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I'm looking for some pointers or leads to hopefully get my project rolling again... I've got too much sentimental value and time invested into the car to scrap it (You can't scrap rust free!) but I sure am sick and tired of having a bare shell and parts EVERYWHERE in the garage. I've explained my plan below and am curious what people have to recommend for spring/damper setups. What people think of the handling "benefits" for a lack of better words when it comes to the swap, and if it's even worthwhile to pursue. Keep in mind my sole reasons for wanting to do this swap are rack and pinion steering and bigger brakes.
First and foremost let me say I've been trying to do as much research as possible on the subject before I even make another dead end thread regarding the FC subframe swap. So for those who are not familiar, Do yourself a favor and start searching the following usernames for information:
I've found these names worthwhile to mention for one reason or another. Unfortunately some of these users are no longer active and I can't pick their brains. Now, Short of Peejay it seems as if most of these users have little to no experience in a race/track application. Although if I'm not mistaken Peejay is doing either Rally or Rallycross type events. The focus of my car will be mainly street use but I would like to attend maybe a couple track days per season (Minnesota Winters... Ew!) just to enjoy the car a bit more. I've yet to figure out a solid starting point for a setup. I'm currently at a stand still with my project for various reasons, the FC subframe swap being one one of the larger reasons. At this point it's either find a stock box and use FC spindles up front (tempting because i'd like to run some low offset wheels up front!) or Finish the subframe swap and make it work well. I don't have ANY seat time... I'll be picking up a 350z or FRS for that. If I can't find either of those I do have an FC sitting at home... Which would be a better starting point for my RX7 goals anyway
My current plan
-FC Subframe swap. I've already welded tabs to the subframe. I cut windows in the frame rail an inch to the rear of the factory mounting stud, installed crush tubes.
-Ground Control or T3 FB Camber Plates... I want to avoid notching the body for FC camber plates if I can!
-Matching Front and Rear Struts - Koni or Bilstein inserts in stock FC strut housings, AE86/Camaro/Mustang Based Rear struts? I need help here.
-175lb front springs, 150lb rear springs?
-Panhard conversion or KC Raceware Three Link Conversion? I do not have class rules to follow.
Worst case scenario, I'll be in contact with Stance Suspension or BC Racing and have a custom set of coilovers made... These will probably run $1400. If I could beat that, great! I've got the car sitting on GSL-SE rear springs and KYB GR-2 rear shocks. Plenty good to finish the build with!
There's lots of useful information beyond your shores too. Check out this mega thread on the FC subframe swap: http://www.ausrotary.com/viewtopic.php?f=4&t=148631
my converted subframe is explained here: http://www.ausrotary.com/viewtopic.php?p=2814653#p2814653
mine is done differently to most explanations on this forum. I have custom box sections and extensions welded on to allow the subframe to attach on to the factory chassis points (for engineer approval under local road laws here). This also restores factory angles and axle position.
i use 4 stud hubs from the US FC non turbo models with different bigger diameter and hat height rotors and custom mounts to accept FD calipers. This choice of rotors helps restore factory front track.
I've done mine essentially the same way you have. I had Dream In Rotary laser some 1/8 mild steel brackets out for me, but I question the strength of the method I used and will likely do it the same way you have just in double shear. However I still havent figured out the dampers situation, and actually getting the suspension geometry to work. So far in my research, the best advice I've seen is redrill the front LCA Pickup points and tune the chassis from the rear roll center. Obviously I can't tune rear roll center with the factory watts so that'll have to be addressed later on when I actually have the skillset to do so. I've picked up a couple of books I've been reading so I'm starting to get a better understanding of how geometry works.
I'll start poking around to see if I can figure out the FD brake setup... I'd really like to run some 15 inch low offset (somewhere in the +0~10 range) period correct wheels on this build. What is the smallest wheel that fits with the FD brakes?
I'm using custom ACBron Motorsport Ultimate coilovers. They use shock valving (with 40 levels of dampening adjustment), springs and camberplates suitable for a 1st gen but with an FC base mount.
smallest wheels with FD brakes are 16" (depending on brand)
Ps to allow a 15" wheel i really think you need to look at something like a Wilwood Dynalite billet caliper. These are lighter amd slimline allowimg you to stuff much bigger discs than what Mazda calipers allow.
