I know this may be a silly question to ask, but what kind of reliability hit should one expect when pushing +100-200 HP over stock? For example, if the N55 lasts on 100k miles on average before major problems, after tuning, should I expect the lifetime of the engine to go down significantly, perhaps to 50k miles? Even less? I'm just trying to get a sense of how much damage I'll be doing to my wallet
On the other hand, if you only increase torque slightly, but allow the top end to breathe easier with a big turbo and increased fueling (preventing the torque drop off after 6k RPM) for higher top-end HP, I don't think that should effect reliability too much, right?
I see that some of the companies listed above claim "OEM reliability", but that's probably referring to the turbo only, and not the system as a whole.