`Whats the difference between "cast" and "forged" pistons performance wise? Any advantages of running one over the other? And in older motors is it really necesary to convert to "unleaded" valve seats?
Forged pistons are stronger but heavier . They also hold up to detonation better and they warp lees from heat . Cast alloy pistons are fine for normal use but can fail under heavy mods. As for valve seats You could change them out or use a better quality valve . But unless you plan on not ever going back into your top end and riding around the world , the stock seats should be fine if you are worried add some desiel or lead additive to your gas . I have racked up thousand of miles on old british bikes that had stock seats and all I had to do was dress the seats when I changed out the rings and decarboned the piston crowns . Not a big deal at all !