-Ground Control or T3 FB Camber Plates... I want to avoid notching the body for FC camber plates if I can!
Why? it's like less than a quarter of an inch. You can't even see the notch when you do up the nuts. Here's a shot of my FB with FC BC Racing Gold coilovers:
-Matching Front and Rear Struts - Koni or Bilstein inserts in stock FC strut housings,
Don't do this. I wasted so much time trying to get this to work and you run out of travel extremely fast. This is a pic of a FC subframe with FC/FB struts welded together at maximum compression:
Granted, that's an 81 car and the GSL-SE struts are a fraction shorter but it's never going to give you much room to move. Just get coilovers.
You will have roll center issues due to the height of your watts linkage in the rear unless you change your setup. I can't help you there, I went IRS, but others can chime in with live rear axle suggestions I'm sure.
FWIW, when I made my new rearend, I lowered the Watts link pivot 40mm so that it would work better with the FC frontend.
Between making the pivot 40mm lower and the much larger Ford 9" pumpkin, I had to make the bellcrank 70mm taller.
No room for a Panhard unless I got rid of the fuel tank and the Racing Beat muffler. Not having sa fuel cell and having a quiet exhaust wins out over proper suspension geometry.
The main problem with the FC subframe in the FB chassis is the FC had low roll centers and the FB had high ones. This is a lot of why FBs tend to feel more "skittish" but also need less spring rate, especially in the rear since the roll couple gets shorter, not longer, with decreased ride height. Putting an FC subframe in an FB makes the roll axis really skewed and handling gets odd.
I'll start poking around to see if I can figure out the FD brake setup... I'd really like to run some 15 inch low offset (somewhere in the +0~10 range) period correct wheels on this build. What is the smallest wheel that fits with the FD brakes?
FC disks are 276mm, you can run 15s on those. FD calipers are a direct bolt-on to FC hubs, although you will have to change the hard brake lines that attach to the caliper. There's very little difference between FC and FD 4-pot calipers, they use the same brake pad and mount in the same way. I'm using the FC 276mm front disks with FD calipers and it works fine.
Why? it's like less than a quarter of an inch. You can't even see the notch when you do up the nuts. Here's a shot of my FB with FC BC Racing Gold coilovers: Don't do this. I wasted so much time trying to get this to work and you run out of travel extremely fast. This is a pic of a FC subframe with FC/FB struts welded together at maximum compression You will have roll center issues due to the height of your watts linkage in the rear unless you change your setup. I can't help you there, I went IRS, but others can chime in with live rear axle suggestions I'm sure.
Honestly, its more of me not wanting to do irreparable (for a lack of better words) damage to the vehicle. Which product line of BC did you go with? I'd probably go with the entry level BC BR or Stance Suspension if this is the easiest route to go with. My only reason for wanting to choose Bilsteins or Koni over coilover was my rather uneducated self feeling as if the valving would probably be better. Rear suspension I am still unsure of, right now the car just needs to roll so I can get brake/fuel lines plumbed and choose an engine setup for it. Leaning towards stock four link for now with the stock watts. I'll have to do some reading and see if I feel comfortable building my own panhard or watts. The KC raceware three link setup looks quite interesting. IRS is completely out of my comfort zone and would add another layer of unnecessary complexity to an already drawn out (two years!) project. I'd really like to drive my car again!
A rather well known race car is running a toyota rear diff, custom watts, and as I mentioned redrilled pickup points for the front control arms. They're tuning the roll center off the rear watts... clearly it's working for them. Is this a viable option? They've shared photos with me but I'm not sure they'd appreciate me publicizing the photos even though it was quite a while back. As I had mentioned before I'll be picking up a modern chassis to learn with for this year, as I have not a single second of track time to my name.
FC disks are 276mm, you can run 15s on those. FD calipers are a direct bolt-on to FC hubs, although you will have to change the hard brake lines that attach to the caliper. There's very little difference between FC and FD 4-pot calipers, they use the same brake pad and mount in the same way. I'm using the FC 276mm front disks with FD calipers and it works fine.
FD disks are 295mm and you need 16" rims minimum.
Turbo 2 Front brakes it is! I'll have to see if I can build a custom offset version of the wheel I'd like when push comes to shove, but until then It'll be rocking GSLSE wheels rear and my five lug FC GTU wheels up front. I've got spare four lug front hubs as well so that'll be an easy swap once I can get a machine shop to do the hard work.
