Noob Fuel Question!

Originally Posted by Xan

Kannibul basically has everything covered.

The only things I can add is, on top of fuel not always being exactly as posted, hot outside temperatures could also induce knock and have your ecu retard timing.
Although the inlet air temp map will most likely be retarding the timing to prevent this, higher octane fuel could help here to reduce that effect.

Also certain types of molecules that mid and regular fuels contain do not exist in premium fuel, therefore premium fuels leave less deposits.

Finally as all major companies have their own additives to prevent build up, but in their process build up themselves, it can't hurt to switch brands every 3000 miles or so.
(although some companies buy their additives from others, so it won't work then)
The principle behind this is that one brands additive will remove the other and switching prevents maximum build up.
(I don't have any prove of this, maybe someone else has seen research on this? But it makes sense to my and it can't hurt)