Future Products: Boyesen's exhaust trapping valve

2-stroke power help
Efficiency is Key - Boyesen's trapping valve system is tied mechanically to the crankshaft to ensure perfect timing. The trapping valve opens and closes with every revolution.
Less unspent fuel - A 2-stroke's intake and exhaust ports open at the same time (1) so there's air/fuel loss through the exhaust port. Here (2) the valve seals the combustion chamber allowing the air/fuel mix longer to vaporize without the fuel/air mixture escaping the cylinder.
PROTO TESTING - Boyesen has put the exhaust trapping valve system on a Kawasaki KX 250 motocross engine for testing. You can see it inside the cylinder in the top photo.
Some folks have questioned if the future of 2-strokes is limited, due to emission concerns, but not Eyvind Boyesen. He sees a solution to inherent 2-stroke engine issues via an exhaust trapping valve.

Boyesen is an inventor and former top motocross racer who has always done his own wrenching and has a knack for coming up with new solutions to motorsport problems. Back in 1972 he started Boyesen Engineering in Pennsylvania and started creating products for the motocross world and now much of the snowmobile industry.

His firm makes reeds, dual reeds and now three-stage reeds to boost snowmobile engine performance. Then there's the Rage Cage and PowerWings that enhance intakes for most modern sleds. Boyesen now has a new prototype exhaust trapping valve. This valve is different from stock exhaust power valves in many ways. The trapping valve opens and closes with every engine revolution. In other words, the trapping valve closes the exhaust port so that NO fuel/air mixture escapes from the cylinder.

Valve comparison
Let's compare Ski-Doo's Rotax engine that's equipped with RAVE (Rotax Adjustable Variable Exhaust) valves. This is a simple system that works with spring pressure. With more engine rpm, the more engine pressure and the more the RAVE valve opens. When the engine pressure drops, the RAVE valve closes.

This is a great system for performance, it provides a small exhaust opening for low rpm and when it opens, it provides a large opening for the higher rpm. This power valve system makes the engine run smoothly on the bottom and top. But the problem with it, and with 2-stroke motors in general, is the intake ports and exhaust ports are opened at the same time. This means some fuel/air mixture escapes without being burned, which causes poor fuel economy and poor emissions.

Boyesen's new trapping valve is synchronized with the piston movement by mechanical means. By sealing the combustion chamber and allowing a longer time for the fuel to vaporize, one can eliminate poor volumetric efficiency or the loss of the fuel/air mixture in the 2-stroke engine. This elimination enhances the combustion process, which means more power and lower exhaust emissions.

More power
There's no doubt that all 4 OEMs are making better engines than ever before. Recent Big 4 fuel-injection systems are getting better performance and better fuel economy, a welcome, and mandated, situation.

Yet Boyesen claims its trapping valve system will work on any 2-stroke engine regardless of what fuel delivery is used. By using the trapping valve there is an opportunity to take the 2-stroke to another level. It's providing more power and torque, especially at the engine's low end.

When dyno tested, Boyesen says its engineers are finding 60% more torque on the bottom. They also found 20% more torque at 6,000 rpm and 20-24% more torque above 6,000 rpm. What this could mean is lower clutch engagement (maybe 1,500 rpm) and by engaging at lower rpm there will be less fuel used, creating further fuel savings.

In addition, using this new system there is no need for big pipes under the hood. Boyesen also claims there's less oil required when using the trapping valve, with less oil, there is a possibility of using a catalytic converter, which would make the 2-stroke exceed the EPA standards well into the future.

Here's a thought: how about a new E-fficient 600cc sled with a trapping valve, a small straight pipe leading into a catalytic converter and then into a muffler?


Boyesen is still testing this new system and hopes to bring it to the snowmobile market shortly. As soon as we get the word, AmSnow will let you know, so stay tuned!
More info: www.boyesen.com
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