“The two-stroke is saved!” That was what we said in the July 1996 issue of Dirt Bike. At the time, we were sweating out new smog regulations from the California Air Resources Board that would outlaw two-strokes on public land. If California fell, we said, the rest of the country wouldn’t be far behind. Honda’s answer to the crisis was the EXP-2. This was a two-stroke dirt bike that used “Activated Radical Combustion” to more effectively burn gases in the combustion chamber.
The key to the design was an enormous power valve operated by a CPU. This power valve would, at times, close off 90 percent of the exhaust port. This would increase cylinder pressure at the precise moment needed to cause combustion, sort of like a diesel. A spark plug wasn’t actually necessary once the engine was up to the right temperature.
Honda dumped huge resources into the project and actually raced the EXP-2 in Baja and in the Paris Dakar Rally. Dirt Bike’s staff got to ride the bike and was impressed with the performance. We came away from the test saying, “If this is what two-strokes will become, there’s something to look forward to.”
So what happened to the project? Two things. The first was a further tightening in emission regulations that made even the EXP-2 look dirty. A bigger factor was the 1998 Yamaha YZ400F. That bike demonstrated to Honda officials that the public would accept four-stroke dirt bikes. The EXP-2 program was abandoned just as the four-stroke age dawned. The only lasting legacy was the infrastructure that it left behind. Honda’s small off-road racing department used the parts, gas cans and tools that were purchased for the EXP-2 racing ventures for years in its Baja program. o
For more two-stroke hardware check out our Behind The Build feature of Honda CR250R project bike. Click the image below for more!