I'm not a scientist nor a mechanic so don't take it as the bible. This is just a general explanation.
Without getting too technical, knock is caused by premature detonation of fuel. Imagine your pistons going up and down. Fuel is "detonated" inside the piston chamber. If the fuel is detonated prematurely (e.g. not a full stroke) it will cause "knocking" because the timing is off. A higher octane fuel has a higher heat tolerance and will detonate at a higher temperature, and hence, allow the pistons to reach full stroke. However, with today's high tech cars, the car's computer can detect knocking and will adjust the cars setting (e.g. air/fuel mixture, etc.) to help reduce knocking.
So if you are getting knocking, then a higher octane fuel will retard the knocking. I think one of the causes of knocking is engine sludge. My recommendation is to fill up with Chevron fuel. The Techroline additive is good at keeping your engine clean. Once in a while, if you want to give it a good clean you can buy a bottle of Techroline additive and add it with your fill-up.
I've got a '92 Talon Tsi, and the recommended fuel is premium unleaded (91 octane). With cost of gas being so high, I tried 87 octane to see what the difference was. I didn't experience knocking, but I did notice a slight performance decline. I believe this is because the computer detected lower octane/knocking and will adjust accordingly (e.g. lower performance to reduce heat).
Hope this helps,
Stan Quan
