Discuss: Is there truly a benefit to 5 valve vs. 4 valve?
03-20-2003, 08:54 AM
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Discuss: Is there truly a benefit to 5 valve vs. 4 valve?
<a href="http://autozine.kyul.net/technical_school/engine/tech_engine_2.htm#3,%204,%205-valve" target="_blank">this article</a> doesn't think so.
03-20-2003, 10:15 AM
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The advantage is realized when a long stroke small bore engine......
are combined. It is difficult to get proper airflow when these two are combined. Most engines are large bore & short stroke. When using a large bore you have lots of room for larger valves. Thats when 5 valves are not needed. If you search for the orginal press info on the 1.8T you will find out that is why they went with the 5 valve setup.
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03-20-2003, 11:05 AM
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A few more points on the topic. --->
Torque and power are not the only criteria for breathing efficiency. Fuel economy and emission also play a role. Ideally, the valves should be able to open and close instantly to optimize volumetric efficiency with minimum spillage. That would require valve trains with zero inertia. But one can achieve faster valve motion with lighter (smaller) valves. Thus 5 smaller valves are better than 4 larger ones.
Some F1 engines lately use pneumatic valve actuation, driving the valves in both direction by air. I think they must have gone back to 4 valves because of real estate benefits from symmetrical actuator orientation.
Some F1 engines lately use pneumatic valve actuation, driving the valves in both direction by air. I think they must have gone back to 4 valves because of real estate benefits from symmetrical actuator orientation.