I have an M50 engine on my 93 525i. I don't drive like a race car driver, maybe that is the reason why I don't notice any change in the way the engine runs. Of course here in California, the highest octane that one can get is a 92. So far, my car is back on the premium gas (92) and so far it is still running the same.
Do I need to change the chip. BTW, I found some on Ebay that they are selling very less.