It is critical that the burnt gasses are scavenged from the combustion chamber, in order to make room for as much unburned gasses as possible. The gasses travel up the backside of the cylinder and loops around in the cylinder head to scavenge out the burnt mixture gasses from the previous power stroke. Meaning that the unburned mixture gasses are flowing out of the transfers and merging together to form a loop. The pressure in the cylinder must blow-down to below the pressure in the crankcase in order for the unburned mixture gasses to flow out the transfer ports during the scavenging phase.Ģ) Now the transfer ports are uncovered at about 120 degrees after TDC. The blow-down phase has started and will end when the transfer ports open. A pressure wave of hot expanding gasses flows down the exhaust pipe. At about 90 degrees after TDC the exhaust port opens ending the power stroke. This pressurizes the crankcase causing the reed valve to close. These four drawings give an explanation of how a two-stroke engine works.ġ) Starting with the piston at top dead centre (TDC 0 degrees) ignition has occurred and the gasses in the combustion chamber are expanding and pushing down the piston. That is how a two-stroke engine completes a power cycle in only 360 degrees of crankshaft rotation compared to a four-stroke engine which requires 720 degrees of crankshaft rotation to complete one power cycle.
There are different phases taking place in the crankcase and in the cylinder bore at the same time. Use the guide at the end of the chapter to map out your strategy for changing engine components to create the perfect power band.Īlthough a two-stroke engine has less moving parts than a four-stroke engine, a two-stroke is a complex engine because it relies on gas dynamics. Use this as a guide to inform yourself on how changes in engine components can alter the power band of bike's engine. The most common mistake is to choose the wrong combination of engine components, making the engine run worse than stock. A myriad of different aftermarket accessories is available for you to custom tune your bike to better suit your needs. Found this on the internet so I throught I'd show all you people who have 2 strokes.Ĭhanging the power band of your dirt bike engine is simple when you know the basics.
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