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Shifter Kart Engines: Opportunities from Spec to Open Classes

About 10 years ago shifter kart racing burst onto the American karting scene promising a driving and racing experience more like an open wheel formula car than the traditional 100cc or Briggs-powered kart could provide.

By Len Emanuelson

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Like many forms of racing in this economy, shifter kart racing is in a state of change. With substantially more power, a six-speed sequential gearbox and 4-wheel brakes, they certainly delivered "bang for your buck" performance. Probably the biggest testament to the value of racing shifter karts is the career path of Scott Speed who went virtually from shifter kart champion to a ride in F1.

Initially the engine of choice in the U.S. was a 125cc motocross engine with Honda being the predominant brand. After a few years of “Moto” engines the dedicated Italian 125cc kart shifter motors migrated here from European Formula C shifter racing. They became known as ICC engines with brands like TM, Pavesi, Vortex, Maxter and many others. They were nearly race-ready out of the box and they thrived with broad, high rpm power curves. For the last few years these dedicated ICC kart motors have become the backbone of the Pro classes in shifter kart racing.

However, what started out as affordable, entry-level racing soon escalated to a point where fewer and fewer people could afford the top-notch equipment needed to be competitive. A national-level fully prepared ICC engine will cost a racer about $7,000, and if you plan on getting serious about your racing, you’re going to need a spare backup engine too.

A fully modified Moto engine costs about the same amount of money and produces equivalent power to an ICC, however they have much different torque curves. Open Moto engines have fallen out of favor with pro racers because the brutal low and mid-range torque of these engines negatively affect the handling of today’s “softer” shifter kart chassis that are developed mostly in Europe for ICC style engines.

Of that $7,000 engine cost approximately $5,000 is spent on the initial ICC engine purchase leaving about $2,000 for the engine builder. Let’s see…$2,000 to build a one-cylinder engine that you can hold in your hands – it sounds pretty attractive but read on before you sell your CK 10.

As shifter karts grew in popularity with Hollywood stars and NASCAR heros like Ricky Rudd going public about how great they are, many people with no karting or racing experience went out and purchased a shifter kart from a local shop, and took it out once only to realize how far over their heads they were. They immediately put their shifters up for sale and moved on to some form of entertainment a little mellower.

Kart shops now have a much better alternative for the newbies. They are called TAG (touch and go) karts and although they still have 125cc water cooled two-stroke engines, they are fitted with an electric starter and centrifugal clutch instead of a gearbox, and are much more friendly to drive although still extremely fast.

Many of these factors plus the downturn in the economy has spawned the Spec Honda classes that make up the bulk of shifter kart racing today. Spec Honda uses a CR125 Honda engine with few allowable modifications. Yet the racing is fierce, and you need a professionally prepared engine to be competitive. Spec Hondas are more cost effective for the racer for both the initial purchase and the race-to-race cost of maintenance. All successful Honda 125 kart engines begin life as engine kits from Honda.

For approximately $2600 you get a box full of individually packaged engine and transmission components that must be put together into a running assembly. There are basically two model years only that are used, the ’99 cylinder and head assembly and the ’01 cylinder and head assembly. Most of the other parts in the engine kit are interchangeable, but if you are planning on buying an old CR 125 motocross bike and using the engine, it had better be a ’99 or ’01 or you’re just spinning your wheels.

To take a closer look at today’s shifter kart engine technology we visited Darcy DeCoste’s engine shop that is dedicated to shifter kart engines and GP motorcycle two-strokes. Darcy’s shop is located in Santa Paula, California a little northwest of LA. From this location Darcy and his brother Vernon have turned out championship winning shifter kart motors of all kinds for years. Racers like Phil Carlson, Matt Jaskol, Jason Bowles, Brendon and Ryan Phinny and Conner DePhilippe are just a few riding DDR power to victory.

We first wanted to get a grip on all of the power numbers being thrown around the pits to see what engine builders should be shooting for. Darcy has a water brake chassis dyno that once belonged to Yamaha. He likes it because he can do steady state testing, and he can also run the kart through the gears and check the clutch. He claims that his water brake is 10-16% more conservative than most DynoJets, and the power numbers he shoots for with a fully prepped ICC or “open” moto engine is in the 43-44 hp range. Darcy said that both styles of engines make about the same peak power.