FC calipers may foul on some aftermarket 15" wheels. In fact they even foul on my particular style of 17" wheels when using FC size discs.
I went for FD calipers because (a) they are more compact externally provide better wheel clearance; (b) FC calipers are getting really hard to find, at least in Australia they are. FD brake hardware (eg springs, clips and pad plates) are also more readily available.
FD calipers with FC diameter discs wouls be a good combo for smaller wheel sizes. Although I'd probably still go for Wilwoods for a 15" wheel, particularly when you look at the USD price for brand new wilwood calipers. Way better value than used Mazda calipers that WILL need to be rebuilt.
Here are some shots of my FC subframe install, pretty straight forward install, check out the 2nd Gen Mazda RX-7 coffee table book, it has 3 pages of how they used the FB as test mules for the FC subframe front and rear, great pictures and source material.
Had a friend convert his as well after seeing my install.
Honestly, its more of me not wanting to do irreparable (for a lack of better words) damage to the vehicle.
If you ever go back, it's the work of 10 minutes to fill the notches in with a welder and grind them flat again. It's really a very minor thing. Much easier than swapping hats over.
Which product line of BC did you go with?
Gold, it was really the only thing readily available where I live. But whatever you choose, you need that pillowball mount at the top, it makes a huge difference with wheel clearance. Using the factory strut mock-up that ultimately failed, I could barely get +45 offset rims on the front, they were practically touching the shock tube. With the coilovers they cleared with about 10mm to spare.
an already drawn out (two years!) project. I'd really like to drive my car again!
14 years and counting. But I get to drive it this year
A rather well known race car is running a toyota rear diff, custom watts, and as I mentioned redrilled pickup points for the front control arms. They're tuning the roll center off the rear watts... clearly it's working for them. Is this a viable option?
Sure. If they've identified the problem and are tuning it out, you need to learn from them. I used a sledgehammer option in the IRS to fix the roll axis problems but if you can tune that out with a modified watts and some repositioned LCAs then by all means go for it.
Personally I'd get that FC subframe in and get the thing driving. You might find the issues aren't as serious as you imagine, or you just don't care so much. After a couple thousand miles you'll be in a much better headspace to determine what you want to tune out and what you're happy to live with. At the very least any changes you make will be much more obvious.
If you ever go back, it's the work of 10 minutes to fill the notches in with a welder and grind them flat again. It's really a very minor thing. Much easier than swapping hats over.
Gold, it was really the only thing readily available where I live. But whatever you choose, you need that pillowball mount at the top, it makes a huge difference with wheel clearance. Using the factory strut mock-up that ultimately failed, I could barely get +45 offset rims on the front, they were practically touching the shock tube. With the coilovers they cleared with about 10mm to spare.
Sure. If they've identified the problem and are tuning it out, you need to learn from them. I used a sledgehammer option in the IRS to fix the roll axis problems but if you can tune that out with a modified watts and some repositioned LCAs then by all means go for it.
Personally I'd get that FC subframe in and get the thing driving. You might find the issues aren't as serious as you imagine, or you just don't care so much. After a couple thousand miles you'll be in a much better headspace to determine what you want to tune out and what you're happy to live with. At the very least any changes you make will be much more obvious.
I do agree to a certain extent getting the suspension in and driving it may be the best bet, however when the car looks like the photos below I can't help but to go for some sort of more "effective" attempt. I'd hate to keep asking questions rather than just getting out and working. However I'd also like to use this car as an exercise to learn and modernize. I've been actively looking for a more modern chassis to get my seat time issue resolved (350z seems to cater to my needs best). That was the original intent buying my FC but I'd starting to feel like the FC is a little too nice for the abuse I'd like to give it.
Originally Posted by Freeskier7791
With FC brakes I can run a 15" steel racing wheel, but need a 10mm spacer to clear the calipers pay attention to your roll center, that was a reason why I have kept my FB front subframe
That's the initial reason for the post. Roll centers, how to make the suspension work effectively OR finding an alternative way to achieve the big brakes and install Rack and Pinion steering. Currently reading some Fred Puhn and Carroll Smith books. What's your front wheel offset? I'd really like to put some 15x8 wheels on it that I see range from -15 to 10 offset. Just doesn't seem feasible to me without looking stupid or running wide over fenders, huge spacers out back.
