Editing Multi-valve (section)

=== Alternative technologies ===

[[File:SUBARU EJ25 i-AVLS.jpg|thumb|Cutaway model of Subaru's [[Active Valve Control System|i-AVLS]] variable valve timing system on SOHC 4-valve-per-cylinder [[Subaru EJ engine|EJ25 boxer engine]] at Tokyo Motor Show 2007.]]
[[Turbocharging]] and [[Supercharger|supercharging]] are technologies that also improve engine breathing, and can be used instead of, or in conjunction with, multi-valve engines. The same applies to [[variable valve timing]] and [[variable-length intake manifold]]s. [[Rotary valve#Use in engine design|Rotary valves]] also offer improved engine breathing and high rev performance but these were never very successful. [[Cylinder head porting]], as part of [[engine tuning]], is also used to improve engine performance.