Overhead cam
|
|
Template:Reqimage Overhead cam (OHC) piston engines place the camshaft above the cylinder heads and drive the valves or lifters directly instead of using pushrods. This arrangement is more complex, and relies on a timing belt or chain, but allows for greater valvetrain flexibility. Currently, engines have used single overhead camshafts (SOHC) or dual overhead camshafts (DOHC), which refers to the number of camshafts per cylinder bank.
Many OHC engines today employ Variable Valve Timing and multiple valves to improve efficiency and power. OHC also allows for greater RPM, though pushrod designs have closed the gap somewhat.
The highest-revving automobile piston-engine currently available from a large-scale manufacturer is a DOHC design found in the Honda S2000 with a 9,000 RPM limit. Most production car engines with an OHC-controlled valvetrain have limits between 6000 and 7000 RPM. Honda achieves this unusually high rev-limit by use of lightweight components and techniques learned from their design of motorcycle engines.
In addition, purpose-built small-volume engines like the Powertec RPA V8 engine from Radical Motorsport can be built to higher specifications than mass-produced engines. The 2.6 L version has a 10,500 RPM limit and there is a de-stroked 2.0 L version planned that is said to have a 12,500 RPM limit.Template:Tech-stub