Project V8 RX-7: Part 15 – Major Suspension Overhaul

by Jeff Naeyaert

A couple of annoying sharp eyes on our last update a few weeks ago revealed that we had some KW suspension bits on our RX-7, so we've been forced to get off our lazy butts and write about them, some SuperPro bushings and a bunch of Improved Racing suspension goodies we put on as well in our attempt to make Project V8 RX-7 not only corner as well as it goes straight, but also remain tolerable and civil for daily driving. 

When we acquired our Project V8 RX-7 a dozen or so years ago, it came to us with a set of Koni Yellows, Eibach springs and a sad set of geriatric factory bushings.  While the car handled pretty well, we were getting a terrible rattle in the rear that made itself most present at higher speeds--clattering away in an annoying rythm as we cruised down the freeway.  Around 7 years ago we decided it was time for a suspension upgrade so we installed a set of Koni 28's with some stiff Hyperco springs from Tripoint Engineering, along with a full set of kidney-blasting solid delrin bushings to replace all the stock rubber bushings.   At the time, we thought since racecars had solid bushings, so must we, despite the many warnings of stupendous increased road noise and unforgiving ride.  Unphased by such warnings, Delrin went in to replace the stock rubber upper and lower control arm bushings, trailing arm bushings as well the rear differential mounts.  The only exceptions to our non-compliance policy were the factory pillowball bushings because they needed to articulate in more than one direction as the suspension traveled through its range of motion—Delrin is super solid and would bind at these points.  We replaced the factory pillowball bushings with genuine Mazda parts—6 of them at about $80 each. 

Fast forward to today and our suspension upgrades and butts are showing their age.  Those delrin bushings we installed required regular maintenance to keep them greased, translated ALL noise and harshness from the road's surface to our sensitive ears (odd, considering our hearing degrades over time) and lumbar, and probably bound in various places throughout the suspension’s travel under load due to a lack of compliance.  This, combined with an apparent lack of funding for new asphalt in SoCal, meant they had to go!  To add insult to injury, all of our "because racecar" mods did nothing to solve that annoying rattle in the rear.  Research suggested it was most likely bad rear toe links but we weren’t able to replicate the force or speed needed to emit a peep out of them in the shop.  The links look like they are probably old enough to vote, so they’re getting freshened up whether or not that’s the problem! 

Part I: Bet You Can't Guess Who We Got to Build Us Coilovers!

If you’re a regular reader of MotoIQ, you already know we are particularly fond of KW suspensions.  However, we were sad to learn they did not make any products for the FD RX-7 (or any RX-7 for that matter).   Rather than give up and go with something else though, we threw our weight around with the big wigs over there at KW and convinced them to throw some R&D resources at the idea!  A few weeks later KW's Dallas Brandt came down to our shop with a clipboard and a brand new set of V3’s to test fit on our FD!  

By now we probably don't have to show you what these look like anymore, but here you go anyway!  When the guys at KW agreed to help us out with a suspension they first had to acquire a 3rd gen RX-7, take the dampers off and measure everything before they could build this set--we aren't local to Sanger, CA where their R&D takes place, but thankfully someone else was and donated their car (or at least the dampers).  


With all-weather "Inox" non-rusting stainless steel bodies, OEM quality seals and the same valving as the top of the line Clubsports, the KW Variant 3 is perfect for the daily driver that sees occasional track use.  You don't get the top mounts and external reservoirs you get with the Clubsports, but unlike the Clubsports you do get a lifetime warranty.  Such is the case with all their "street" suspensions.


KW V3's compression and rebound damping are both independently adjustable.  This is the compression adjuster.  This newer design adjustment knob replaces the the older style that required a little pin tool to adjust.  And it's got numbers on it now so you don't have to go back to 0 and count clicks--handy when you're at the track trying to make quick adjustments underneath the car on the pavement!


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Tuesday, October 28, 2014 3:59 AM
Any extra noises from the Rod End Trailing Arm or Toe Links?
Tuesday, October 28, 2014 6:45 AM
An FD RX7 with LS swap is still one of my all time favorite car combinations that I have ever driven. This build is one turning out to be one of the best examples in the world. You have something special here Jeff. It has come a long way since I drove it :)

Jeff Naeyaert
Jeff Naeyaertlink
Tuesday, October 28, 2014 9:08 AM
Why thank you Billy, how sweet of you to say! :)

@Kaane, nope--nothing I can hear over the rest of the car at least! Time will tell with the rod ends but at least if they ever do go bad I can replace just those pieces with whatever grade of rod end I want.
Mike @FIGS Engineering
Mike @FIGS Engineeringlink
Tuesday, October 28, 2014 9:20 PM
I certainly appreciate the press out on that front LCA. Similar to what we have had to do on Lexus SC bushings.
Thursday, October 30, 2014 7:08 AM
Moving the shock mount inboard reduces its effectiveness, meaning you would have to get a harder shock to compensate
Thursday, October 30, 2014 9:16 AM
flip - I think you're referring to the lower control arm pivot they were talking about moving inboard for clearance. That is the pivot for the trailing arm, not the shock. The shock mounts to the upper control arm. Moving that pivot inboard might slightly reduce the leverage it has on the arm and allow for a bit more movement, but it looks pretty sturdy and probly doesn't allow for much movement anyway.
Thursday, October 30, 2014 10:47 AM
So, are we taking bets on which MotoIQ project is the fastest around the track? Between the power and the newfound suspension, I have a feeling the FDV8 might give everything a run for its money.

