Forged pistons have higher thermal expansion as I recall, so the cold clearance must be larger. This will impose a larger load on the rings when the engine is hot. That is probably of no concern for a race car, but for a daily driven car it might be. Forged pistons are stronger, but this is needed only if very high rpm is to be obtained. I do not think you need them for a street engine. D^2 > I have seen on P.A.W cast and forged pistons > ok maby stupid to ask but what is the deverence in quality > also i find sometimes used pistons on ebay is that worth a try > while rebuilding I want to try to get some more power > and probably go for hardend valve seats