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An overhead valve engine, abbreviated (OHV) and sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead (or "sidevalve") engines , where the valves were located below the combustion chamber in the engine block .
An F-head engine combines features from both overhead-valve and flathead type engines, the inlet valve operating via pushrod and rocker arm and opening downward like an overhead valve engine, while the exhaust valve is offset from the cylinder and opens upward via an integrated pushrod/valve stem directly actuated by the camshaft, much like the ...
This reduces friction, uneven wear and "bell-mouthing" of the valve guide. [1] These allow higher engine speeds (RPMs) and higher loads, and were initially confined to high-performance and racing engines due to the considerable extra expense. Roller rockers can also be used in overhead cam engines (OHC). However, these generally have the roller ...
Initial compression ratio varied between 4.5:1 and 4.75:1 in different engines, with 77 bhp (57 kW), 90 bhp (67 kW) and 104 bhp (78 kW) for 221, 273 and 345 engines respectively; when the 320 engine was introduced, it produced 120 bhp (89 kW), increasing to 170 bhp (130 kW) later.
In other engine designs the camshaft is in the crankcase, in which case each cam usually contacts a push rod, which contacts a rocker arm that opens a valve, or in case of a flathead engine a push rod is not necessary. The overhead cam design typically allows higher engine speeds because it provides the most direct path between cam and valve.
A crossflow head gives better performance than a Reverse-flow cylinder head (though not as good as a uniflow), but the popular explanation put forward for this — that the gases do not have to change direction and hence are moved into and out of the cylinder more efficiently — is a simplification since there is no continuous flow because of valve opening and closing.
Engines with multiple banks are shorter than straight engines of the same size, and will often have better engine balance characteristics, resulting in reduced engine vibration and potentially higher maximum engine speeds. Most engines with four or less cylinders use a straight engine layout, and most engines with eight cylinders or more use a ...
Cutaway of a dual overhead camshaft engine 1969 AMC V8 overhead valve engine. The rocker cover has been removed, so the pushrods, rocker arms, valve springs, and valves are visible. A valvetrain is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. [1]