Valves.. Why?

[Chris Y]

Hi guys,

I know some of you are quite knowledgeable with engines (unlike me), so here's a question: Why are we still using valves?

I mean, engineers who modify cylinder heads for extra power love cutting back the castings where the valve guides go - for extra gas flow, and the general shape of the valves is so restrictive, and you need a 90 degree turn in the inlet/exhaust ports in most cases..

So, why not use something like a butterfly valve, like in a carb? Then, you could have the controls for the butterflies at the side of the head, and have straight-down ports, rather than 90 degree kinks. Also you'd get less restrictions in the ports.

The only downside is that I can't think of a decent way to control them from the cam.. Perhaps this is the reason we've stuck with valves for all this time..

What do you think? Would it be possible to use alternatives to 'normal' valves?

[KC]

The problem comes from combustion chamber sealing. the valve must be able to withstand the explosion of fuel and air and deal with the extreme heat, especially the exhaust valve. I don't think a butterfly valve could handle this without a major redisign. a lot of pure racing engines use a very narrow angle for the intake runner to make the mix a straighter shot into the combustion chamber. Also the valves are spiral ground on their back side to promote swirl in the chamber and fiurther mix the air and fuel. At least that is what we have done on our 502 cu. in. drag race engine. I would love to see self contained nitrogen springs used instead of mechanical springs because of their repeatability, but longevity has been an issue for anything more than race engines.

[Ray Bell]

Rotary valves have been used, sleeve valves have been used, but the poppet valve seems to be the only one that doesn't affect combustion chamber shape...