crazy, mental good

Ever since AMG's Hammer pounded its way into the automotive scene, the name Hartmut Feyhl has been associated with smooth, powerful engines capable of transforming an everyday driving experience into something truly unique, without compromising comfort or reliability. Feyhl cemented his reputation as one of the world's great engine-builders in 1989, when he left AMG to form RENNtech. Regarded as America's foremost authority on Mercedes-Benz and one of the premier aftermarket tuning firms in the world ... it was a passion from Feyhl's childhood that led to his latest innovative foray into motorsports: karting.

"When I was young in Germany, we used to race every weekend. I would work on the kart myself, then. Really it is how everything else got started," explains Feyhl. "Now I am a little bit older, and I don't want to play around with these little 2 strokes that have to be rebuilt all the time. I still love karting, but I want to just go to the track and have a good time with a very fast kart - so when I saw Paul's engine, I knew that this was something I wanted to be a part of."

That "Paul" is Paul Woelfle, a genuine legend in kart racing who's engineering skills have helped launch the careers of drivers like Nick Heidfeld, Heinz-Harald Frentzen, and Ellen Lohr. "Paul's engine" is the Aixro XR50 rotary kart racing engine, currently being imported and developed for stateside applications by RENNtech's sister company, RENNtech Karting.

"It's really an incredible design. I can't get enough of it." explains Feyhl - who, after years of getting extreme horsepower from his own engines, isn't known for getting unusually excited about such things. This engine, however, seems to be the kind of thing everyone is getting excited about. Alan Dove (Karting 1's admittedly skeptical tester) wrote that the Aixro was "a life-changing experience ... simply the best kart engine I have ever driven. It is crazy, mental good."

There are several key aspects to the design that create the Aixro's "crazy, mental good" package. Chief among these is the engine's Wankel-derived rotary design (similar to that used in the Mazda 787B racecars). Rotary engine designs produce huge power and torque from a relatively small displacement and an exceptionally small package. In more practical terms, the Aixro engine is smaller and lighter than conventional kart engines, yet produces more power. "Almost 50 horsepower, actually," explains Feyhl, who dyno-tests each engine prior to delivering it to his customers. "Also," he adds, "the motor is almost totally free of vibration, so the chassis doesn't shake itself loose. If you are used to the normal kind of buzzy go kart engines, the smoothness of the rotary becomes a very unique experience."

As significant as the Aixro's smoothness and power is, however, it may be the low maintenance requirements of a rotary that set this motor apart.

A rotary design uses significantly fewer moving parts compared to a conventional 2 or 4 cycle motor. Feyhl tells us that "if you maintain the engine correctly, and observe the rpm and temperature ceilings, you should easily get 100 - 150 hours before you need to do any kind of real service." That kind of engine life is unheard of in most karting circles, and helps to create the kind of "turnkey karting" experience many hobbyist drivers are looking for. "It's exactly what I want from my go kart. If I wake up on Saturday and want to go to the track, I know that I won't spend half the day working on the engine. With the Aixro, I can spend my weekend driving, instead of wrenching, and still have the fastest kart on the track!"

RENNtech Karting recently began offering the Aixro with an integrated starter package, delivering a real "Touch And Go" driving experience that is comfortable, reliable, and FAST! The motor itself can be fit to almost any shifter chassis, and has seen service in chassis from Sodi, Birel, Tony Kart, and more. But even with almost 50 hp, some people want more. Feyhl is ready to oblige these customers! "We quote 48 hp now, but we're constantly developing the package. With some of the tuning options we're currently developing, that number could easily top 55 or possibly 60 ... but 48 is probably enough for most people."

With the rest of the pack about 20 hp down on the Aixro, that's prbably the most believable thing about this unbelievable engine package!