I have an '88 m3 & have removed the cats,( still retaining the lambda sensor), and was wondering what grade of fuel you guys run? here in the uk we have a choice of premium unleaded (95 octane ) super unleaded (97 octane) or lead replacement petrol (not sure of the rating). I currently use premium unleaded as it's a lot cheaper , but was wondering if switching to a higher octane rating offers any performance advantage?, or is it just a waste of money? thanks for any help/ advice. Darren.