ProSolo Prep Work: Coil-Overs, Wilhelm Raceworks Suspension Parts | Project Toyota MR2

Update by J.G. Pasterjak to the Toyota MR2 Turbo project car
Feb 15, 2021

The plan for our 1991 Toyota MR2 Turbo all along was to have it ready for the traditional kickoff of the SCCA’s National Solo season, the Dixie National Tour, which usually happens in mid-March at South Georgia Motorsports Park. We’re running the car in the SCCA’s new Xtreme Street category.

But we were in for quite a surprise when the SCCA dropped a ProSolo 1—a single-course competition that incorporates ProSolo’s drag starts and relevant reaction times—right in our backyard at the Florida International Rally & Motorsport Park February 12-13.

This schedule addition seriously compressed our time schedule, but we felt like we could still pull off our plan to have at least a somewhat prepped—although probably not fully sorted—MR2 ready for our local ProSolo.

Thankfully we had some great suppliers ready to help. Alex Wilhelm of Wilhelm Raceworks is basically a one-man band, building bespoke MR2 suspension components in his Montana shop, but he was still willing to take the time to ship our kit piecemeal as he got parts from his suppliers to keep us working instead of waiting.

That great service allowed us to install our KW V3 coil-overs under the Wilhelm camber plates in advance of the arrival of Wilhelm’s roll center correction blocks and bumpsteer correction kit.

We were about to button everything up the weekend before the Pro, but when we got a notification that the last bits of our kit had shipped and would be here in time for installation—albeit maybe with a couple late nights—we decided to go for it.

We’ll detail the application and theory behind each piece in our entire suspension kit in future updates, but the laundry list looks like this: KW Variant 3 double adjustable coil-overs mount under Wilhelm Raceworks custom camber plates, which increase both static negative camber and front caster.

The KW V3 kit comes with 400 lbs./in. rear springs and 170 lbs./in. fronts, but we upgraded the fronts with a slightly more aggressive set of Eibach springs rated at 230 lbs./in. Wilhelm prefers an even more aggressive ratio of about .7:1 front to rear on spring rate. The Eibachs put us just under .6:1, but we figured it was a good place for our baseline, and springs are fairly easy to change on the KW struts.

Under the front and rear hub carriers sit Wilhelm’s roll center correcting spacers, which move the control arm down and provide more favorable geometry after lowering the car.

In the stock configuration, lowering the car puts the lower control arms at an angle that's higher at the knuckle than the connection point on the car, which lowers the front and rear roll centers to at or below ground level. This roll center creates a lot of leverage on the center of mass, actually increasing body roll after lowering the car. Spacing the control arms down puts them in a more favorable movement arc when subjected to roll and minimizes the effect of this roll center movement.

Lowering the car also changes the relationship of the tie rods to the knuckle, and can create situations where roll dramatically changes toe. Wilhelm’s bumpsteer correctors space their custom tie rods a proper distance from their connection points on the knuckles, minimizing toe changes at the front and rear of the car.

Installation was straightforward, with the only real trap being the bushings that must be pressed into the rear knuckles to connect the custom toe links. After deciding, “Sure, we can use a ball joint puller to do these on the car,” we removed the old shells without much fuss.

The new bushings, however, would not go in without serious mechanical assistance. So we removed the knuckles—really not that hard of a job, but you’ll have to remove the brake caliper and bracket, ball joint, rotor, ABS sensor (unhook it from inside the engine bay, as it's prone to breaking when removed from the knuckle) and nut off the end of the axle stub—and walked the assembly over to the hydraulic press.

We also tucked our bushings into a bag of frozen wings for a few hours to cool them down as much as possible. Even the press groaned a bit setting them in place, but they slid home smartly and fit brilliantly once seated.

With our complete suspension now assembled, we set the car on our Paco Motorsports hubstands atop our Intercomp scales for a quick and dirty corner-weighting.

Before we drive a car, we’re not looking for 0.0001% precision from a corner-weighting. Just close enough for us to get a feel for the balance and determine how we want to proceed after a few track or autocross laps.

Front camber was set to -3 degrees, rear camber was set to -2.4 degrees, front toe was zero, and we toed in the rear 1/8 inch total. When we completely replace a suspension like this, we like to have our first alignment done on a real rack at a real shop. We dropped off the car at The Alignment Shop in Ormond Beach, Florida, and got it back a few hours later set exactly to our desires.

So the next step is some driving, and our shakedown will be SCCA’s ProSolo kickoff at The FIRM. It’s certainly a site we know well, so we’re looking forward to seeing how our new hardware performs in action.

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