Why are 4 valves per cylinder better than 2 valves per cylinder? Is DOHC better than OHV? 4 valves per cylinder allows for more airflow than 2 valves per cylinder, as there is larger open area when the valves are open. Having a configuration with DOHC and four valves per cylinder means better airflow, especially at high engine speeds, resulting in better top end power. Though it is possible to run 4 valves per cylinder with a pushrod setup (OHV), it's far more common to run 2 valves due to the complication of the packaging requirements associated with a four valve setup.
The main advantages of a multi-valve head is that it allows for more airflow through greater coverage, placement of the spark plug in the center of the head for better flame propagation leading to greater efficiency, and it greatly reduces valve float at higher RPM through the use of smaller, lighter valves with less reciprocating inertia. With the prevention of valve float, engines can rev higher and produce more power.
The advantages of two valves per cylinder is a reduction of parts, thus saving cost and complexity. The design also tends to be better for low and mid range torque as the airflow is faster at these engine speeds as a result of a more restricted flow. Also, OHV engines allow for central placement of the camshaft within the V of V8 engines, meaning a smaller package and lower CG.
DOHC vs SOHC vs OHV - https://youtu.be/1GZtShToroc
HEMI Engine - https://youtu.be/qLns7ibeUps
VTEC - https://youtu.be/G6S4D14VS7w
3 Stage VTEC - https://youtu.be/Ol3nWQbatrQ
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