Here's an Idea: Redrill the control arm pickup point (X) inches up on the FC subframe, FC spindle, Adjustable FB lower control arm with appropriate adjustable ball joint, and use the FB tension rods. Seems plausible but I haven't seen it done yet. Otherwise I've got to see if it's possible to weld an FC rack onto the FB subframe. I've heard of using S13 front suspension but this isn't well documented and who knows how it affects the geometries that I have a very minimal understanding of in the first place.
Whizbang (Alex) and I are on here all the time and can give you any further advice as to the subframe swap. Kinda bummed I wasn't even mentioned, yet I showed how to keep the factory FB steering wheel upper (indicator, electronics, cruise control, etc) with FC lower into a beautiful package.
My setup runs sleeves through the chassis tubes so you can get proper clamping force on the subframe without potential for damaging the "frame rails". It's a unibody car and they're relatively thin, so I added an 0.083" box tube around them throughout the length of the vehicle. Structure without stitch welding...
Your best bet with this is to run a 13BT to make the subframe worthwhile... Enjoy the nice new suspension (lower the rear roll center as previously mentioned), and have some power to back it up.
So many names to add, you've been a huge help with all the back and forth messages on Facebook messenger that's for sure!. Sorry about that one! All the Authors you've recommended to me have been a huge help as well. It's a shame life gets in the way of hobbies sometimes. This project could be much farther along than it is.
Honestly, I wish I could find a set of used FC front coilovers. The car is sitting on KYB GR-2s in the rear, GSLSE springs, I might just pickup the T3 "panhard conversion" purely because I cannot find some of my watts hardware... I'm just trying to save the budget for now to get it driving before I ball out on quality dampers and springs. I'll probably have to pick up a TIG welder to correct a couple mistakes I made while getting the subframe to fit too Indecisiveness is definitely a bad trait when it comes to getting this project done. I went with your method for mounting the front subframe. I cut windows in the frame rails and installed crush tubes/sleeves through the rails an inch rearward of factory. Welded the windows back up, however I left a small hole in the window to get a cavity wax wand inside. I regret the way I made my subframe mounts however- 1/8 steel plates lasered out, butt jointed to a piece of 1/4 plate at the bottom with no spacer. This will likely get redone before she's road worthy but for now it'll work.
For now, I'll probably get my S5 T2 block streetported when the time is right, run it NA for a while with the Kia 4.77 rear gears and a T2 trans.
As much as I dislike the T3 products, that panhard conversion would get you out of a lot of funk. I'd say do it, and lower the panhard pretty far down to match the new FC front end.
This subframe swap is getting quite popular. I am finishing up mine (hopefully this weekend). The car is a gsl-se crapcan endurance racer so without any consideration to practicality and street-ability it's not too bad a project.
This thread is about "Making it work" so in that vein I am most interested in anyone with real life racing experience, post swap.
Specifically: Lessons learned on the initial testing weekend. I understand roll center etc etc, but given that as a fact of the new geometry what did you notice on first testing? Did the car understeer? Did you need to change your front/back spring rate ratios? Did you NEED to put big sway bar up front? Was there excessive bump steer?
I have a custom panhard setup that runs parallel to the bottom of the diff so that should be helpful in evening out roll centers.
Specifically: Lessons learned on the initial testing weekend. I understand roll center etc etc, but given that as a fact of the new geometry what did you notice on first testing? Did the car understeer? Did you need to change your front/back spring rate ratios? Did you NEED to put big sway bar up front? Was there excessive bump steer?
I have a custom panhard setup that runs parallel to the bottom of the diff so that should be helpful in evening out roll centers.
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.
04-06-18, 01:29 AM
Indecisiveness is definitely a bad trait when it comes to getting this project done. I went with your method for mounting the front subframe. I cut windows in the frame rails and installed crush tubes/sleeves through the rails an inch rearward of factory. Welded the windows back up, however I left a small hole in the window to get a cavity wax wand inside. I regret the way I made my subframe mounts however- 1/8 steel plates lasered out, butt jointed to a piece of 1/4 plate at the bottom with no spacer. This will likely get redone before she's road worthy but for now it'll work.