I know, ultimately the answer is to tune on a dyno. But I would like to know what the reasons are for advancing/retarding intake/exhaust cam timing. Specifically with regards to different engine setups. For example I know for turbo setups, less overlap is better so in theory one would want to advance the exhaust and retard the intake. But in what situation would you advance both? What about NA setups, what is the goal, more overlap?