But what about the NON-turbo Mini?
 

I have no problem with the requirement for premium gas in the forced induction engines.
The answer I am seeking is why premium (or even mid-grade (89 octane), really!) is a requirement for the standard Mini without a turbo or supercharger, unless the compression ratio is 10:1 or more in that engine.
So, can anyone state (with certainty) what the ratio actually IS? (and in this case you DO know what "is" means, Bill!) :)
And at the Chevron station where I buy my gas, premium (93 octane) is 30 cents a gallon more than regular (87 octane).
No, I'm not pursuing false economy at the expense of damaging an engine. Our 1981 Porsche 911 SC ran just fine on 89 octane as did our 1998 BMW Z3.
Since here in east central Florida, it is not unusual for a weekend days drive to hit 150-200 miles or more, when the price of gas goes nuts again (remember the $4.00/gallon for regular gas not so long ago? And premium grades were not even available for periods of time) it could well be a matter of having to restrict driving more than we really want to.
But really folks, since we are still in the purchase decision phase of which Mini (Standard versus "S") or the new Honda CRZ (for long term reliability), this is more a matter of becoming an informed consumer.
BTW, you should see what the J.D. Powers survey of Mini owners (available on the Carfax reports) says about the build quality and reliability of ALL Minis! :( THAT will probably go over like a fart in church! :)
Bob

well I do not know if you have gen1 or 2. regardless find the specs and use this site
http://www.csgnetwork.com/compcalc.html
or get a compression tester and measure yourself. BMW tend to use high compression

as to your imperial data on using mid grade regular gas for a car rated for premium

IS there proof you did not damage your car and decrease its lifespan? (and in this case you DO know what "is" means, Bill!)

Got my answer
 

T-bone and the group,
First, we don't as yet OWN a Mini.
Yesterday we went to Orlando Mini and I had a (VERY hot!) female sales person get an owners manual from a new car so I could read what it said about fuel grades. Here is what Mini says about fuel: While they strongly recommend 91 octane for ALL Minis, they DO allow the use of 89 octane in the "S" and the JCW, and 87 octane in the standard Mini, acknowledging that some spark knock WILL occur which they say will NOT harm the engine.
Given that, I would have to see with my own eyes that a non-turbo Mini has trouble running on 89 octane before I would be convinced, given this statement from the company that builds the car.
We also visited a Honda dealer who has a new CRZ tricked out with all of the goodies. It looks considerably better than the stock one (especially with the rear spoiler and some pin striping), and can be had for around $28,500 or so.
Since we are coming to the conclusion that we would have to special order a new Mini to get what we really want in a new one, I am haunting the Auto Trader and Craigs List sites in hopes of finding that car as a clean late model used.
Bob