<P> This system is still partially dependent on total loss lubrication (for the upper part of the piston), the other parts being sump lubricated with cleanliness and reliability benefits . The piston weight is only about 20% heavier than a loop - scavenged piston because skirt thicknesses can be less . Bernard Hooper Engineering Ltd . (BHE) is one of the more recent engine developers using this approach . </P> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2010) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2010) (Learn how and when to remove this template message) </Td> </Tr> <P> Many modern two - stroke engines employ a power valve system . The valves are normally in or around the exhaust ports . They work in one of two ways: either they alter the exhaust port by closing off the top part of the port, which alters port timing, such as Rotax R.A.V.E, Yamaha YPVS, Honda RC - Valve, Kawasaki K.I.P.S., Cagiva C.T.S. or Suzuki AETC systems, or by altering the volume of the exhaust, which changes the resonant frequency of the expansion chamber, such as the Suzuki SAEC and Honda V - TACS system . The result is an engine with better low - speed power without sacrificing high - speed power . However, as power valves are in the hot gas flow they need regular maintenance to perform well . </P>

The two cycle engine produces a power stroke on every