VE = volumetric efficiency (volumetrisk effektivitet på dansk)
hugget fra wikipedia:
http://en.wikipedia.org/wiki/Volumetric_efficiency
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Volumetric efficiency in internal combustion engine design refers to the efficiency with which the engine can move the charge into and out of the cylinders. More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%. Volumetric efficiencies can be improved in a number of ways, but most notably the size of the valve openings compared to the volume of the cylinder and streamlining the ports. Engines with higher volumetric efficiency will generally be able to run at higher RPM, and thus power, settings as they will lose less power to moving air in and out of the engine.
There are several standard ways to improve volumetric efficiency. A common approach for manufacturers is to use a larger number of valves, see multi-valve, which cover a greater area of the cylinder head. Carefully streamlining the ports increases flow capability. This is referred to as Porting and is done with the aid of an air flow bench for testing. Today, automobile engines typically have four valves per cylinder for this reason. Many high performance cars in the 1970s used carefully arranged air intakes and "tuned" exhaust systems to "push" air into and out of the cylinders through the intrinsic resonance of the system. Two-stroke engines take this concept even further with expansion chambers that returns the escaping air-fuel mixture back to the cylinder. A more modern technique, variable valve timing, attempts to address changes in volumetric efficiency with changes in RPM of the engine -- at higher RPM the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine.
More "radical" solutions include the sleeve valve design, in which the valves are replaced outright with a rotating sleeve around the piston, or alternately a rotating sleeve under the cylinder head. In this system the ports can be as large as necessary, up to that of the entire cylinder wall. However there is a practical upper limit due to the strength of the sleeve, at larger sizes the pressure inside the cylinder can "pop" the sleeve if the port is too large.
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En sugemotor kan med skrappe knaster (og et godt flow i topstykket) opnå et VE på over 100 i et meget smalt område, hvor hastigheden af luft/benzinblandingen og derved inertien har mulighed for at pakke luften i cylinderen lidt tættere end det atm. tryk der er uden for cylinderen
For at opnå et VE på over 100 skal udstødningssystemet også være optimeret således at foregående udstødningstakt har skabt et vacuum i den efterfølgende's "downtake runner" og dermed sørget for at cylinderen er blevet ordentligt tømt
(jeg ved ikke om man kan optimere så meget at det i et ultra lille vindue på ens rpm kurve er muligt at få tømt cylinderen så effektivt at der kan opstå et lille vacuum set i forhold til det atm. tryk)
En trykladet motor kan nemt opnå et VE på over 200% (1 atm. ladetryk hvilket svarre til 1 bars ladetryk, der er dog en lille forskel på atm og bar)
Hvilket også er hvorfor at det er så meget nemmere at få meget store effekter udaf en trykladet motor
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