4 valve per cylinder vs 2

[tkent02]

The way Suzuki did it, the valve components wear out much quicker with the four valve systems. With the two valve setup, all of the forces are in a straight line, pushing straight up and down. No pressure on the valve guides, no rockers to wear, no problems ever unless you let the valves get too tight.

With the four valve, there are twisting and bending forces on the valves, the valve guides wear out quicker, once the guides get loose everything up there starts to wear quicker.

I have never heard of a four valve Suzuki going over 100,000 miles without engine work, with the two valve designs it is routine.

True what Steve said about the potential to make power, but in the case of these old Suzukis, there's not much difference. A 1980 750 isn't noticeably faster than a 1979. A 1981 1100 is faster than a 1979 1000, but not by a whole lot.

[Steve]

Yes, four valves are generally better than two. Why? At low valve lift (let's pick the time valves are just opening or about to close, they are 1-2mm open), all the air must go through a slit that is 1-2mm high and as long as the circumference of the valve. In a 4-valve engine, although the valves themselves are smaller, the sum of the circumference of the two intake valves is greater than the circumference of the single intake valve of a 2-valve engine. That allows better breathing sooner in the cycle, then, the area opened up by two valves at higher lift is again larger than the area opened up by a single valve, so they breathe better at high lift, too.

As tatu mentioned, the four-valve engines have smaller, lighter valves. The lighter valves can allow higher engine speeds or more-radical cam profiles, either one of which will make more power.

Because of the better breathing, they have a flatter torque curve AND higher peak power, what's not to like?

About the only dis-advantage is that you have twice as many valves to keep adjusted.

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[tatu]

Which is better if all else is equal and why.

Someone recently asked me this and I didn't know what the complete answer was.

Looking for insight.

4 vlvs is better, more efficient burn, less inertial mass.

[Mekanix]

Which is better if all else is equal and why.

Someone recently asked me this and I didn't know what the complete answer was.

Looking for insight.