Also, does this mean KW is going to market FD parts now?
Thursday, October 30, 2014 11:05 AM
Burninator, you're right! My mistake.

Now that I realize that's a trailing arm mount, besides what Burninator pointed out, it looks like there isn't much room to move the mounting point inwards, the arm would contact the subframe (it appears to be channeled for the trailing arm)
Jeff Naeyaert
Jeff Naeyaertlink
Thursday, October 30, 2014 11:31 AM
There's enough room to move it in a little bit, in fact Battle Version makes an lower control arm/trailing link set that has a few different mounting points on the LCA. As it turns out though since we've gone with the widebody kit we've gained enough outboard clearance to run any tire we want without issue.

@Protodad I doubt KW plans to produce the kits in quantity but if one were interested I certainly wouldn't hesitate to contact them! As for being the fastest around the track I wouldn't take that bet if the Team America GT-R gets sorted out ;)
Thursday, October 30, 2014 7:32 PM
The stock cast LCA appears (from the picture) to likely be much stiffer than the fabricated arm, especially the section which is primarily in bending between the trailing arm mount and the rear upright/knuckle. Notice how the stock piece carries bending loads right around the trailing arm bushing bore by using stiffening webs, but the fabricated piece carries loads right into the sides of the tubing for the bushing bore. It looks like the bushing bore is really heavy wall (or is there a round plate welded to one side?), which is an easy way to reduce compliance of an otherwise open tube section (helps make a circle not turn into an oval), but a poor substitute for a better method to bypass the loads in the area of those outer two bushing bores. The gusset helps reinforce the weld joint and prevent cracking, but doesn't do much to help compliance because the bushing bore is still a flexible oval between the gussets and along the entire bushing axis. If you take the lid off of a peanut can, most of the can is still flexible even though the bottom end is closed and rigid...
Jeff Naeyaert
Jeff Naeyaertlink
Thursday, October 30, 2014 10:23 PM
You make a good point Fabrik8; I don't know enough about either the stock or SuperPro design considerations to offer anything other than conjecture but I will definitely share your thoughts with them as we test these. Appreciate the input!
Saturday, November 01, 2014 5:09 PM
Team America GTR isn't s true project car. If it was, you'd have to include the FXMD NSX ;)
Jeff Naeyaert
Jeff Naeyaertlink
Saturday, November 01, 2014 5:30 PM
hey, it's in the Projects drop down menu... the NSX isn't :(

the gt-r's build was followed pretty close while FXMD was only a feature. I blame you, Billy!
Saturday, November 01, 2014 7:11 PM
Not to dis TA but using the last update I think it's fair to say this project would handily beat it around the track. Maybe not in a few more weeks.

Also, there is another project Gtr. Course, I can't wait for that one to fall out of its warranty period...
Jeff Naeyaert
Jeff Naeyaertlink
Saturday, November 01, 2014 7:19 PM
Lol, too soon! The RX-7 is on jack stands awaiting more goodies so it's not beating anything at the moment.
Techno Duck
Techno Ducklink
Tuesday, November 04, 2014 5:07 PM
Ive had the KW V3 on my LS1 swapped 944 Turbo for a few years now and they have been great. One of the best dual purpose setups available i think. I replaced Koni Yellows with stock springs and the road manners improved greatly. What really surprises me is how well they do on the track for how good it rides on the street. Great writeup though and awesome build.. i wish my paint looked that good, its more of a road rashed tomato red color now after 26 years and many track miles.
Mysta Joe
Mysta Joelink
Thursday, November 13, 2014 12:01 PM
Hey Jeff, I know you said the KW might not produce the suspension for the FD. But what do you think about the Superpro rear lower control arms and the Improved racing trailing arms and rear toe links becoming available?
Mysta Joe
Mysta Joelink
Thursday, November 13, 2014 1:16 PM
Would it be possible for you to also tell us the spring rates that were used for this special V8 set up....
Jeff Naeyaert
Jeff Naeyaertlink
Saturday, November 15, 2014 11:35 AM
I can't even hazard a guess on that, Joe.. You might call Improved Racing though and see what the likelihood of them reviving that stuff is. I'm sure if there was enough demand for a batch they'd produce them.

Springs are 70N front/60N rear
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