Editing Two-stroke engine (section)

====Piston-controlled inlet port====
[[Piston]] port is the simplest of the designs and the most common in small two-stroke engines. All functions are controlled solely by the piston covering and uncovering the ports as it moves up and down in the cylinder. In the 1970s, [[Yamaha Motor Company|Yamaha]] worked out some basic principles for this system. They found that, in general, widening an exhaust port increases the power by the same amount as raising the port, but the power band does not narrow as it does when the port is raised. However,  a mechanical limit exists to the width of a single exhaust port, at about 62% of the bore diameter for reasonable piston ring life. Beyond this, the piston rings bulge into the exhaust port and wear quickly. A maximum 70% of bore width is possible in racing engines, where rings are changed every few races. Intake duration is between 120 and 160°. Transfer port time is set at a minimum of 26°. The strong, low-pressure pulse of a racing two-stroke expansion chamber can drop the pressure to -7 psi when the piston is at bottom dead center, and the transfer ports nearly wide open. One of the reasons for high fuel consumption in two-strokes is that some of the incoming pressurized fuel-air mixture is forced across the top of the piston, where it has a cooling action, and straight out the exhaust pipe. An [[expansion chamber]] with a strong reverse pulse  stops this outgoing flow.<ref>{{cite book |first=Gordon |last=Jennings |title=Two-stroke Tuner's Handbook |chapter=Port timing |pages=75–90 |date=January 1973 |url=https://www.vintagesleds.com/library/manuals/misc/Two-stroke%20Tuner's%20Handbook.pdf |access-date=14 June 2024}}</ref>

A fundamental difference from typical four-stroke engines is that the two-stroke's [[crankcase]] is sealed and forms part of the induction process in gasoline and [[hot-bulb engine]]s. Diesel two-strokes often add a [[Roots blower]] or piston pump for [[Scavenging (engine)|scavenging]].