.gif

Seriously thats not bad for MIG welding.

Thanks. https://www.nopistons.com/forums/pub...IR#>/smile.png



I milled out the center of the Cobra end to the diameter of the FD axle, then used a chop saw to cut the FD axle down to the length with about 2" of free play to slide it in or out as needed. I drilled and tapped three holes in a "Y" configuration in the Cobra portion and used 14mm bolts to hold the FD axle in place temporarily while I got the fitment right (see below). Then I welded it in place to make it permanent, but it was never intended to be used for anything but measuring the overall length for the new center shafts.



The production axles won't neck up to the large diameter of the center of the Cobra axles, because it's just extra weight and doesn't add any strength. They'll be a single diameter from end to end and come with new CV boots for the Cobra end that fit the smaller diameter axle. I was quoted $600 for everything, including grease, which is $250+ less than RP's 300M axles.

So you mocked up the entire rear end only to ship it out and have someone else make the final product? https://www.nopistons.com/forums/pub...1047683894.gif

Again, thats well executed.

I 2nd that motion.

damn that's sick. if only you could just drop it in.

So what's the final cost of the conversion?

And what are your driving impressions of it? How much was the cobra rear end? Reason I ask is I would like to do this is my FC.

Anyone know anything about dropping a Tii rear end in a Fd ?

I have a T2 LSD you just put it into the FD case with the FD ring and pinion. Suppose to be better for drag. It's just stronger.

So nothing more than just swapping the parts out?

Thanks

you might have to re shim it.

Where do you knuckleheads get your information from?

damn yo, dont just say it aint so, say what is so... https://www.nopistons.com/forums/pub...IR#>/dunno.gif

I'm sure he would love nothing more then to know how this rear end handles or how the car runs over all. Its been a bit

What, Jims car isnt on the road yet? https://www.nopistons.com/forums/pub...1047683664.gif

$550 for the cradle, $600 for the 300M center shafts with boots, clamps, and grease for the Cobra ends. $100-150 for a pair of used '03+ Cobra axles. (Unfortunately, you can't buy the inner CV separately) I've seen '03+ Cobra 8.8" IRS differentials go for $300-400. Replace the boots on the FD outer CV joints and you're looking at about $70 ea. for boots, clamps, and grease. Other than that, your driveline will have to be modified and if you still have a rotary, you'll need a transmission brace because the PPF is eliminated. Depending on what you can do for yourself and what kind of deals you find, maybe $1,500-1,600 for the conversion.