Hi all,

I was wondering! I've been putting 91 octane in my MCS, as per the recommendations in the MINI book but someone told me that "burns too hot, and doesn't need that high an octane, anyway."
What do you guys think?

Wench

 

I'd follow the factory recommendation.

As the MCS is supercharged, it does not behave like a normally-aspirated engine. The idea that premium gas "burns too hot" does not bode well for your friend's credibilty on this issue.

What is the MCS compression? Isn't it still 8.3:1? I assume this figure is low due to the supercharger. Can someone please explain what the effective compression ratio would be on full boost?

 

Wench,

I'd definitely follow the MINI Owners Manual recommendation, which is that we only use Premium fuel, a minimum of 91 octane.

When I drive Wanda cross-country and back, if I have 94 octane fuel available, I will alternate, at half-tank only, with medium grade IF it is 90 octane, which some of it actually is.

Hope this helps.


Clover

 

I did some poking around, as I'm also curious about this question. I found this quote from MartyR -- sounds reasonable.

"MCS static CR is much lower because of the increase in effective CR when under boost generated by the supercharger. Effective CR under full boost (stock) with the MCS is well upwards of the 10.6:1 CR of the MC (probably approaching 13:1 or more). Pulley-equipped cars running higher boost levels are seeing even higher effective CRs. And the S motor is built accordingly."

Hope this helps... :smile:

 

thanks, all of you! I really appreciate all the feedback, having driven a truck for so long, I just wasn't sure... Hey Clover, where do you find 94 octane, I feel kinda stupid- I've never even seen it!

 

I'm a by the book person, so I've only bought one tank of gas, but I used 93 Octane.

 

I don't think that you can get it any where near you. Of course, the Sunoco down the street from me has 93 and 94 octane

 

I think that it was either in Louisiana, Texas or Mississippi! It was somewhere in the South....not in Cali!

I take a big roadtrip every Spring to visit my MINI friends before heading up to the MINIs On The Dragon Meet the first full weekend in May, every year.


Clover

 

Octane question update:

I'm still trying to reconcile the Antiknock Index (pump octane rating) to the RON/MON numbers.

MINI has designed the MCS engine to operate on 98 RON octane. Unfortunately, U.S. "pump octane" (the Antiknock Index) is determined by the "RON+MON/2= pump octane" formula. The result of this is not knowing if you're buying more or less than you need, based on the orignal Euro design specs.

I know this is geeking-out a bit, but it's fun to learn new things... anybody have a source that lists the RON/MON octane ratings of U.S. gas?

 

i dont know, that 109 i put in the tank that one day made it run fast....lol

too bad its 4 dollars a gallon, or i would use it more often

 

At a Mini-Picnic in north Jersey last weekend, someone with an 05MCS told me since we can't get 91 octane in NJ or PA, he puts in a half tank of 89 and a half of 93...says that might = 91.

Anyone ???

hs

 

Well, I think that the Owners Manual means that we need to use a minimum of 91 octane, not that it is the only correct octane. I mix 94 and 90, 50/50, when possible on my roadtrips across the US, but only to save $$$. Hope that helps. :smile:


Clover

 

When down here you need to get off the beaten path to fill up. Then you can get some good go juice for Wanda. 190 proof.

 

Hey, SB! I'm still looking for a good moonshine connection when I'm in your neck of the woods! You'll have to PM me with the pertinent info!


Clover

 

Will do.

 

I found one of those "everything you ever wanted to know about" sites on the net (this one deals with gasoline, of course). According to the site, octane ratings do indeed follow mixing ratios. With this in mind, 93+89 octane will equal 91.

You've been warned -- it's pretty dry reading...

Gasoline Geek site

 

http://townhall-talk.edmunds.com/WebX?13@@.eea6c81/2062

Check out my question #2063 and the answer from somebody from Canada and his experiences with the various octanes.

hs

 

Sunoco uses the blending technique at the pump to get their various grades out of two ground tanks. I have been running 93 (BP) on most fillups and this last time put in 89 (Mid-Grade) into a half tank of 93. I'm not running a pully on my 2005 MCS and didn't notice much difference... may a bit quicker... but it was cooler outside also. I suspect it would take some instrumentation (dyno) and controlled experiments to really get some definitive answers.

My opinion after reading about this quite a bit, on this forum and other car forums, is that beyond a certain point, more octane does you no good... and taken much above the required amount, it hurts performance. The flame front is slower, given the same compression and conditions, on higher octane fuel.

 

Thanks, Solarmax. I didn't know Sunoco blended on site. But wouldn't you want to try more than just one tank of hybrid before drawing conclusions?
I'm going to try it for two or three tankfuls and report back.

Whoops, just did some 'rizmatic. Say I drive 20,000 miles @ 29mpg; what I'm now getting. Here in NJ, 93 is $2.20. That rounds off to about 700 gallons. Cost: $1540.

Octane 89 is $2.10. So 350 gallons = $735. 350 gallons of 93 = $770.

Total: $1505. vs $1540 = $35 per year.

At the risk of sounding like a spoiled rich kid, it's interesting but not worth the effort.

hs

 

Remember, to take advantage of higher octane fuels, which by nature have higher burn points (or is it called flash or something else ), you have to change the ECU programming (maybe plugs too ). Otherwise the stock programming cannot adjust timing, etc. far enough, resulting in not all of the fuel combusting...which means less power. MINI specs out the range of octane the stock programming is good for. It something like from 91 to 97 or so for the MCS.