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FC Double A-Arm Conversion

Old 03-29-13, 01:17 AM
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FC Double A-Arm Conversion

Converting an FC to A-Arm suspension for F Prepared Autox. I've Attached the current mockup, current goal is -3.0 static with a camber gain of -1.0 per inch(comments welcome). I did a lot of googling and outside of the Locost community this hasn't been documented to my knowledge, so here ya go. Not a ton done yet, but it's accelerating. All Fabrication is courtesy of Frank Adams.

As an aside. I have a complete ISC Bilstein Coilover setup for sale as a result of the suspension change, pm/email for details. I bought functional camber plates for the kit instead of the shock shaft bending original design---
Attached Thumbnails FC Double A-Arm Conversion-rx7-upright.jpg  
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Old 03-29-13, 03:21 AM
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Originally Posted by ChopsMcgraw View Post
Converting an FC to A-Arm suspension for F Prepared Autox. I've Attached the current mockup, current goal is -3.0 static with a camber gain of -1.0 per inch(comments welcome). I did a lot of googling and outside of the Locost community this hasn't been documented to my knowledge, so here ya go. Not a ton done yet, but it's accelerating. All Fabrication is courtesy of Frank Adams.

As an aside. I have a complete ISC Bilstein Coilover setup for sale as a result of the suspension change, pm/email for details. I bought functional camber plates for the kit instead of the shock shaft bending original design---
Very cool set up

cant wait to see finish result !!
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Old 03-29-13, 06:08 AM
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Looks awesome! And the locost clguys ate usually pretty helpful, been thinking about building one for years!
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Old 03-29-13, 04:14 PM
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Contact Tripoint engineering.

They build a FP (maybe EP back then?) FC in the 90s with double wishbones in the front. I'm sure you could ask them about it.

I've never seen any pictures of it though.

awesome project
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Old 03-29-13, 05:39 PM
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its the holy grail! we have looked into it on and off over the years, and the only real "hard" part is that the FC uses the FWD style ball joint, every other RWD Mazda uses a tapered seat ball joint.

so you can't take a spindle say from and Rx8, fab up an upper arm and a couple of brackets and be done!
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Old 03-29-13, 09:00 PM
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S4 control arms have bolt on ball joints so all you would have to do is fabricate a ball joint holder?
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Old 03-29-13, 10:57 PM
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Originally Posted by j9fd3s View Post
its the holy grail! we have looked into it on and off over the years, and the only real "hard" part is that the FC uses the FWD style ball joint, every other RWD Mazda uses a tapered seat ball joint.

so you can't take a spindle say from and Rx8, fab up an upper arm and a couple of brackets and be done!

Yeah, would be awesome to be able to parts bin it, the reason you stated is why we are retaining the stock spindle. Still, I'm amazed at how relatively simple this is appearing, waiting for the other shoe to fall . Currently waiting on a ball joint reamer to move farther, man those are pricey, any one know where to source a cheap one for two time use?
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Old 03-29-13, 11:01 PM
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Originally Posted by Keeble View Post
S4 control arms have bolt on ball joints so all you would have to do is fabricate a ball joint holder?
Lower Ball Joint is bolt on, we used the stock spindle-mcstrut attachments and my buddy fabbed an adapter to utilize a generic circle-track ball joint. We will then do some measuring, bend some tube, do some welding, cut some holes, weld some brackets, and call it done-
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Old 03-30-13, 12:55 PM
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How much does your roll center move with that camber curve?

Thinking about what j9fd3s said... and knowing that the Miata and FC steering racks are the same except for width... I wonder if it'd be practical to get a Miata front suspension, widen the subframe by the difference in widths, use the RX-7 rack, and merge it with the FC nose.

Or tweak the strut geometry to get your desired camber curve. Mostly a factor of moving the strut towers inboard. If you need camber bolts to REDUCE negative camber, you're on the right track.
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Old 03-30-13, 01:19 PM
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Originally Posted by peejay View Post
How much does your roll center move with that camber curve?

Thinking about what j9fd3s said... and knowing that the Miata and FC steering racks are the same except for width... I wonder if it'd be practical to get a Miata front suspension, widen the subframe by the difference in widths, use the RX-7 rack, and merge it with the FC nose.

Or tweak the strut geometry to get your desired camber curve. Mostly a factor of moving the strut towers inboard. If you need camber bolts to REDUCE negative camber, you're on the right track.
well since the FC uses a FWD ball joint that means 626 spindles go right on, use 626 struts, and go 4WD!
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Old 03-31-13, 09:12 PM
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Originally Posted by peejay View Post
How much does your roll center move with that camber curve?

