Why is this? I'm confused
 

Hi
Since I bought my mini cooper s 2007 I was always advised to use high octane super fuel in it.

The car never felt right, the engine sounded awful and oil consumption was on another planet...Start motor sounded clunky when cold..

I have been to the garage and they checked the car over, said there was no leaks or anything..

So... I read somewhere on a forum that I should try using normal unleaded..

I was sceptical.. but I thought okay why not..
So I filled up with standard unleaded.

Car now sounds right... starts in the morning without the clunk splutter...drives like it should have driven...oil consumption not nearly as bad.

I'm confused... I thought the more expensive fuel the better... I don't know what to say only that I've been proved wrong.

The only thing I have noticed is now the car appears to be missing the loud popping from the exhaust which I quite liked..

Has anybody else ever noticed this?

I've been wondering about this a well. The owner manual says 89 minimum, 91 is recommended. I have a 2012 MCS, just recently tried 89 (didn't seem to cause a problem). I haven't heard the noises you have, but I don't think I'd go all the way down to 87, Mini must have a reason. Am sure lots of others will chime in..

The S model needs high oct. I think non S is a 10.6:1 compression ratio motor. Most high output motors to displacement from Europe require higher oct because of the higher compression. Europe has better fuel than we have in the US so our lower oct fuel is even lower than the motors are designed for. The computer is adjusted on US spec cars and the computer will adjust the spark and air mixture to allow the motor to run on lower 87 oct but it is not running at its optimum spec. The higher efficiency or higher MPG is created because higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. I am not sure what the ramifications are if the lower oct fuel is used on a Justa because the knock sensor will "help" prevent damage from detonation. Pre-Ignition due to improper oct can melt spark plug electrodes. I would not risk it. Lower compression motors like 8.5:1 run better on 87 oct and higher oct is for 10:1 and up.

100% I can say that the car completely changed after filling up with regular unleaded.. It feels like the car should have felt since I bought it 2 years ago.

I'm baffled..

No, they don't have better fuel. It's basically he same, except for sulphur content. They do measure octane differently.

In the USA we use the average of the (research octane number+ motor octane )/2 method, in Europe, the use only the RON... But it's about the same gas.


As for what # to use, it depends... Altitude, load, %ethonol, water in said ethonol, temp...

But in general for a MCS or JCW, use the highest available octane, from a top tier retailer... Those of you with only 91 are already at a disadvantage...

If no other factor is responsible, the only way I can see fuel affecting the car this much is the water or ethanol content must be significantly different in that tank fillup from what you have been using. More likely there is another factor, like - did you just get an oil change recently? Maybe there was a vacuum hose loose that the guy secured for you and did not think to mention it?

I would like to understand this better.
The way I understand it, in the US 91 AKI (95 RON) is the maximum octane available except in some east coast states that offer up to 94 AKI (98 RON). Outside of Cali I have seen 93 posted on some pumps but 91 and sometimes 92 is what is posted in my state. If you want race gas you can get 100 but it is not available at most (very few) stations. In this post we are talking about "not even" using 91, we are talking less than 91.

http://upload.wikimedia.org/wikipedi...ne_Ratings.jpg

95,98 and 100-102 RON
Super Plus E5" 98 RON (ROZ) is available in Germany. Shell or Aral offer 100-102 RON gasoline (Shell V-Power, Aral Ultimate) at almost every fuel station. European stations due to the EU are required to offer a minimum rate of "Super" at 95 RON but 98 and 100 is still available.

http://i764.photobucket.com/albums/x...e/IMG_1592.jpg
http://www.emsdettenervolkszeitung.d...ion=1314712181
http://i46.tinypic.com/35k7dki.jpg
http://www.motortrader.com.my/news/w...7/DSC_0590.jpg

Most likely you need to do a carbon clean and have the timing chain tensioner checked. That is probably your problem and not what octane you are using. On all F/I cars it is advised you use higher octane because of the reductiin in detonation with car screw your engine up for good.

oh god.. Timing chain tension er... I've had 2 of those replaced already.. :(

how many miles? You can hear the chain rattle on cold starts when it starts to slacken up.
I would run some seafoam through the valves to clean carbon (how to under the modifications section) and change the spark plugs. Maybe they are corroded or the gap has widened.
Maybe a walnut shell blasting is in order. I'm researching how to do that myself now.