blaze4eva: I just thought you should know that NASCAR engines (I still think NASCAR is boring) do indeed rev to nearly 9000 rpm as do the top fuel dragster engines. To do that they need some seriously stiff valve springs and a lightweight valve train. Not to be mean but, you got your port velocity thing backwards too. A two-valve/cylinder engine has less flow area than a four-valve/cylinder engine (when comparing engines of similar bores). This results in HIGHER velocity through the intake port (vs the 4-valve motor). This aids cylinder filling at lower rpms but is a larger pressure drop across the valve at higher rpm resulting in greater pumping losses. The four-valve/cylinder engine experiences fewer pumping losses because of the smaller pressure drop across the valves. There is the main reason why a similar two-valve/cylinder engine will produce more low-end torque than a four-valve/cylinder engine but will not rev as high, and more than likely produce less peak power.