Originally Posted by Chip

Well not really, as they have little experience of specific engines in reality, so its a case of tuners being able to give them enough information to work with, and even then its only ever going to be in the right ballpark rather than anywhere near as finely optimised as manufacturer cams are.

For turbo use, cams are less of an issue (dont get me wrong I am NOT saying they dont matter) as they arent the only very drastic factor shaping the engines performance like they are with N/A (again dont think that means portwork or compression ratios etc arent important, they are, but they wont make the dramatic effect a cam change will)

And of course manufacturers have to be obsessive about economy and emissions, aftermarket tuners need to consider these, but not to the same extent.