Excuse my ignorance, but I find this thread fascinating. Why are they so different. Engines designed and built in the 2000's are far better than 1960's. If I got 100,000 miles out of my 64 Fairmont I thought I had done well. Not much better in 78. Had to rebuild my 302 after 60,000 miles ( 100,000 KM ) Now I expect double to triple that ( 200,000 - 300,000) Km out of any vehicle. My XL Fairmont did not use oil and had no rattles at 270,000 KM. But all of a sudden Ford has gone back to the sixties. Slapped on a turbo and tolerances are any one's guess. This is a serious question - Why do engines vary to the extent reported in all these posts. I would have thought that a standard engine built to todays tolerances and reliability would all react the same to a tune. Obviously I am wrong - but why. Thanks all