How to make the FC Subframe swap WORK
Savanna Rx-7
Joined: Jun 2004
Posts: 1,577
Likes: 12
From: yokosuka japan
options for FC front crossmember swap.
When I built mine in 2004 I ran new frame support tubes through the frame like one of the above guys did, and centered the wheels, use the FC dash and all electronics including a/c etc. running staggered 17 x 9 and 16 x 9 wheels I clear a set of 310 mm rotors with custom calipers with no issues. I used a set of bilstein struts with 1' lowering springs when I mocked the car up and then swapped to coil overs after the first run at the track. ended up with 8kg springs in the front with 4kg in the rear stock roll bar in the back and an adjustable roll bar in the front. A little tinkering and its been good to go ever since. never had any issues with the roll center as when it was all finished the front suspension's lower arms were parallel to the ground. With the rear suspension lowered by 2" with button style bump stops and heim joint lower links to stop the diff from rotating up and have the drive shaft smacking the trans tunnel (upper arms are stock). the overall feel was different from stock FB or FC but not as bad as I had been worried about. still has the snap over steer if you fully compress the rear suspension until it bottoms but with a solid rear axles not much can be done except with either a tri link setup or a complete rear cross member swap (Miata rear sub-frame and diff) .
my originl build thread (low on details high on shenanigans) https://www.rx7club.com/1st-generati...-there-554678/
miata IRS swap thread : https://www.rx7club.com/1st-generati...d-pics-361918/
fc roll center fixes while in the fc read for ideas for the FB. (look at EProdRx7's comments) https://www.rx7club.com/race-car-tech-103/front-roll-center-correction-lowered-fc-760668/
my originl build thread (low on details high on shenanigans) https://www.rx7club.com/1st-generati...-there-554678/
miata IRS swap thread : https://www.rx7club.com/1st-generati...d-pics-361918/
fc roll center fixes while in the fc read for ideas for the FB. (look at EProdRx7's comments) https://www.rx7club.com/race-car-tech-103/front-roll-center-correction-lowered-fc-760668/
Savanna Rx-7
Joined: Jun 2004
Posts: 1,577
Likes: 12
From: yokosuka japan
I haven't noticed bump steer issues, although toe definitely needs to be reset every time ride height is changed, unlike with the stock frontend.
My estimation is that front spring rates need to be increased by roughly 30% to get the same feel, at stock-ish ride heights. The lower you go, the greater this percentage, since the shorter FC control arms make the roll center drop proportionally faster. And there's no option to space the ball joint down like there is with the SA/FB suspension.
My estimation is that front spring rates need to be increased by roughly 30% to get the same feel, at stock-ish ride heights. The lower you go, the greater this percentage, since the shorter FC control arms make the roll center drop proportionally faster. And there's no option to space the ball joint down like there is with the SA/FB suspension.
Newbie
Joined: Jul 2018
Posts: 3
Likes: 0
From: Washington
Considering that the FC subframe can be mounted either by using the front stud hole locations as they are (lengthening the wheelbase) or by relocating the mounting points so that the subframe is mounted rearward 1" (wheels centered in the wheel well), this also effects where the engine is mounted in the car since the engine is now mounted to the subframe.
Question is how does this effect the transmission mount location? Does the transmission mount line up with the cross member as normal with the FC subframe set back 1"?
Also does the engine sit higher or lower in the car assuming the FC subframe is installed the conventional way using a 3/4" spacer at the rear to level the control arms? A change in engine height would effect the yoke and pinion angle.
Question is how does this effect the transmission mount location? Does the transmission mount line up with the cross member as normal with the FC subframe set back 1"?
Also does the engine sit higher or lower in the car assuming the FC subframe is installed the conventional way using a 3/4" spacer at the rear to level the control arms? A change in engine height would effect the yoke and pinion angle.
Banned. I got OWNED!!!
Joined: Aug 2012
Posts: 1,666
Likes: 88
From: San Jose, CA
Considering that the FC subframe can be mounted either by using the front stud hole locations as they are (lengthening the wheelbase) or by relocating the mounting points so that the subframe is mounted rearward 1" (wheels centered in the wheel well), this also effects where the engine is mounted in the car since the engine is now mounted to the subframe.
Question is how does this effect the transmission mount location? Does the transmission mount line up with the cross member as normal with the FC subframe set back 1"?
Also does the engine sit higher or lower in the car assuming the FC subframe is installed the conventional way using a 3/4" spacer at the rear to level the control arms? A change in engine height would effect the yoke and pinion angle.
Question is how does this effect the transmission mount location? Does the transmission mount line up with the cross member as normal with the FC subframe set back 1"?
Also does the engine sit higher or lower in the car assuming the FC subframe is installed the conventional way using a 3/4" spacer at the rear to level the control arms? A change in engine height would effect the yoke and pinion angle.
For a drift setup, you can reduce caster massively and center the wheel in the wheel well by mounting at the factory front stud location and using the LCA and top hat to shift the wheel rearward. Really flattens the tire out at full lock vs. having a large camber change due to jacking.
Old [Sch|F]ool
Joined: May 2001
Posts: 12,880
Likes: 577
From: Cleveland, Ohio, USA
FWIW, I am probably going to flip the knuckles side to side and go back to FB suspension, keeping the FC uprights. This wil make engine mounting much simpler as well as unbork the handling problems.
There are certain Mazda3 ball joints that press in to FB arms but clamp in to the knuckle.
There are certain Mazda3 ball joints that press in to FB arms but clamp in to the knuckle.
Reviving this kinda old thread...
I'm working on this right now and am worried I'm not lining up the subframe correctly (my goal is to keep the wheels in the center of the fender). How far back do I need to move it? I've read 1" but my measurements show nearly 2" as best I can tell eyeballing the control arms with a straightedge between the fender sides. Anyone know the exact amount?
I'm working on this right now and am worried I'm not lining up the subframe correctly (my goal is to keep the wheels in the center of the fender). How far back do I need to move it? I've read 1" but my measurements show nearly 2" as best I can tell eyeballing the control arms with a straightedge between the fender sides. Anyone know the exact amount?
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sen2two
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Jul 22, 2011 03:06 PM