Chungster wrote: Mon Dec 31, 2018 1:44 pm
Filling up with BP Ultimate 97 now which seems to have helped the mpg a bit.
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I wouldn't waste your money buying higher octane fuel - Your car can't take advantage of it and isn't set up for it.
Higher octane fuel isn't appreciably.more calorific than regular RON95 (it's a common misconception that it is), but the additives such as Toluene, Ethanol, MMT and TMB reduce the volatility of the fuel, allowing it to be compressed further without self igniting (pinking).
If your engine isn't set up to run on higher octane, it won't compress it further on advanced timing. Your 1.0TSI does not run on a higher compression ratio to take advantage of higher octane (97-99) fuels, the Polo and Golf GTI 2.0TSI units don't either - the Golf R/Seat Leon Cupra/Audi S3 are optimised for high octane fuels.
If you run on higher Octane fuels you won't do any damage, but you are literally chucking money away and might actually see lower mpg as a result - lower volatility fuel ignited by a spark in a low compression ratio engine may not combust fully - that may be a problem for cars with a GPF - that GPF will be loaded for longer if your engine is chucking out I'm completely burned fuel as more soot than is expected. Loaded particulate filters increase back pressure and lower mpg.
If you think you're seeing a.modest increase on mpg then it's probably running in gains, a change in your commute (less traffic on the roads in the weeks leading up to Christmas has seen my mpg go up over the last 3 weeks) or the placebo affect because you think that RON97 fuel is more calorific (Ethanol is about 10% less calorific than petrol, and is a common RON enhancer).