If you’re not too familiar with the Honda Z600, you’re in good company. The odd little front-wheel-drive hatchback was one of Honda’s first forays into the automotive market back in the early ’70s. Call it a toe in the water from a manufacturer who sold its very …
Taking Aim
Mike is a “play to win” kind of guy—a trait gained through his other hobby of long-distance running—so he examined the SCCA rulebook carefully for a class in which he could succeed. He hoped to recycle as much of his D Sports Racer as possible, which meant he’d be aiming at one of the Modified autocross classes. He also wanted to pick a class that had a low minimum weight; since he’s a lightweight guy, he felt that would give him an advantage.
“Originally I wanted to run in D Mod,” he explains. “Rules allowed up to a 2-liter engine but only 1400cc with a supercharger. A 1300cc Suzuki Hayabusa engine made 150 horsepower stock but could make big power with a turbo. I knew I could make more power than anyone else in the class because no one was using motorcycle engines.”
At the time, the D Mod minimum weight was 1000 pounds, perfect for the remains of Mike’s 940-pound D Sports racer. SCCA Solo rules also allowed the engine to be set back to the centerline of the wheelbase, and putting the weight of the engine and transmission in the center of the car would help achieve a low polar moment of inertia.
“While this would be very difficult to accomplish with a traditional automotive engine, the compact size and lighter weight of the motorcycle engine and transmission package lends itself to taking advantage of a true mid-engine location,” he explains. “So a second part of my plan was to build a mid-engine chassis that would locate the engine in what was once the passenger seat area.”
A Hayabusa engine and transmission—which weigh approximately 175 pounds together—would offset the weight of the driver and a fuel tank on the driver’s side of the car. The bike drivetrain’s lack of heft would also allow Mike to build an underweight car which he could then ballast up to the minimum for better chassis balance.
“In the end, the car with driver had a side-to-side weight difference in the chassis of only 7 pounds, and I had to add 140 pounds of steel floor pan ballast to hit the then-thousand-pound minimum weight requirement for the class,” he explains.
D Mod rules also allow a complete tube frame chassis as long as the original floor pan is retained. Mike built a wooden mock-up of the complete roll cage and chassis based on the outline of a Honda, and this served as a pattern for the chassis construction.
“My objective in the chassis layout was to keep all the weight centered and as low as possible with the goal of optimizing weight distribution and achieving a very low center of gravity,” he explains. “I incorporated the original D Sports 10-inch rims and brakes in the front, and fabricated a single combined rear brake rotor and chain sprocket, which was centered on a custom-made differential case in the rear.”
Mike is a big fan of Formula SAE competition and tried to adapt as many of its ideas as possible, such as the push-rod suspension layout and use of inexpensive motorcycle rear shocks as suspension units. He also took inspiration from Kurt Bilinski’s Kimini, a radical Honda-powered, Mini-bodied car featured in the November 2006 GRM.
“Kimini was an inspiration, as were the cars that are running in Formula SAE competition right now,” Mike says. “The front suspension was taken from my D Sports Racer, but the rear suspension is all new. Well, the shock placement and control arms are new. The axles and uprights are recycled from the sports racer.”
Based on some preliminarily calculations, Mike figured that he wouldn’t need Kimini’s expensive carbon body. A simple fiberglass body with small flares would work perfectly. As the plan came together, he needed a mold and a floor pan. “I bought a junk Z600 to take the body mold from,” he recalls. “It had dents and stuff, but we Bondoed them up to make it look nice as a mold. The first body was from fiberglass.”
Life Gives You Lemons
Halfway through the build, however, Mike’s plan for world domination—or at least a small part of it—was thwarted by a rule change. The D Mod minimum weights were the first to change, increasing twice during the build. Soon after, the class rules changed again, this time to prohibit motorcycle engines. The cornerstone element of Mike’s Z600 monster was no longer legal.
“The motorcycle engine was a critical part of my package that couldn’t be achieved any other way,” he says. “I was frustrated because the car had been built to the letter of the rules in D Mod, and now it was rendered obsolete by the rule change.”
Rather than totally scrap the almost completed car, Mike appealed to the SCCA. A subsequent rule change allowed the car to run in the B Mod class, the traditional home for open-cockpit sports racers and some formula cars. The car weights are lower and forced induction isn’t allowed, but wings are legal.
Converting the car to B Mod specs required some creative thinking, however. First to go was the stock floor pan and floor ballast. Second was the body shell. Mike was already committed to the Z600 shape, but he scrapped the fiberglass body for a lighter carbon fiber version to get the weight down. He also had to flare the fenders to completely cover the tires, a B Mod requirement.
After four years of part-time work, the completed car was just as Mike envisioned. The frame was light and strong, and the whole package was incredibly compact and efficient. This is a car designed for one thing only—autocross competition. Despite the class change, initial testing has proved that it does have the potential to be competitive.
“Even though rules changes killed most of our advantages, it is a good concept,” Mike reasons. “The engine has particular promise—it puts out 168 horsepower with a bigger-than-stock cam. On our first test run, Tom Berry, a national champion, set the second-fastest time of day.”
Unfortunately that first run killed the engine. The first iteration of the dry sump system didn’t have enough oil capacity, and the engine spun bearings. Mike soldiered on, rebuilding it and taking it for dyno tuning. And during that outing, the coupling on the transmission output shaft came apart.
Mike says the whole experience has been positive, although he did learn a lesson: “There is a risk in using the SCCA Solo rulebook as the basis for a significant race car investment, particularly if the car might take more than two years to construct. I do take some satisfaction in the fact that my car was ruled out of the D Mod class—that tells me that my design concept was definitely on the right track toward having a competitive advantage.”
And while Mike’s Honda might never win an SCCA national trophy—he finds solace in the fact that he can still run the car in the B Mod class—it already has fans thanks to its public debut at last fall’s Japanese Classic Car Show in Southern California.
As for the future, Mike does have one more trick up his sleeve. The Z600 has had such an astounding response from the public that he wants to build a street car based on the same concept. In the works is a N600-based hotrod with a front-mounted, rear-drive Hayabusa engine. If it’s anything like the Z600, the new car should be another show-stopper.
