Exhaust port timing control devices or power valves were introduced into a two-stroke engine in response to the customer's desire for more power. This was the most cost-effective way for manufacturers to increase power over the entire rpm range without significantly modifying their original engine designs, thus ensuring that the excellent power-to-weight ratio characteristics intrinsic to the two-stroke engine were maintained.
Varieties of different systems exist to control and operate these exhaust port modifiers. Some of the more sophisticated electronic systems incorporate auto-cleaning cycles at start-up, which help eliminate power valve sticking due to carbon build-up. The more economically designed systems, however, do not. As a result, the valves are more susceptible to deposits, which can reduce their functionality and significantly impact engine performance. Very heavy deposit formation can ultimately stick the valves and make them inoperable.
New power valve additive technology has been developed to inhibit deposit formation on these exhaust port modifiers and to ensure consistent engine performance over many hours of operation. This development work was facilitated by utilizing two in-house engine tests. The first test stand, containing a Yamaha
®
YZ125H1™ motocross racing engine, was used as a gross screening tool to rank a large variety of different additive chemistries with respect to their power valve cleanliness performance. The best performing candidates were then further evaluated in a second engine test stand, containing a Polaris
®
800 XC SP EDGE™ twin-cylinder snowmobile engine. This test procedure was specifically designed to serve as a finer discriminating tool for evaluating good performing lubricants and to further rank these oils based on their ability to minimize deposit formation. Various commercial lubricants were benchmarked using this engine test procedure, and the goal was to develop new additive technology that exceeded their current performance. Final proof of performance data was obtained by evaluating this new power valve additive technology in the field.
In summary, for variable exhaust port modifiers to operate well, carbon build-up and gumming must be inhibited. The new power valve additive technology developed is significant and important because it successfully minimizes deposit formation and ensures improved and consistent engine performance.
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