I should know this by now, but I never really paid much attention to how oil weight can affect hp. I saw a commercial for royal purple saying their light-weight synthetics can improve hp, supposedly by lowering the mass the oil pump has to churn. I'm running a synthetic 20W-50 right now...should I go lower? How low is too low? It's getting time to change the oil and plugs so I figured I'd figure this out before I bought a load of oil.