Good points, although I think the "compression ratio vs. octane requirement" chart is wayyyyy oversimplified. Static compression ratio doesn't determine octane requirements. Dynamic cylinder pressure determines octane requirements. Cylinder pressure can vary wildly depending on things like camshaft overlap, restrictions in the air inlet path, supercharging/turbocharging, engine temperature, air/fuel temperature, and a bunch of other factors.

Also, even though a particular engine might be able to "use" more than a certain octane rating, unless the computer can adjust the ignition settings (or you can adjust it yourself), you won't get any benefits. I have a Ducati motorcycle with 11.5:1 static compression. It runs fine with 93 octane, and I could probably get more power out of it with 100 octane if I wanted to, but it would mean manually adjusting the timing depending on what type of gas I had in the tank on any given day.

And since there's only one gas station around here that has 100-octane unleaded, I'm not inclined to use that for the default tuning settings on my bike.

Scott

 

There is no fixed compression vs octane requirement table. It can't be made. Tons of stuff go into combustion chamber design that will have a huge effect on detonation. Here's an example.... The new BMW twin turbo 6 has compression over 10:1, runs 7-9 lbs of boost, and does it on pump (91) gas. That couldn't have been done until very recently.... So disregard any information you have on boost and compression and octane for cars, unless you are working on a car from the same era as your literature.

And the Mini doesn't understand octane at all. It understands knock. DOesn't matter what the octane is. The Mini (or any knock sensor supervised motor) will only benefit from more octane until the eCU stops advanceing timing. Look at timing data from WOT runs and you'll see that for most tunes, going much above 95 or so doesn't really gain you anything.... Maybe it could, but you'd have to change your tune.

If I put the sweet stuff into my tank, my milage goes up by >10%. For $3 premium, I'd have to save more than 30 cents a gallon to get the same distance, with worse performance. Doens't seen like much savings to me. Not only do you loose power when the timing is pulled, but efficiency goes down the toilette to! I think that those that advocate using lower octane gas to save money hav n't really looked at the change in gas milage they were getting, or maybe they never live on the higher number side of the tach!

Matt

 

hey fantastic points you two

that combined with the article would give someone a perfect idea of what they should be running. it does seem that 95 or a couple of tic's higher might be optimal.

i guess 93 vpower is what I will be using on a regular basis. I had this idea of filling up with 3 gallons of 100 octane (we have it here, cam2) and then driving a half mile and topping it off with 93 vpower. The gas prices are falling so fast that vpower looks like regular. I calculated my monthly bills based up on milage ratings fairly accurately. There isnt a huge difference in gas cost, but it starts to show if I do the 100 octane for 3 gallons scenario.

Sunoco used to have 94 octane at all pumps, too bad its not around anymore. My camaro loved that stuff. I guess 93 vpower is the best out now besides maybe Chevron which doesnt exist in NY.

I read on Shell.com that vpower can be from 90-93 depending on state. I think actually it is 91-93, I never have seen a state where max octane was 90 so far.

Oxygenates are another confusing issue. Cam2 has less than 10%. Some say this is bad, some say this is good. Some hate ethanol, some say its the oxygenate now. I have no idea which is what, but it doesnt appear there is a choice in the matter unless you buy things like CAM2 and stuff.

 

I've read that if you live in high altitudes you don't need to put high octane in cars with high compression. You won't gain any advantage. However, I don't know if this changes when you slap on a supercharger.

 

but it all depends on the motor. The higher altitude means the air density is lower. All this ends up with lower charge temps under compression. With a blower, you're stuffing more air in for sure, even at higher altitudes..... But it all depends on engine design and control as to the effect on octane demand.

But if you use this as a way to build a hotter motor that doesn't knock, never drive down to sea level!

Matt

 

The car can use more than the 93 octane so this isnt much of an issue, being that nothing else is higher at your average non-racing gaseteria

i can see if you had a 1990 cavalier or something dingy like that, maybe then it wouldnt enjoy 93 octane at high elevations.

 

This is a pretty clear explanation of why.

http://www.bajajusa.com/High%20Octane.htm

 

Yes that article speaks mostly the truth, enough of it at least.