Thinking about what j9fd3s said... and knowing that the Miata and FC steering racks are the same except for width... I wonder if it'd be practical to get a Miata front suspension, widen the subframe by the difference in widths, use the RX-7 rack, and merge it with the FC nose.

Or tweak the strut geometry to get your desired camber curve. Mostly a factor of moving the strut towers inboard. If you need camber bolts to REDUCE negative camber, you're on the right track.

There would be additional penalties for modifications/substitutions of the subframe. If I stuck with the struts I would have just run a ton of static negative camber like I have in the past, but I've dealt with strut cars for the last 6 years and am going to try and eliminate that compromise-
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Old 03-31-13, 09:14 PM
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Upper Control Arm laid out-
Attached Thumbnails FC Double A-Arm Conversion-photo.jpg  
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Old 04-01-13, 10:20 AM
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Looks good!
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Old 04-01-13, 11:11 AM
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A guy I know did this on his v8 FC racecar. Very well done. He replicated the FD geometry as much as possible. Im considering doing something similar.

http://www.norotors.com/index.php?topic=8044.0
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Old 04-01-13, 10:36 PM
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I remember seeing pics of a 510 with double wishbone front based off of FC parts years ago online. Wonder if I can find it again.
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Old 04-01-13, 10:47 PM
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I think it was this car, but the links are down. FC lower arm and spindle with supra alum. upper arm.

Datsun 510 custom 5 lug and rotor conversion
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Old 04-02-13, 01:21 AM
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Originally Posted by designfreak View Post
A guy I know did this on his v8 FC racecar. Very well done. He replicated the FD geometry as much as possible. Im considering doing something similar.

http://www.norotors.com/index.php?topic=8044.0
Cool link, wish I had seen it earlier.

We are just planning on mounting the shock to the lower arm, and a circle-track weld-in balljoint on the uppers.
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Old 04-02-13, 08:39 AM
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Originally Posted by ChopsMcgraw View Post
Cool link, wish I had seen it earlier.

We are just planning on mounting the shock to the lower arm, and a circle-track weld-in balljoint on the uppers.
I like your design a lot better. maybe it's a good thing you didn't see it earlier
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Old 04-03-13, 01:03 AM
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Originally Posted by eage8 View Post
I like your design a lot better. maybe it's a good thing you didn't see it earlier
Thanks, hopefully it's strong enough
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Old 04-03-13, 01:05 AM
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Current Mockup
Attached Thumbnails FC Double A-Arm Conversion-photo-1-.jpg  
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Old 04-03-13, 12:47 PM
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Very nicely done! I am really considering doing this before the chassis is painted We have made the front end tubular, so This will be pretty straight forward.

However I am not a big fan of the lower ball joint that comes with the FC due to lack of adjustment. Are you doing anything in that department? It appears you are using the stock lower ball. I know AWR has a custom one built, but a local guy we know had some issues with it.

It might be easier/better on the long run for me to just buy an upright and build the double a-arms from scratch!
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Old 04-03-13, 03:50 PM
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I just put the balljoint on top of the arm for the time being. If pish comes to shove, we may try to modify a stock one.



Originally Posted by abeomid View Post
Very nicely done! I am really considering doing this before the chassis is painted We have made the front end tubular, so This will be pretty straight forward.

However I am not a big fan of the lower ball joint that comes with the FC due to lack of adjustment. Are you doing anything in that department? It appears you are using the stock lower ball. I know AWR has a custom one built, but a local guy we know had some issues with it.






It might be easier/better on the long run for me to just buy an upright and build the double a-arms from scratch!
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Old 04-03-13, 06:48 PM
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I was telling one of the guys I am working on a tubular lower arms which will mostly likely allow some adjustment for the lower ball joint. Will keep you updated on the progress.
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Old 04-03-13, 07:52 PM
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Glad to see someone else trying this out. I'm doing the same thing, for the same class too!
Curious about the other specs, like roll center migration, caster, scrub, steering axis inclination etc. You don't have to give away ALL your secrets, but just wondering how you settled on the setup/dimensions that you did.
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Old 04-03-13, 11:08 PM
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looks like the upper arm is longer than lower? that seems unlikely to have any kinda of decent camber gain unless you run a subterranean roll center
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