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So I've just been on a 200 mile jaunt around the Yorkshire countryside in the E21. Lots of twisty roads and hills - great driving!

I did notice slight overheating on hills and a lack of power though. On the way home I filled up with some premium high octane and I don't know if it was just mental but the car felt WAY better, sounded better and didn't seem to overheat. Previously I was shifting into lower gears to bring the revs up and heat down on long hills but didn't seem to need this on premium.

Am I definitely experiencing pre ignition/detonation here?

Can anyone explain to me what is happening and which way I need to twist my dizzy for better running on standard?

To get the dizzy right you need a timing strobe. I have one in my garage that I have no need whatsoever for any more. I'll stick it in the car and you can come and get it off me tomorrow if you like.

Thanks for the offer Jim. I have a timing light and timing is bob on at the minute - set it a couple of months ago.

I guess I'm asking if I should advance/retard timing and by how many degrees to compensate for modern low octane fuel? Or should I stick with premium?

It's the colder air and you sticking higher octane helped?