Project V8 RX-7: Part 15 – Major Suspension Overhaul with KW Suspension, SuperPro and Improved Racing Components

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!