Editing Four-stroke engine (section)

=== Power output limitations ===
[[Image:Ciclo del motore 4T.svg|right|250px|thumb|The four-stroke cycle
<br>1=TDC
<br>2=BDC
<br><span style="margin:1px; background-color: #10ff00;">'''&nbsp;A: Intake&nbsp;'''</span>
<br><span style="margin:1px; background-color: #ffae21;">'''&nbsp;B: Compression&nbsp;'''</span>
<br><span style="margin:1px; background-color: #ff0000;">'''&nbsp;C: Power&nbsp;'''</span>
<br><span style="margin:1px; background-color: #639eff;">'''&nbsp;D: Exhaust&nbsp;'''</span>
]]

The maximum amount of power generated by an engine is determined by the maximum amount of air ingested. The amount of power generated by a piston engine is related to its size (cylinder volume), whether it is a [[two-stroke engine]] or four-stroke design, [[volumetric efficiency]], losses, air-to-fuel ratio, the [[calorific value]] of the fuel, oxygen content of the air and speed ([[revolutions per minute|RPM]]). The speed is ultimately limited by material strength and [[lubrication]]. Valves, pistons and [[connecting rod]]s suffer severe acceleration forces. At high engine speed, physical breakage and [[piston ring]] flutter can occur, resulting in power loss or even engine destruction. [[Piston ring]] flutter occurs when the rings oscillate vertically within the piston grooves they reside in. Ring flutter compromises the seal between the ring and the cylinder wall, which causes a loss of cylinder pressure and power. If an engine spins too quickly, valve springs cannot act quickly enough to close the valves. This is commonly referred to as '[[valve float]]', and it can result in piston to valve contact, severely damaging the engine. At high speeds the lubrication of piston cylinder wall interface tends to break down. This limits the piston speed for industrial engines to about 10&nbsp;m/s.

==== Intake/exhaust port flow ====
The output power of an engine is dependent on the ability of intake (air–fuel mixture) and exhaust matter to move quickly through valve ports, typically located in the [[cylinder head]]. To increase an engine's output power, irregularities in the intake and exhaust paths, such as casting flaws, can be removed, and, with the aid of an [[air flow bench]], the radii of valve port turns and [[valve seat]] configuration can be modified to reduce resistance. This process is called [[cylinder head porting|porting]], and it can be done by hand or with a [[CNC]] machine.