I have a 1986 535i with 170k miles on it. I just got a major tune-up and it runs great. Yet I want some more performance out of it. Which is the best chip available for a car with this many miles? I don't want to affect reliablity, but want the most I can get out of my car w/o hurting it! I don't want to do any engine mods now...I just want a GOOD chip for it. Your opinions will be helpful!