FC Rearend in a FB
 

Has anyone attempted to put a FC Rear subframe in a FB???

No. Not possible w/o a mountain of $$ and skills. Not worth it.

Thats a closed minded reply. Of course its never been "succesfully" done. But has anyone ever tried? What was their wall? why couldnt it be completed? Answers to these questions may or may not show it can't be done.

miata rear would be a better choice.....posssible.... time and money

its deffinatly doable imho but skills would be imperitive would probably be easier to not use the full subframe and fabricate alot of it yourself

mounting the diff itself wouldnt be that difficult (i dont think) it would be the suspension and hub assembly that would pose the most threat to failure

It's not a closed minded approach. It's not worth it.

https://www.rx7club.com/showthread.p...&highlight=IRS

There were mazda test cars with fc rear ends, and a forum member swapped the miata rear a few years ago. A local here had the FC rear stuffed under an FB with marginal success (read half assed).

It really all depends on how much time/money you want to sink into it. If you are determined to have IRS in your FB, don't use the FC bits, opt for something a little more modern with better handling options.

miata swap= https://www.rx7club.com/showthread.p...light=irs+swap



FD bits (i know nothing else about this car)

http://rx-7.org/gallery/1stgen/image...ionyellow7.jpg

I got a few pics of Miata subframe in a 1st gen. I planned on putting a t2 rear in a 79 a while ago... Maybe ill do it in the future still.

It's really not all that hard if you can weld and measure.

WOW!! The miata subframe swap looks MUCH easier... As of right now I have a FC Subframe. I can measure, Cut, Weld, And i'm thinking about attempting to put it in my FB.

Just an honest question. Why would you want to swap it? The FB rear end is actually pretty awesome lol. Its a LOT lighter assembly, and the watts link is a pretty good rear end suspension set up.

I want more options. I have a FC that Im tearning down and Im swaping the FC front subframe into my FB.. I plan on running a set of coilovers, and I would love to run the other pair in the rear. But most of all the IRS.

That and I like projects..

You can cut, weld, and fabricate with metal - Anything is possible.

http://www.offroaders.com/readers/od.../4x4--rx-7.jpg

For all the time and work it'd take, why not just fab a proper race-spec rear end? It's not like the FC rear "almost" even fits or is even really very good. You're essentially starting from scratch.

Even if you succeed
 

Even if you succeed, you're still stuck with the passive 4 wheel steering. Mazdatrix sells bushings that eliminate this problem.

When I was at the salvage yard yesterday, I noticed a complete FC rear end on the ground next to the car and yes, the thought of putting it in my FB made me look closer. I didn't see any easy way to do it in my five minute quick check.

The front FC cross member and rear subframe were first tested by Mazda on 3 FB engineering test mule cars for track testing. 8 color pictures of test mules and details on suspension installation.
FB vehicle designation X-0, X-1 and X-2
See pages 121-123 RX-7: The New Mazda RX-7 and Mazda Rotary Engine Sports Cars (February 1986)
Jack K. Yamaguchi (Author)
ISBN-13: 978-0312694562

[QUOTE=rx7lives;10971084]Even if you succeed, you're still stuck with the passive 4 wheel steering. Mazdatrix sells bushings that eliminate this problem.

How am I "stuck" with the 4 wheel steering if Mazdatrix sales bushings to eliminate the problem???

The Miata rear suspension is a better piece. If you want to do an IRS that is the better direction. Doing an FC or a Miata rear suspension swap is going to involve allot of fabrication so might as well start with a better part.

I wonder how hard it would be to get a miata subframe??? I live in a po dunk town.. Portland oregon is 80 miles away, But all the u pull it places there say I cant take subframes off!!! (Saftey hazard)

What kind of crap is that?

Go with the FC subframe for one main, but very crucial reason...

The Miata rear is not any stronger than the 1st gen rear. They are both 7" ring gears. If you go with the FC sub-frame, you can always get a TII rear for it which is a very proven stout rear.

They are also much easier to get a hold of and most likely cheaper.

If I was doing an irs swap with factory parts I would think hard about R180 subaru STI stuff, or late model toyota cressida/supra stuff.

Cost is the biggest issue for me.. I blew up another turbo motor so...
I bought a 88 RX-7 For $900 It has a good running N/A engine, And has the 5 lug hubs 4 piston front breaks and a LSD.

I thought I would do the FC subframe swap and throw the N/A 13B in there untill i build my next turbo 4 port.
So now Im left with a fc rearend that allready has 5 lugs and a good working LSD.

