I've noticed that the octane rating of premium-grade fuel (at least here in Indianapolis) has changed in the last couple of months. Most stations offered 93 octane, and Shell (for an additional 2¢...) had 94. Now, most stations are selling 92 and Shell has 93 (and still charging an add'l 2¢). When I drove to North Carolina this fall, I noticed that the octane rating of premium changed along the way, varying between 92 and 94 (and possibly even 91).

I see that the MTH-USA site requests the octane you'll be using, but what if I don't want to be octane-specific?

 

hope this isn't a trend to happen in other states.. My understading is that California has already moved permanently into using bad (lower octane?)gas only...

Massachusetts used to have 94 at sunoco, now only has 93 octane there.. the other stations generally carry 87 89 91 93, no 92 yet....

 

I've heard that this is a seasonal thing, so I expect Shell to have 94 again in the spring or summer. I don't really care, frankly; lower octane actually has more "energy". I am just concerned about hard-coding the ECU to use a specific octane rating and then not being able to find that level, especially when on road trips.

 

Your MINI is already "hard-coded" for 93 Octane. (that's why 93 is highly recommended in the manual.) I ran a tank of regular (87 octane) through my MINI and my gas mileage dropped by just shy of 6 MPG! Couldn't believe the numbers so I tried it again. Same results. MINI's will run on whatever octane you put in them, just not as well. The ECU retards the timing when it senses knock from lower octane fuels which effects performance quite a bit. If you have cold start stalling or "the yo-yo" effect, it gets worse as octane decreases.

$.02

 

All you can get in California is 91 octane - it's been that way since I can remember (15+ years?). I believe it's because of California's sulfur requirements. No one makes 93 octane with low enough sulfur content, so California uses 91 octane that meets the sulfur requirements. When the nation goes to low-sulfur fuels in 2007, we might see California's stations carrying 93 or 94.

 

Just curious where it says that - I just checked the 05 MCS manual and this is all I could find about octane:

"Required fuel
Premium Unleaded Gasoline,
Minimum Octane Rating: 91.
Minimum Octane Rating corresponds to
the Anti Knock Index (AKI) and is deter-
mined according to the so-called (R+M)/2
method."

page 96

 

Yeah, its been that way as long as I can remember too. Interesting about sulfer, I didn't know that, just knew it was air quality related.

 

Heh. When in doubt, read the manual, right? :-)

So, I guess this forces me to refine my original question: what does MTH do with the octane rating I specify? I'd rather stay with "91+", rather than 93 (the default on the MTH-USA web form), but I'm wondering if somehow the flexibility of the ECU is taken away by the MTH software.

 

i dont think so.. i have my file set to 91 octane.. i've ran 96 unleaded in my car before and ran just fine. i wouldnt try to run 87 with my current list of mods... (actually it makes sense that the mth file is a little inflexable to different/lower octane sence it is designed to get as much power from prescibed octane rating..)

 

The reason that we want to know what Octane you'll be running is due to the fact that we need to know the minimum octane, since lower octane will ping sooner than higher octane. The anti-knock sensor will pick it up, retard timing, and make you lose power and fuel economy. Because lower octane has higher entropy, it detonates easier, and exploding at the wrong time leads to serious engine problems.

 

Entropy is a measure of disorder. Lower entropy would me more order. I dont' think that's what you mean to say. Lower octain burns faster.

Also the post above about lower octain having more energy doesn't make sense either. The slower burn alows for higher compression without detonation.

But the part about having the tune match the octante to keep off the knock sensor is right on the money!

Matt

 

[FONT=Arial][FONT=Times New Roman][SIZE=3] Hello,
Just wanted to introduce my self here,
should have my mcs by the end of the month

From what I had learned years ago
Octane was a measurement of how fuel would combust under pressure,
(I just did a quick google and I guess I didn't forget everything !
http://auto.howstuffworks.com/question90.htm)

basic physics teaches us that when things are put under pressure,
there temp rises.

the lower the octane fuel needs less pressure to reach its burning point,

Diesel, low octane, engine with high compression, no need for plug,
the pressure does it.

Modern gas engine, too low octane gas start to flash before plug fires,
piston still on the way up, now being told to stop and go the other way !
(I hope I don't have to tell you that that's No darn good )

High Octane, does not flash on its own, needs spark to get it going.

Low Octane vs. high, low octane does have more power ounce for ounce
then high octane, but high octane can be controlled more, so with high compression engines, and modern spark control can produce more power at the crankshaft.

Well hope my first post here is well received ![/SIZE][/FONT][/FONT]
[FONT=Arial][FONT=Times New Roman][SIZE=3]
HoopsCoop[/SIZE][/FONT]

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