Octane rating

Well, When I bought my '02 MCS a few months ago I filled it up with regular, not knowing the octane requirements. It seemed to run fine, so I continued doing so. Then after reading an octane thread on sunshineminis.com, I made the switch to premium. Apparently, the computer will retard the timing if it senses any pinging. This will prevent damage to the engine, but will also result in lower performance and lower gas mileage. At least that's how I understood it.

Besides, with a 13 gallon tank, you're only talking about three bucks more per fill up, right?

What year/model is your car?

Charlie (dauph59)

TOM -

You didn't specify the Cooper or Cooper S.

While both specify "premium", the specs for the Cooper have an engine compression ratio of 10.6:1 while the Cooper S has 8.3:1.

I can't answer your question, but it seems to me that the S model ought to be better able to tolerate a lower octane fuel, if any model can. (On the theory that higher octane is needed for higher compression engines, to avoid "ping".) How can they both require the same premium fuel? I dunno. Compression ratio might not be the whole story. A quick look shows some cars with compression ratios of 9:1 only requiring 87 octane... Conventional wisdom says use the lowest (cheapest) gas that doesn't ping... but like dauph59 suggests, maybe these new-fangled computerized thingies mess up that old school method.

For me, the price difference in grades doesn't really matter - even if I drive 10,000 miles a year (I work from home) - I will only use 400 gallons of gas, assuming 25 mpg.

So for the 20 cent per gallon difference, that is only $80 a year (out of $1200+ at current prices). If you really drive a lot, and the 20 cents/gal matters, try it out - do a tank or two of regular and check your mileage, then do a couple of premium and see if there is an mpg difference.

Finally, I can't resist ;-) "Your mileage may vary..."

They will all run quite happily on the lower octane fuel, and the knock sensor on the engine should cause the computer (ECU) to adjust the engine accordingly to prevent pinking/pinging, Although the higher octane fuel is more expensive, it does make a noticeable difference in performance and economy, and would always be my choice, Fitzy

Charlie

I do not own a Mini but am considering it as a possible new car. However, when I read in the specifications that it used premium gas it made a quick dive to the bottom of the list. That is what has prompted my question.

TOM

TOM,

I drive close to 300 miles on a fill up (13 gallons), and that's mostly city driving with a heavy foot. Have you driven a MINI yet? I really think you should. It's a blast! It'll surely move up your list again, premium gas or not.

As far as the "S" having a lower compression ratio, but still needing the higher octane fuel, my understanding is that the compression needs to be lowered when a supercharger is used to keep the engine from developing too much pressure. (sorry for my non-technical answer, but I'm not that technical myself!)

Charlie

If thats a reason to bump it off your list then ffs don't buy one. Go and buy yourself something nice and sensible.

Just returned from France where I've been filling up with that Super Blue fuel at the carrefour petrol stations - f*ck me its rocket fuel !!