Aha, ok. That makes things a bit clearer to me. Obvious why turbo = no overlap and with supercharging some is good.

But still a question arises to me: As I thought -and you explaned- when charging it's good to have larger exhaust then intake valves. You say "with turbo charged enines the ratio of pressure on the exhaust side vs pressure on the inlet side can be as bad as 2:1" So increasing outlet valve size would be a good thing. But why is this so? Is it only because of the somewhat smaller exhaust valve and port? I could imagine because of the turbo, the exhaust flow is restriced even more. But then again, that is not the case on supercharged engines. Thinking this over I would say that when using a belt driven charger you would indeed need somewhat bigger exhaust valves, but when using a turbo you'll need heaps bigger exhaust valves because of even more presure in the exhaust side. (or would valve size not matter because of the restriction due to the turbo then?)

Thanks again, Ben
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Volvo P130, 1965: B18A + tilted M47. Volvo P131, 1969: B20 + AW71L: in the proces of rebuilding (www.knutselsmurf.web1000.com)