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FB rear suspension locations 12A, 13B?

Old 01-20-11, 08:12 PM
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FB rear suspension locations 12A, 13B?

Well with the new radial tires available I'm thinking about building a narrow body car for EP. I'm leaning toward an FB with a 13B because I have a bunch of stuff to fit one and I have a ton of experience with the chassis(I was business partners with Jim Susko when he was first developing his suspension set up back in the early 90's)

It's been many years since I built an FB for IT and I need a little help remembering something. I seem to recall the GSL SE chassis' had slightly different chassis mounting points for the lower control arms in the rear and the cheater set up in ITS was a 13B in a 12A chassis.

Anybody have any idea if I'm losing it or if this is true?
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Old 01-20-11, 08:29 PM
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I think the cheat your thinking of is the FC front subrame in the FB.
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Old 01-20-11, 08:49 PM
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lol
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Old 01-20-11, 10:39 PM
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you're right but its all the 84-85's. they lowered the front of the rear lower trailing link, i think 10mm.
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Old 01-20-11, 10:44 PM
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Yes, in '84 they went all FUBAR on the rear geometry to increase roll understeer, on all cars not just GSL-SE. Both of the Series 3s that I've had were originally 12A cars and they had the lowered chassis mounting point.

GSL-SE also had fewer clutches in the limited slip compared to a 12A car, not sure if this even matters in EP.
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Old 01-20-11, 11:24 PM
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The trailing arm mount on the chassis is 19mm(3/4") different on the 84-85 chassis
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Old 01-21-11, 12:03 AM
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So it looks like an 81-83 chassis is the best one to look for. OK, a rust free, non sunroof, 81-83 RX7.... that shouldn't be too hard to find...lol
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Old 01-21-11, 06:51 AM
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A friend of mine found a rust free non-sunroof '79.

IMO the '79-80 is a much nicer chassis, somehow they just seem a whole lot lighter. But then, you'd be cutting one up to turn into a race car, so use a '81-83.
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Old 01-21-11, 07:35 AM
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Originally Posted by jgrewe View Post
So it looks like an 81-83 chassis is the best one to look for. OK, a rust free, non sunroof, 81-83 RX7.... that shouldn't be too hard to find...lol
I have a 81 GS chassis with a LSD and rear disc brake conversion. RE-speed bushings. 12A car, new stock radiator etc. It is currently torn down for a complete re-paint/resto due to a enginebay fire. I am pretty reasonable on the price if you would like to PM me. I also have the original drum brake, non-LSD rear end if you needed it for IT purposes.

I am in Denver, NC just so you know a location for transport purposes.

Dave
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Old 01-21-11, 08:19 AM
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How reasonable? (Not to cut out jgrewe, but interested)
And how close are you to Mooreseville/Charlotte? I need to drop in on some freinds there anyway.

I have an S4 FC chassis here to cut up into an EP car, but I still feel like doing an early car at some point.
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Old 01-21-11, 09:12 AM
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Is this Derek that used to have a MB FD?

Anyhow, I am on the west side of Lake Norman. 10 miles from Mooresville and 30 from Charlotte. PM me for more info. Pretty reasonable I don't want to threadjack.

Dave
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Old 01-21-11, 07:38 PM
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I already have most of the running gear, I'm just looking for a shell to build an E Production car that is designed for radial slicks from the start. I've seen them on CList in the past close to me in the St Petersburg area, just wasn't in the market until I saw how these new tires are performing.

I think the earlier 79-80 chassis' are a little heavier than the 81 to 83's. Its only a few pounds but at a certain point each pound gets pretty expensive to lose. I could be wrong, last time I built one I was using a 28.8K modem to dial up CompuServe if that gives some of you a clue. I do remember the power window doors were lighter than the manual crank ones for an IT car. when we had to have all that crap in the car still.
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Old 01-21-11, 07:50 PM
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79-80 chassis are lighter, if your not counting the bumpers. Especially if it's a non-sunroof car.

