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BASIC ENGINE OPERATION
There are two basic types of gasoline-powered piston engines: Four-stroke and two-stroke.
FOUR-STROKE ENGINES
This most common type of engine, found in cars,
trucks and many motorcycles, goes through four
“strokes” or “cycles” of operation:
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2
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1. Intake
As the piston moves downward, the intake valve
opens, and a mixture of air and gasoline vapor (air/
fuel) is sucked into the cylinder.
2. Compression
As the piston reaches its lowest point (bottom dead
center) and then moves back upward, the intake
valve closes, and the air/fuel mixture is compressed.
3. Power
When the piston is near the top of its travel (top
dead center), the spark plug “fires,” which ignites the
air/fuel mixture. The pressure from the burning fuel
forces the piston downward.
4. Exhaust
As the piston then moves back upward, the exhaust
valve opens, and the burnt gases are pushed out of
the cylinder. The cycles then repeat.
Four-Stroke Engine Advantages:
Durable and efficient. Can be tuned for a combination
of high power, low fuel consumption and low emissions.
Four-Stroke Engine Disadvantages:
Requires complex control systems to produce the
optimal combination of power, fuel consumption
and emissions.
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