So I was reading Jetswing's poll, and a coupla ppl mentioned wanting 4 valves per cylinder. Which made me ask myself, why? I know alot of the bigger bikes have 4 or more valves per cylinder, but to what end? Higher compression? More power or somethin? Better efficiency in engine size to power? Just curious really...

Better breathing (not you, the bike).

If done correctly it would provide more power over a wider range.

The more air an engine can move, the more power potential it has. Four small valves can move more air than two big ones.

It is interesting to note that the Ninja 500r (yes, even the Ninja 250r) has 4 valves per cylinder.

Quote from: PhaedrusIt is interesting to note that the Ninja 500r (yes, even the Ninja 250r) has 4 valves per cylinder.

The Hyosung GT250 Comet (the AlphaSports bike that uses the GS500 frame) has a 4-valve-per head, too.

Suzuki is really the only company that still runs an entry level 2-valve motor.  They have no reason to upgrade.  It's a simpler, cheaper assembly.

Quote from: PhaedrusIt is interesting to note that the Ninja 500r (yes, even the Ninja 250r) has 4 valves per cylinder.

And, the 250 has a 14,000rpm redline, which means that one piston is travelling in the area of 500mph and has to instantly go in the other direction on the next stroke.

I like only having to check 4 valves.

Quote from: PhaedrusIt is interesting to note that the Ninja 500r (yes, even the Ninja 250r) has 4 valves per cylinder.

It's also water cooled.

So, would I be correct to assume:

1) The reason the Ninja has a high speed advantage over the GS is because it has 4 valves per cylinder MORE SO than because of the liquid cooling and higher displacement?

2) The GS is also known more for it's reliability over the Ninja, despite the liquid cooling of the Kawi. Could what scratch have said have something to do with the increased realiability of the GS engine?

From http://www.gstwins.com/forum/viewtopic.php?p=197596#197596

Quote from: AlphaFire X5

Quote from: aevans17(The increase in power band is most noticable at the higher RPM's, and is largely due to the increased engine size. Yes the ninja is also liquid cooled, but that can be bad because that adds one more failure point.)

Actually, the increase in power in the Ninja 500 in the upper rev range is mainly due to the fact that it is a 4-valve-per-cylinder engine. 12cc displacement advantage is not really all that, especially not 11HP worth. If 12cc produced a net result of 11 HP, we'd have 1000HP liter bikes.

Alphafire.

So which would actually be more powerful (all other factors being equal)

...a 4 valve per cylinder engine?

or..

...a 2 valve per cylinder engine bored out?

:dunno:

<-- internal engine noob

Quote from: PhaedrusSo, would I be correct to assume:

1) The reason the Ninja has a high speed advantage over the GS is because it has 4 valves per cylinder MORE SO than because of the liquid cooling and higher displacement?

2) The GS is also known more for it's reliability over the Ninja, despite the liquid cooling of the Kawi. Could what scratch have said have something to do with the increased realiability of the GS engine?

The power advantage is a combination of things...including the four valves, displacement and watercooling (worth a 25% gain in power right there).

Quote from: Phaedrus Alphafire.

So which would actually be more powerful (all other factors being equal)

...a 4 valve per cylinder engine?

or..

...a 2 valve per cylinder engine bored out?

:dunno:

<-- internal engine noob

That can only be given blanket answers.  A 4-valve, watercooled 500cc engine isn't going to be able to match the efficiency of a oil cooled 2-valver 500 bored/stroked to 650cc...

Quote from: makenzie71The power advantage is a combination of things...including the four valves, displacement and watercooling (worth a 25% gain in power right there).

Your 25% gain would be in combustion chamber shape and the number of valves for better flow. Liquid-cooling allows the use of a higher compression chamber without distortion of the metals.

Quote from: makenzie71A 4-valve, watercooled 500cc engine isn't going to be able to match the efficiency of a oil cooled 2-valver 500 bored/stroked to 650cc...

Efficiency? Explain, please.

Quote from: scratchYour 25% gain would be in combustion chamber shape and the number of valves for better flow.

the motor handles the enhanced combustion and flow characteristics more efficiently because of water cooling.  We wouldn't be seeing near the reliable power output we do today without it.

As Scratch said, water cooling allows for greater power production, it does not induce it.  

Water cooling simply allows the cylinder walls to shed more heat.  Water cooling is also capable of buffering the cylinder wall temperatures for short periods of time by providing increased thermal mass.  Another benefit is that water cools more evenly than a poorly designed air-cooled scheme.

That said, a well thought-out air-cooled engine is perfectly capable of just as much power per cubic inch as a water-cooled engine.  You just need more airflow, and more even distribution.  This is why aircraft engines have very complex baffling schemes.  It's also why the cylinders look like porcupines with all their fins.

The reason for four valves is geometry.  4 valves provide more valve area than 2.

Keep in mind that smaller valves are also less prone to failure than large valves.

The total area of the small circles is the same:

There are a couple of additional advantages of 4-valve heads....

The spark plug is placed in the center of the combustion chamber. This provides a more even and complete burn. Thus more power.

The valves and springs are smaller individually. This means they are lighter. This allows for higher reving before valve float. Which equates to more power.


Tolerances can be tighter on a liquid cooled motor. Air cooled motors have to have greater tolerances to survive. This "slop" relates to loss of potential power.

dgyver - Does the fact that the EX500 is rocker vs. shim make any difference?

Thanks

Quote from: Onidgyver - Does the fact that the EX500 is rocker vs. shim make any difference?

Thanks

Not really...the rockers on the EX500 are heavy and complicated...just more rotational mass.  Only advantage is that they're easier to adjust.