The 79-80 bumpers are much lighter. If you swap on the later bumpers to a 79-80 chassis, It will be the lightest starting point.
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Old 01-22-11, 03:24 PM
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if i'm not mistaken, JGrewe is correct. i think the '81-'83 (Series 2) non-sunroof, base models were "officially" about 40 pounds lighter than the Series 1 (SAs) were.
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Old 01-22-11, 11:45 PM
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Originally Posted by diabolical1 View Post
if i'm not mistaken, JGrewe is correct. i think the '81-'83 (Series 2) non-sunroof, base models were "officially" about 40 pounds lighter than the Series 1 (SAs) were.
yeah its more like 80. my 83 LE was 2330lbs with a full tank and the SA was something like 2480. of course the SA has the nuclear reactor weight penalty, but even still the SA is a little more
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Old 01-23-11, 05:49 AM
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yeah, i have a book at home, and if i recall, it had the Series 1 base cars somewhere over 2350 and the Series 2 base cars just over 2300 pounds. i just remember being quite surprised when i first read it, because like some many other people, i assumed the SA was the lightest. i honestly don't recall the actual figures, but i guess it doesn't really matter at this point.
Originally Posted by j9fd3s View Post
... the SA has the nuclear reactor weight penalty, ....
i like that ... and, yes, those bloody things are heavy.
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Old 01-23-11, 09:30 AM
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Damn, that means I'm two for two on remembering **** correctly! Well, I give myself half credit for the suspension, I didn't know it was all later cars.

A friend of mine has an 84 12A car with no sunroof that he would probably give me, I'm thinking I could just change the rear control arm pick up point with a part from an earlier car.

Can the SA's reactor be put in a later chassis?
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Old 01-23-11, 11:53 AM
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No reason why not, although if you don't use an air pump it will melt down.

For what it's worth - my '85 weighed 200lb more than my '80, both with the same amount of interior and the same exhaust system. And the '80 still had functional air conditioning. 2210lb versus 2400lb, as measured by the scales at Norwalk. If the FB bumpers are indeed lighter than the SA bumpers, then Mazda must have added a lot of sheetmetal to the shells. I can't see the rearend being 200lb heavier than the SA unit.

Also FWIW - Both cars were 100lb nose heavy with my top-heavy lanky *** sitting in the car.
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Old 01-23-11, 12:05 PM
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you don't even have to weigh the bumper to see the difference. Pick one up and you will notice right away.


SA body with FB bumpers will be the lightest factory combo.
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Old 01-23-11, 01:43 PM
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Originally Posted by peejay View Post
No reason why not, although if you don't use an air pump it will melt down.

For what it's worth - my '85 weighed 200lb more than my '80, both with the same amount of interior and the same exhaust system. And the '80 still had functional air conditioning. 2210lb versus 2400lb, as measured by the scales at Norwalk. If the FB bumpers are indeed lighter than the SA bumpers, then Mazda must have added a lot of sheetmetal to the shells. I can't see the rearend being 200lb heavier than the SA unit.

Also FWIW - Both cars were 100lb nose heavy with my top-heavy lanky *** sitting in the car.
the 81-83 cars seem to be pretty light too. my friend has a CSP prepped 81 that's 2250lbs. and since CSP concourses (to be race legal he had to replace the A pillar trim...) with a full interior, the only thing that's removed is the stock exhaust and the AC.

i think my black GSL-SE was 2540! manual steering and AC
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Old 01-23-11, 01:48 PM
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Originally Posted by jgrewe View Post
.

A friend of mine has an 84 12A car with no sunroof that he would probably give me, I'm thinking I could just change the rear control arm pick up point with a part from an earlier car.

Can the SA's reactor be put in a later chassis?
https://www.rx7club.com/showpost.php...&postcount=112

i looks like there is room to move it back up, you just need some mad fab skillz
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Old 01-23-11, 05:25 PM
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I was thinking of a reactor like a flux capacitor with a Mr. Fusion upgrade, not an emission unit. Hoping there was some secret power to be had...

j9fd3s, I was thinking of drilling out the spot welds on that whole chassis mount in the pictures in that link. I wouldn't be allowed to just drill some new holes and move the control arm up unfortunately. Replacing that whole mount would be easy.
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Old 01-23-11, 10:49 PM
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The Prod rules allow you to fix the geometry issue at the rear axle if you are creative. So the model year you start with isn't relative in my opinion. Regarding weight - yeah starting with the lightest car is important but I have seen EP cars that built from all SA/FB model years that easily make weight and have to be balasted.

This is shot of an EP rear suspension built by KC Raceware. Give Charlie a call, he can explain the 4 traction bar setup they are using. www.kcraceware.com



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Old 01-24-11, 08:36 AM
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I was looking at the rules for the wording on whether or not you can move where links attach to the rear end housing, that would make the chassis end a non-issue. Can you point to the line in the GCR that opens that door?

I understand the 'traction bar' option I just don't think I would go with a 4 link like the KC set up. I like the looks of the support inside but I recall computer modeling showed a three link had fewer issues with roll steer and binding with the short links these cars have.
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Old 01-24-11, 08:50 AM
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I would think a 3-link and Watts link would really be the way to go on an early car, but I am very likely behind the curve on solid axle stuff.
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