Two Strokes of Genius

By Scott Lear
Jan 3, 2017 | two stroke | Posted in Features | From the Oct. 2016 issue | Never miss an article

History casts a special light on those who innovate and create strange forks in the road along the way. Frequently these ideas become dead ends– some because they didn’t work, and some because they worked so well that they became illegal–but occasionally an unconventional approach grants a competitive advantage too awesome to ignore. At the club level, there are many potential reasons to innovate. Some are budget driven, others are inspired by a sense of competition, fun or the desire to simply be different. The Miller family has been racing at the top tier of SCCA club competition for decades, and while father Jeff and son Jason have tallied many victories over the years, they’re not doing things quite the same way as their fellow racers. Instead, their decades of success have been powered by an engine that’s truly unique in the world of modern auto racing: a Kohler-derived, two-stroke flat-six.

Don't They Make Faucets?


Wisconsin-based Kohler is best known for its plumbing fixtures, from faucets and water fountains to toilets and showerheads. Kohler also has an engine division, however, and it produces Kohler-branded two- and four-stroke gasoline and diesel engines in a wide variety of sizes, from really tiny to pretty darn big. Generators, small recreational vehicles (like ATVs and snowmobiles) and lawn tools are just some of the places you may find a Kohler engine. Jeff Miller, who started racing SCCA B Production Corvettes in 1968, joined the Kohler company in 1970 and decided to bring his work home with him. “We saw D Sports Racers that were running around in the SCCA,” he recalls. “We decided we’d build one of those with one of Kohler’s snowmobile engines.” Jeff campaigned a Kohler-powered Lola in C Sports Racer and D Sports Racer as well as the under -2-liter Can-Am class, and he secured SCCA national championships in 1976, ’77, ’78, ’81, ’83 and ’96. “It was originally a three-cylinder Kohler snowmobile engine, 660cc in an 850cc class,” Jeff explains. “It was somewhat successful in a very small car we called the Mighty Mite.” The Mighty Mite used go-kart wheels all around, and Jeff reports that it was very fast. “We transitioned out of that into a normal-sized car, and we upgraded the Kohler to a four-cylinder, flat-opposed engine,” he continues. “That engine was being designed for a military drone application. I was a corporate pilot for Kohler, and I used to travel up to the Canadian two-cycle plant and snoop around. I saw this [flat-four] engine on the chief engineer’s desk and said, ‘This will make a fabulous DSR engine!’” Jeff and his crew at Wynnfurst Racing started developing the four-pot two-stroker for competition in 1975, when he reckons they finished about half the races while working out the kinks. Around this same time, the Miller family was developing another component for their race team: Jeff’s son, Jason, now 41. Jason has many early memories from being a toddler at the track in the 1970s while his dad began his impressive run of SCCA championships. “Who at that time wouldn’t want a father that few airplanes and drove race cars?” reminisces Jason, now himself a Kohler employee and SCCA racer. “That was exciting to a 6-year-old kid. I went with my father to a lot of the races; a lot of my responsibilities were things like professional wheel polisher. I spent countless hours cleaning wheels and doing whatever I could to help my father go faster.” When Jason reached the age of 11, he was racing karts and continuing to learn the mechanical side of things from his father and the other crewmembers. The SCCA didn’t allow competitors under the age of 18, but once he was old enough he began running in the D Sports Racing class. “I remember vividly that I wanted to race so badly in the June Sprints,” Jason says about his first eligible year of competition. “My dad said, ‘There’s the engine, there’s the car, figure it out.’” His dad motioned toward a spare engine block and an incomplete chassis. Jason got the car running in time, though he’s pretty sure it didn’t make it all the way through that first race. “Getting the best equipment was not really an option at the time, but getting a car with four wheels and an engine was the opportunity,” he notes.

