RX8Club.com - a way to get rid of valves?

Ok, so I know automotive forums like this tend to be the breeding ground for half-baked ideas on car technology, but I've been thinking about this one for a while.

Imagine a cam that doesn't have lobes, instead it has a rectangular slot cut thru it over the intake of the cylinder. Around each 'valve' there would basically be a solid cube. The bottom would be the 'valve' area, the top would be open to the intake/exhaust runner, the sides parallel to the 'cam' would have spring-mounted side-seals which would push against the side of the cam, and the other two sides would support 'side-seals', sealing the 'cube' along the axis of the 'cam'.

The cam would turn at 1/4 the engine speed. Air flows in thru the top of the cube, and can pass thru the cam when the slot is aligned correctly. The cam's rotation turns the slot so the openings are against the cube walls, effectively sealing off air flow. Exhaust would work the same, just opposite direction of flow. Basically its windows cut thru the cam's to replace having to open and close valves. Duration and 'lift' would be determined by the shape of the opening of the slots cut into the cam. The advantages here are no reciprocating parts, and no valve springs involved, which tend to float at higher rpms. This design should be able to support very high rpms.

The major question would be sealing, but essentially this is the same problem as is encoutered in the rotary engine. You're basically making some chambers along a common shaft and you want to seal them from each other. I'm not sure that seals would even be necessary if the tolerances were tight enough.

So has anyone heard of something like this? What disadvantages would there be? Sorry to post my probably half-cooked idea, but I can't find anything really wrong with it.