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So, I ignored everyones advice....

P

Plugers

Senior member
Hope my wallet doesn't hate me.

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ThatsABigOne said:
40 valves? So that is 5 valves per cylinder. 2 intakes and 3 exhaust? or vice versa?
Click to expand...

3 intake 2 exhaust.

Intake area is always greater than exhaust on any head. Even with same # of valves the intake valves are bigger.

Heres why:

Pulling air into the cylinder relies on vacuum, or more precisely 14.7 psi of atmospheric pressure when the piston is traveling down.

The piston travelling upward is capable of creating over 150 psi depending on compression ratio. Over a factor of 10 more than intake and that's the minimum with a low compression engine around 8:1.

It's harder to get gases into the cylinder than out and for that reason alone valve surface area is always biased towards intake regardless of number of valves. Even if the 3 intake valves are slightly smaller than 2 larger exhaust valves, it still adds up to geometrically greater flow area on the intake side.

Exhaust also helps in part to expel itself in that it's still energetic and expanding at greater than atmospheric pressure when the exhaust valves open to atmosphere, thus exhaust gas would start flowing out on it's own even if the piston was stuck at BDC and wasn't moving at all. Intake isn't going to do that without a blower or turbo :awe:
 
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