Refining the Recipe


In 2006, once Jason had demonstrated his racing chops and won his share of events, he and his father decided to try merging a Kohler two-stroke with a more contemporary chassis. Starting with a West/Stohr D Sports Racer chassis, they made the necessary modifications for a four-cylinder Kohler engine. “We found out quickly that it was not going to be competitive as a result of the rules and the weights at the time,” Jason explains, “so for 2007 we converted it into a C Sports Racer with a six-cylinder.” In the many years that Wynnfurst has spent developing and refining the basic Kohler engine design, much of their focus has been on longevity. Racing what is essentially a one-of-a-kind design means there’s plenty of work to be done, and every race is partly a test session. “We kept refining the pieces over the years,” Jeff says, “better pistons, better valves, better materials throughout.” Certain upgrades have come with material advances, such as the carbon-fiber Moto Tassinari reed valves that let air into the crankcase. The compact powerplant displaces less than 1.5 liters, but as Jeff notes, “It’s about 280 horsepower, 160 ft.-lbs. at 10,000 rpm.” Instead of relying on the original casting, Wynnfurst now machines their own engine blocks from a single billet of 6061 T6 aluminum. “The block is something that never fails,” states Jeff. “We might have a piston seizure or a cylinder failure, but those are all individual components, like a Porsche or an aircraft engine. The crankshaft is a built-up part: You can press it all apart and put new rods and bearings on it and go again.” The team dabbled with fuel injection a number of years back, but the system was so costly that it exceeded the value of the engine itself. They’ve stuck with downdraft Lectron carburetors, a cost-effective solution that lets them tune for top-, mid- or low-end power, depending on the track. Considering the low torque output from the engine, they opt not to run as much downforce, playing up the high-speed strengths of the rev-happy two-stroke. We built [the chassis] specifically to take advantage of the engine,” says Jason. “At tracks like Daytona and Road America, the engine-and-car combo is very good. I often get, ‘Wow, you’re going so fast on the straights,’ but you give up a lot of stability and corner speed as a result of the smaller tires and less frontal area.” Jason explains that the two-stroke powerplant has some quirks of its own and requires precision above all else. “The big difference with a lot of the cars I run against is the torque,” he notes, citing the relatively low amount of twist from the small, high-revving two-stroke. “It’s all about momentum. You need to be very accurate in terms of your shift points. If you’re in the wrong gear, the car will nearly stop.” At the 2015 SCCA Runoffs at Daytona, Jason’s car qualified third, although his maximum speed on the straights was the highest in the Prototype 1 group, and second only to the considerably more powerful GT1 cars for outright velocity. Unfortunately, an aftermarket component’s failure led to an early retirement from the championship race. “Daytona was an exciting experience,” Jason recalls. “Obviously we didn’t win, but we had a lot of fun and we learned a lot. My team did a fantastic job of really executing problems when they occurred and working through it.”

Eyes on the Prize

Rupert Berrington Photo

Rupert Berrington Photo

The Millers are already looking ahead to this year’s Runoffs at Mid-Ohio, a favorite and familiar track for Jason. “It’s a driver’s track; you can make up a lot of ground just in terms of skill,” he notes. The team is going back to paddle shifters for the sequential gearbox this time, which should help Jason keep the Wynnfurst Kohler P1 in the meaty part of its powerband. They’ll also run more wing than they did at Daytona to help mash the sticky Hoosiers into the asphalt. “Hoosier Tire has just been unbelievable for us. Those guys and the development of our car–I can’t say enough about them,” Jeff beams. “Enginewise, we’ve improved some things that we didn’t realize were a problem until the long, fast track at Daytona brought out a few nagging issues,” he continues. “We feel like we have a much better unit this year.” Jason is hoping he’ll be able to add to his father’s legacy by putting another Runoffs trophy in the family cabinet. “My dad was very successful at the time. Either he would win–and it was often domination–or he’d break. There was no in between,” he explains. In the years the Millers have been racing for a championship, they’ve come close. It’s hard to bet against them, assuming they can get a reliable, strong run out of their unconventional racing package. As Jason emphasizes, “There’s only one in the world, and we’re the ones who have it.” Jeff, meanwhile, has many roles on the team, but it’s impossible to understate the support and belief he holds in his son on track. “I think,” Jeff says with the certainty of a proud father, “you’re going to see Jason come out on top.” “It’s all about momentum. You need to be very accurate in terms of your shift points. If you’re in the wrong gear, the car will nearly stop.”

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View comments on the GRM forums
kb58 Dork
1/3/17 4:46 p.m.

