2V vs. 4V

[85MustGT]

First of all I know the 4 cam engine makes more power but why?
Seems all the extra valves and cams would slow the engine down, I trying to make sense of this?

 

[crew_dawg16]

If you have a cylinder head that has 2 valves, you are limited to how big the diameter of those valve can be by the width of the combustion chamber. If you put 4 valves in a head, you can now have 2 smaller intake and 2 smaller exhaust valves that add up to a bigger overall area. This allows you to flow much more air at higher rpms.

 

[Dr. Wu 2000]

Both the 2v and 4v modulars love to rev, but the 4v really shines at higher rpm's, where the 2v's run out of breath, so to speak.

 

[hexum311]

More valves = more flow = more power.

article quote:
"Usually, double overhead cams are used on engines with four or more valves per cylinder. A single camshaft simply cannot fit enough cam lobes to actuate(operate) all of those valves"

http://www.streetracersonline.com/articles/camshafts/2.php

 

[Rocketman]

Short answer, because the 4v flows more air, which equals more HP.

Long answer: This is right out of the book.
The 4v engine does not require as much valve lift to achieve high flow rates, because the valve curtain area of the valve is the limiting factor to flow. The curtain area of a 4v design is much larger at lower vale lifts than a similar 2v design. A single intake valve would require a valve lift of .821 inches to match the valve curtain area of the 2 smaller intake valves in a 4v design with only .500 inches of lift.
Valve curtain area comparison:
4 valve head with two 37MM diameter intake valves with .500 inch of lift equals a valve curtain area of 4.57 square inches.
2 valve head with one 45MM diameter intake valve with .821 inch of lift equals a valve curtain area of 4.57 square inches.
This is the advantage a 4v head has over a 2v. To achieve over .800 inches of lift on a 2v design requires some very exotic valvetrain components, where achieving a similar flow potential with a 4v head can be achieved using mostly production pieces.

 

[CatmanJJ]

Like these guys said. Also if you ever have gone from a 2v SOHC GT to a DOHC 4v you'll immediatly notice a huge difference up top. Right when the 2v starts to run outta air and start weezing is where the 4v really starts to shine I think, up top around 6000 rpms.