I'm not trying to argue with you here, but I'm about 99% positive that statement is inaccurate. Ford EEC-IV systems from '84 to '95, for example, were OBD1 and they did self-learn, and the multipliers in the programming allowed a good deal more adjustability than I think you're giving credit for...and we're talking changes as big as cams, heads, intakes, exhaust--all on the stock computer (trust me-thousands of people myself included have done it--and I had a completely different induction, cam, and exhaust). Did you have to do some other tweaking (fuel pressure adjustment, timing, idle throttle setting, etc) sometimes? Yes, but unless you were putting on nitrous or forced induction or running a cam that significantly changed the intake flow signature, the stock or even an aftermarket MAF, would make it's own adjustments. Now, granted that's a Ford system, and not a Pentastar or GM, but by the time the EEC-IV came out in 1984 or '85 (can't recall clearly right now), all the big three and every other make were utilizing similar technologies which could account for a decent amount of variability. If you're talking about a multiport system from the late 80s, I'm all but completely positive your computer can account for some modest performance upgrades to include a free flowing exhaust without having to remap your computer programming.