5 valves per cylinder... 2 intake, 3 exhaust? What's the benefit of 5 valves vs. 2 or 4?
03-30-2001, 08:16 AM
#3
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Switch it...3intake, 2 exhaust. Exhaust gases move faster than intake thus requiring...
less total valve area. Overall more valve area allow for the engine(giant air pump) to move air quicker and easier. Sometimes many smaller valves gives a greater overall valve area than say two larger valves. For example on a 2in diameter valve the area is pi*(1^2)=3.14159sqin., but two 1.5in valves(assuming they fit) will have a valve area of 3.53sqin. This can be applied to most anything including exhaust piping, sometimes two smaller pipes flow just as good or better than one garbage can sized one.
03-30-2001, 08:16 AM
#4
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it's 3 in, 2 out...
It is arguable whether 5 valves per cylinder helps raise engine efficiency. Audi claims it does, but has failed to provide evidence to support this claim. In fact, its 5V engines are no more powerful and torquey than its German rivals with 4 valves per cylinder.
Originally, 5-valve design didn't guarantee covering more head area than a 4-valver. Nevertheless, if the head of combustion chamber is in an irregular shape , the valves may cover larger area. The Ferrari 355 make use of this to enhance high-speed breathing. Yet the disadvantage is that faster breathing also harms low-speed torque if no counter measure is taken.
All existing 5-valve engines have 3 intake valves and 2 exhaust valves per cylinder, arranged as a cross-flow system. The exhaust valves are large, but in terms of total area intake valves are larger. In the 355, by arranging the outer intake valves open 10 degrees earlier than the center valve, it allows for the swirl needed for better air / fuel mixture, hence more efficient burning and cleaner emission.
The advantage of 5-valve engine is still under scrutiny. Not only do few car makers use it (VW group, Ferrari and Bugatti), but Formula One cars also no longer favor it. Even the Ferrari F1 cars which were once famous for their 5V engine switched back to a 4-valve design a few years ago.
Originally, 5-valve design didn't guarantee covering more head area than a 4-valver. Nevertheless, if the head of combustion chamber is in an irregular shape , the valves may cover larger area. The Ferrari 355 make use of this to enhance high-speed breathing. Yet the disadvantage is that faster breathing also harms low-speed torque if no counter measure is taken.
All existing 5-valve engines have 3 intake valves and 2 exhaust valves per cylinder, arranged as a cross-flow system. The exhaust valves are large, but in terms of total area intake valves are larger. In the 355, by arranging the outer intake valves open 10 degrees earlier than the center valve, it allows for the swirl needed for better air / fuel mixture, hence more efficient burning and cleaner emission.
The advantage of 5-valve engine is still under scrutiny. Not only do few car makers use it (VW group, Ferrari and Bugatti), but Formula One cars also no longer favor it. Even the Ferrari F1 cars which were once famous for their 5V engine switched back to a 4-valve design a few years ago.
03-30-2001, 08:38 AM
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Engine speed is also helped
In the early '60s when Honda came to Grand Prix racing (bikes), the four valve head was used not only to give more valve area for more flow, but many little valves are lighter in individual weight, and thus accelerate faster/close quicker/can use lighter, more durable valve springs, etc., and just generally pound around less in the process. Meant higher redlines.
