Triple valve engines - 2 valves in or out?

[FunkyNige]

I know I'ma bit of a numpty when it comes to all things technical, but I am trying to learn...

I was thinking the other day about triple valve engines and I can't figure out whether it's best to have one intake and two exhaust valves, or the other way round.
What do car manufacturers generally go for?

[Mr2Mike]

The greatest valve area is ALWAYS required on the inlet side. On a normaly aspirated engine, the only thing pushing the air into the cylinder is atmospheric pressure. OTOH, during the exhaust stroke, the engine is pushing the exhaust gasses out of the cylinder, so a smaller valve will suffice.

With triple valve engines, there is always two inlets and one exhaust.

[cymtriks]

An exception springs to mind. There's always one. Vintage Bugattis had one inlet and two exhaust valves. The main performance limitation was overheating of the exhaust valves and two exhausts ran cooler than one. Getting air an fuel in through one inlet wasn't a problem as the engine could be equipped with a supercharger.

[350zwelgje]

Just a small addition: 2 valves in yes, but the one out is most of the times larger in diameter. The design is still to allow maximum flow, even when the cilinder pressure is helping the out flow.

Rob