The fabrication seems like the cheap part.. I have all the tools and the time to do it. What I dont have is cash to drop on a miata rearend or a STI rearend...

Plus I am buying a set of Ksport coilovers to put on the front, And it would be vary cost effective to use the rear ones as well.. If i put a miata rearend in the car then I would have to buy another set of miata coilovers just for the rear..

Can anyone tell me what the differences between my rearend and a Turbo II rearend???

The important difference is the ring gear size. 7" for NA, 8" for TII... PLus the axles are thicker on TII's. Also has more stout stub shafts. Just an all around better option. And lucky enough, its a direct bolt in swap for the NA rears in the subframe, which are identical.

Bigger is better here.

As is the same for solid domestic rears. Ford 9inch is stronger than an 8.8. Which is stronger than the ford 8inch. ect. ect...

the T2 diff and the miata diff ears are the same, so you can put a T2 diff right into a miata....

IMO, the miata suspension is better, and it would fit the FB more easily

the FC suspension isn't that great, especially for drag racing, and doesn't fit the FB very well, so its a lot of work, for questionable gain....

Good to know! Thanks for the info.. Im going to have to do some research on ratios now..

Questionable gain.... ??

I dont drag race the car.. (well like once a year) so it seems like a hands down upgrade/gain to me...(IMO) That and I think I can make the subframe fit for less then $100. metal, cut off discs and welding wire doesnt cost that much..

AS an FC guy, I would say it's not really worth it. For the time and effort to cut fab and weld, I would look into an 8.8 IRS install.

Back when I had my 82 rx-7 and my 97 t-bird I did a bit of measuring. I think the IRS out of the V8 powered t-bird or cougar would fit under an FB just as well as an FC unit. The width of the rear end is about the same as a solid axle mustang, meaning you can probably fit it with FWD offset wheels under the stock fenders. The V8 powered t-bird and cougar also came with an LSD equiped 8.8 diff, so your set there. More or less the same setup that came under the SVT cobra in the early 2000's but can be had from just about any junkyard. Be careful though, the v6 powered cars came with the 7.5 diff, much weaker but would probably still withstand a stock TII engine, though no LSD.

when the stock live axle can be made to pull ~1.2G in the skidpad, yeah it's a questionable gain.

Sounds like I need to do My homework!

Sounds like I need to do my homework too. I was struggling with this same issue. I have been considering the same situation and trying to decide if its worth the work. However, if the stock unit can be modded to that kind of results that seems like the way to go...

For those who didn't see his thread, he actually did go through with this swap here:

https://www.rx7club.com/build-thread...end-fb-998272/

He hasn't been on in months though so i'm not sure how it actually worked out when/if he got the car back on the road and running. Encouraging to know that it can actually be made to fit though..

you need to swap the entire sub frame as far as ive heard but its very plausible. you can also swap the entire front subframe as well. from what ive been told. but i could be wrong.

lets see bigger bolt pattern , brakes, suspension options, LSD all in one swoop.... somehow not worth it? :scratch:


ive gotten rollers before for free with turbo drivetrains in them. swap over call it a day. :icon_tup:

I have the FC front end, it's kind of a upgrade and a downgrade. You get more suspension options but you get worse suspension geometry unless you do some serious surgery to the body channel. Call it a wash.

Trailing arm suspension, however, is an answer to a question that shouldn't have been asked, namely "How can we make an IRS that sucks in every way possible?" Mazda did all of the funky links and squishy bushings in an attempt to alleviate some of a trailing arm suspension's more interesting handling quirks, but in the end you still end up with a suspension that you can't really put power down with.

Here's me carrying a front tire at a corner exit. A 3-link works, on any kind of surface. L/R is near full compression, R/R is drooping and still able to grip.

http://mtbshred.com/copper/albums/ft...l_IMGP8724.JPG

PS - Note the fender gap at the top of the door vs. the bottom - my car's getting a bit banana shaped :) Time for another one probably.

there was a guy on here that did and show lots of pic of what he did

Yeah I posted the link above ^^

Too bad he hasn't been back on to comment on how it's working out...

Am just in the process of doing this swap myself can you elaborate on the downsides of worse geometry? Looked like you pick up a bit of castor to me which can't be a bad thing and widen the front track. Would be interested to know the downsides so I can try to engineer them out a bit.

The front track doesn't get widened. You still end up with positive camber just like an FB, too.

There's little you can do about the worse geometry. I've seen people notch the body rail a few cm to get the subframe higher up in the body, but you're still stuck with control arms that are a lot shorter so rollcenter moves around a lot more.