Unfortunately, car dealers and manufacturers lie about OPTIMAL octane levels for a car in order to not scare away people.

Penny wise and pound foolish is the assumption of any smart corporation today. People complain about the cost of bread and then put 2k down on a new car with 8% interest for 5 years. Have to get a clear perspective and find out what your car can use to its ultimate benefit (and performance)

 

I think it's funny that we won't blink at paying $1.25 US for a 500 ml (16.9 ounce) bottle water, but complain about paying for Premium.

 

That's the truth right there. The amount of electricity that people burn using this to decide was more money than the upgrade in gas.

 

The last few years my wife was driving an E430 Sport Benz which specifically states Premium (91 octane or higher) only. The dealership told us to run mid-grade during the winter since all northern market winter mixes are crap anyway. I never did, but I wonder how the detergent levels and performance are impacted when the winter mix is introducted. I know that my MPG always drops off 5 to 10%, but have never closely monitored the performance. With my new baby due to arrive in two weeks and winter mix close behind, I may get a chance to find out.

 

I guess that Octane of premium gas differs from country to country.
In South Korea, the regular gas has octane 91. Premium gas has the octane value of about 100.

There are a lot of reports on the 'Korea MINI club web site';
Many MINIs have experience in abrupt stoping of engine recently. People guess that it can come from the regular gas.

Finally, I think that we should depend on only Premium irrespective the octane number.

 

Octane is very important and it's key to getting the prescribed performance from your Mini. Premium is a very generic term and another man's Premium may be the other guy's Regular. Keeping the Octane level at the correct number for maximum performance is the point.

 

Yes, I agree with you. Keeping the Octane level at the correct number of maximum performance is the point.

I think that the octane level is not standardized globally yet. We should be able to depend on the octand level number irrespective a generic name.

Global gas for Global MINI..

 

There are also different octane scales that are configured differently. One is referred to as RON and the other is MON, and then there's PON (no kidding). Here's a clip that explains it (from Wikipedia):

"The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

"There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

"In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2.

"Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-95 (regular) in Europe."

 

Very good, (R+M)/2 is typical in North America. When I'm in Australia, we use and average of -6 to get the equivalent number. Good research!

 

Here is a thread on another forum about high ethanol content in Shell v-Power gas.

http://forums.vwvortex.com/zerothread?id=2855049

This is purely a FYI post. I am not editorializing. I do not know what Shell's ethanol content currently is at. But if you are running Shell gas and experience problems with the engine, it could very well be due to the quality of the Shell gas.

 

Where I live the most important criteria for selecting gasoline is how long it has been in the ground. Some stations around here sell very little premium hence the premium gasoline they do sell has a much greater liklihood of having broken down from age. My point being that there isn't much to be gained from 94 octane gasoline if it has turned into laquer prior to being purchased. That being the case, the most reliable premium gasoline around KC tends to be BP (formerly Amoco) 91.

 

The mini is a great car; but it is no Ferrari. Anything over 91 is superfluous in my opinion. 93 and up certainly isn't going to hurt, but for most people it would be a waste.

 

efficiency, mpg, and smoother power is a waste. hm. interesting.

 

and you will see that 91 gets significant timing retard at WOT. I think that before you post like this, do either some data logging, or examine the body of evidence that's already been posted. As far as it being a waste, that's subjective, and really there's no right or wrong about it. I haven't logged the data to prove it, but I think that the loss of milage with lower grade gasses is more significant than the price difference.

The power difference is larger than many of the $100+ mods people make to their cars!

Matt

 

My opinion, as stated earlier, is that for most people anything over 91 is superfluous. I never used anything over 91 in my other cars and have never experianced any side-effects. I'm not saying that you won't get more bang for your buck if you use 93+, but the facts are, most people don't require that extra umph. Perhaps we can agree on that?
If you really want that extra power, like I'm sure most of us do, by all means use >91. But 91 will suffice, and certainly will not damage your car.

 

did your other cars have 10.6 : 1 compression??

 

when I only speak for myself. Then I don't have to defend the notion that lots of people who bought the car for performance don't care that crappy gas and the power it robs aren't real issues for driving enthusiasts!

Matt

 

Pwnd!

Drobnxs Ftw!