I don't recognize Scott's name as a GRM writer, but given that normal folks don't start with "History casts a...", I bet he is.

[Edit] I spoke too soon. The article above refers to a "fat-opposed engine" and a "fat six". Scott, you're okay, you're one of us!

JG Pasterjak
JG Pasterjak Production/Art Director
1/3/17 5:32 p.m.
kb58 wrote: I don't recognize Scott's name as a GRM writer, but given that normal folks don't start with "History casts a...", I bet he is. [Edit] I spoke too soon. The article above refers to a "fat-opposed engine" and a "fat six". Scott, you're okay, you're one of us!

Scott was in-house office staff for a decade until an adorable daughter stole him away a few years ago. He still supplies words from time to time, though. Love seeing his name in the book.

kb58 Dork
1/3/17 7:15 p.m.

Ah kids, stealing us away from fun cars when they're born, then terrifying us with them when they are teens.

Kreb GRM+ Memberand UltraDork
1/4/17 9:12 a.m.

I have to say that this inspires yet another hair-brained scheme to add to my list: Find a motor that I like that has a separate block and cylinders and redo it as a two-stroke. It'd be loud, obnoxious, and probably take five years out of my life to pull off, but what the hell!

MadScientistMatt PowerDork
1/4/17 9:16 a.m.

I hadn't realized that it was the same company behind Kohler engines and Kohler faucets.

stuart in mn
stuart in mn UltimaDork
1/4/17 12:43 p.m.

Love those exhaust pipes sticking out the back.

HappyAndy PowerDork
1/4/17 1:18 p.m.

I'd love more information about that engine! Please

kb58 Dork
1/4/17 2:12 p.m.

I was at a hill-climb event and someone had a 2-stroke formula car type thing with four pipes sticking straight up. Hearing that thing revving up under the freeway underpass that was the starting line (really!) was pretty incredible.

Jerry From LA
Jerry From LA SuperDork
1/4/17 2:37 p.m.
HappyAndy wrote: I'd love more information about that engine! Please

I can't remember which issue it was but GRM went into more detail in the print version.

racer_tom New Reader
1/4/17 7:36 p.m.

"From the Oct. 2016 issue"

chuckles HalfDork
1/4/17 7:39 p.m.

Got to make some serious noise.

Tom1200 HalfDork
1/5/17 12:30 a.m.

I love the smell of bean oil in the morning; as someone with a two stroke powered single seater (Formula 500) and former motorcycle racer I absolutely love two strokes. They are lighter, more powerful and do not grenade in spectacular fashion like 4 strokes. Now this car is a special case but two strokes also tend to be cheaper to maintain as well.

An example is the F500; 100 horsepower from a 500 twin in stock trim. Light mods like twin pipes and some other small mods would bump it up another 20hp. I was bummed when the Japanese manufacturers bailed in two strokes for most of their products. Race bikes where at the 400hp per liter level (factory bikes).

The old CSR DSR now P1 P2 class cars offer phenomenal performance; with our old DSR we set local track lap record that was within a couple of seconds of Mike Lewis' ex Roush Trans Am car. I've drove an early Stohr chassis a number of years ago and that was a huge leap in downforce compared to our home built car. With a 200 plus horsepower two stroke I imagine the chassis would be an absolute weapon.

4/27/17 1:56 a.m.

Man I love this thing! Since being "on the pipe" is so critical, what about a dual-clutch 8 speed transmission instead? Makes me miss my '72 Kawi 750 Triple...

759NRNG Reader
4/27/17 8:17 a.m.
maj75 Reader
4/27/17 8:20 a.m.
ucantcme wrote: Man I love this thing! Since being "on the pipe" is so critical, what about a dual-clutch 8 speed transmission instead? Makes me miss my '72 Kawi 750 Triple...

I had a '74, Candy Purple. Loved that bike! Given the prices for these bikes now, I wish I still had it. I still shop for one, but I can't really justify spending that much on a decoration, because I'd never ride it around here.

759NRNG Reader
4/27/17 8:23 a.m.
759NRNG Reader
4/27/17 8:27 a.m.

My very first street bike was/is a Yamaha RD400C with custom it

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