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. 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. A colorized automobile engine An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... Design as a process can take many forms depending on the object being designed and the individual or individuals participating. ... A piston and cylinder from a steam engine A cylinder in an internal combustion engine is the space within which a piston travels. ... rpm or RPM may mean: revolutions per minute RPM Package Manager (originally called Red Hat Package Manager) RPM (movie) RPM (band), a Brazilian rock band RPM (magazine), a former Canadian music industry magazine In firearms, Rounds Per Minute: how many shots an automatic weapon can fire in one minute On...

There are several "standard" ways to improve volumetric efficiency. The most common is to use a larger number of valves, see multi-valve, which cover a greater area of the cylinder head. Today, automobile engines typically have 4 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 due to airflow over the engine. 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. poppet valve A poppet valve is the type of valve system used in most piston engines, used to seal the intake and exhaust ports. ... In automotive engineering, an engine is referred to as multi-valve (or multivalve) when each cylinder has more than two valves. ... This article provides extensive lists of events and significant personalities of the 1970s. ... Variable valve timing, or VVT, is a generic term for an automobile piston engine technology. ...

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 cyclinder 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. Sleeve valves are a way of building valves for piston engines that have a number of advantages over the more common poppet valve, used in most engines, as well as disadvantages that have precluded their widespread adoption. ...

See also

• engine tuning
• supercharger
• turbocharger