Porting and Polishing Two-Stroke Motorcycle Engines

Here's how shaving off miniscule ammounts of metal can drastically improve your speed.

two-stroke cylinder porting
Cutting metal for more speed and better resultsJulia LaPalme

In the early 1970s, motorcycle tuners were chasing a magic formula to improve the power and efficiency of two-strokes—simple, lightweight engines found in many on- and off-road bikes from that era. Ted Boyko began porting cylinders 45 years ago, when the two-stroke craze was at its peak, and he’s still at it today.

“It was all the guys with Yamaha RD350s and 400s,” recalls Boyko, leaning against a wooden workbench in his well-lit shop, Boyko Racing, in Costa Mesa, California. “That’s when it first went off the hook. Then, you had the RZ350s in the ’80s, which were liquid-cooled and even crazier.”

Boyko is considered an expert at modifying intake, transfer, and exhaust ports—the angle, shape, and size of which can yield dramatic changes in engine character and performance. From the factories, the former racer says, those critical passageways are sometimes partially blocked by casting slag left behind by the hastiness of production-line machining processes.

Boyko outlines the basics of what many consider a dying art. “You want to push fuel to the spark plug quicker without exhaust gases escaping excessively,” he says. “I polish the exhaust port and the head so that carbon doesn’t adhere to them, but if it does, it’s easier to clean off. On the intake side, a rough surface will help atomize fuel and keep it moving. The texture will keep the fuel loose—turbulent.”

Every miniscule bit of metal that Boyko removes with his handheld carbide-tipped rotary grinding tool is ultimately intended to improve the function and efficiency of the engine and its components.

Pointing to a freshly modified Honda CR500R cylinder, Boyko says, “One wrong cut, one slip, and I have to eat the cost of this whole thing. It’s definitely a challenge, but it’s important to cater the engine to the person in control of the throttle. Adjusting these engines for each individual’s style can make or break his or her chances for a podium finish. For me, personally, it’s all about saving privateers from having to fork out so much money.”