Owen Emry wrote: >No, sorry. No offense intended, but completely incorrect. Heptane (i.e., the rest of the fuel) contains more chemical energy than Octane, so the higher the octane, the less chemical energy per unit mass. > Hi Owen Thanks for the correctoin - I've learnt a bit more today! Basically what this means is that the slower burn allowed by a higher octane fuel results in being able to cram disproportionately more fuel into the cylinders. Makes sense, and tells me that the adverts telling us to buy optimax because it gives more power is basically rubbish - correct? (Optimax over here is 98 as opposed to 95 for unleaded - although we have a different measuring system) Martin To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/