place up the street sells 100 octane. i wouldnt mind droppin some in but, i want to know if its a bad idea.
any thoughts?

 

won't hurt your car, but won't really help either, kind of a waste of money. . .

unless the knock sensor is causing your ECU to pull back the ignition timing, you won't notice a difference. . .

if you were to advance your ignition timing to go along with the 100 octane fillup, it might net you a couple hp though, although I don't think there is a very easy way to do this on the MCS (on the Mazda3 there is a way to spoof the crank position sensor to advance timing, I don't think a similar trick exists for the MCS though. . .)

 

no sense in using high octane unless your map has been altered.

 

I really think that this is false and all of us tell eachother the same thing: " 100 is wasted money. "

The most scientifically accurate and comprehensive article on octane and high compression engines says things a LOT different. This is really fascinating, I read the whole thing, it is kinda huge. Check this section out. It speaks of optimal situations for cars that arent computer monitored and controlled and that do not also have the ability to retard timing during knock. Now, this to me, is the explanation of optimal gas octane levels for a particular engine. If you read you will see how crappy your performance is when the computer makes up the slack for bad octane gas. It wont knock but it will be a significant hit performance wise.

Keep in mind that the lower compression number of an mcs exists compared to the 10.6 of the MC regular as we have supercharged air which makes up for that difference. In short, we need as high or possibly higher octane levels than a MC regular.

"Low compression ratio engines are less efficient because they can not deliver as much of the
ideal combustion power to the flywheel. For a typical carburetted engine,
without engine management [27,38]:-

Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

Modern engines have improved significantly on this, and the changing fuel
specifications and engine design should see more improvements, but
significant gains may have to await improved engine materials and fuels."

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

Basically, these are the optimal ratios at certain temperatures of air entering. 91 is about 10 points lower octane level than we need.

Fascinating read, everything else is a partial story.

 

note: make sure it is unleaded.

 

bingo!!


DO NOT put leaded race fuel in your car. it will tear the injectors up and also clog the converter in the exhaust.


Lead in new cars is no good

 

Well for my 2 cents, I put 100 octane when I go to the track. I reallly don't notice any significant power or performance increase. But... I have noticed that the car runs quite cooler, particularly on a hot day. I have no idea why, but it does.

 

you can gain quite a bit from octane... the reason is the car will not knock on 100...no knock means 30 degrees of timing.... on 91 the car will dioal back to as much as 18 degrees... that's almost a 20 whp drop....

 

Don't the lower octane gases contain more punch, anyhow? Octane is only about controlling for knock isn't it? More power from your gasoline comes from using the lowest octane gas you can find and still not have any knocking, I always was told. But with all these ECU units messing with your timing anyhow, I don 't really know what you should do.

 

The way I always defined Octane, is "The fuel's resistance to ignition". In other words, the higher the octane, the more pressure/spark it requires to ignite that fuel. This means you can run a higher compression ratio which allows for greater power. This is all pretty cut and dry on a naturally aspirated non-computer controlled car. Things get a little more complicated with today's computers, but really only in the sense that the computer can adjust timing and often valve duration on the fly.

In the olden days, you could run low octane fuel in a high compression V8, but to do it, you had to get out the timing light and and tools to manually retard the timing. Not much fun...

 

So aren't you saying that after you build a higher compression motor to put out more power you then use high octane fuel in it, right? If a motor is still stock the higher octane gas isn't going to do anything for it, is it?

 

Nope.

MINI = High Compression

 

As stated earlier, the higher octane will help in those circumstances where the timing is retarted. The only real way of knowing when it's being retarded is by plugging in a computer. The MINI needs high octane because of the high CR on the MC and the forced induction of the MCS. Some members on this forum have found that even on 93 octane, the MCS will retard timing in certain circumstances. 100 octane would not require retard. The thing is that while the 100 octane will not require retarded timing (that would lower hp), it is harder to ignite (thus loosing hp when the high octane is not needed)

On a carbureted car where you have a set advance curve, you won't see any performance increase unless you change the timing. The computer takes care of it on modern cars but the statement in the last paragraph still applies.

 

The computer retards the timing stealthily and INSTANTANEOUSLY on the first knock moment. then goes to a crappy efficiency. the computer doesnt allow for the same power with worse gas, it allows the engine to not get hurt by crap gas and crap octane levels.

100 is a great octane to use although it might be cost inefficient in a rather extreme way.

 

thanks for all the info. i feel like i just took a 6 month course on octane in 15 minutes!!!!

now if someone could explain how i hit the lotto i'd really appreciate it!!!

 

No, not really, on hot days, you may reduce risks of detonation but todays computers take care of that stuff.... on the flip side, I guess its possible that if you put higher octane fuel into a lower compression engine, it may have a harder time getting a consistent even burn of the intake charge - meaning, you'll get unburnt gas thought the exhaust, which may show up as black smoke. I'm not totally sure about this point though.

 

the gas never burns completely anyways.

 

But higher octane will burn less and with less ferocity than lower octane.

 

My MCS is pure stock, no ECU mods, no hot sparkplugs, etc.. stock stock stock..

I've mixed in 100 octane with our california 91 octane, ok that gets me 95 octane if it was evenly matched.. I read somewhere that the MINI was designed more for 93 octane (which we don't have in California) my classic Mini says it wants 96 octane, but this may be a different standard in europe than what we have in the states.. ..it seems to run a lot better with the 100 octane, but then its old 1275 is quite different than my new MINI's uh.. I am not sure what it is

I've also been under the assumption that using octane booster every few fill-ups was good for your car. I wait until the red light goes on before filling the tank.. next stop I pour the bottle of octane boost in, then fill up the tank.

In both cases, my OBC says I am getting better gas milage.. do I? I don't know, really, but the car seems to run better.. what I mean is, the engine seems to be needing less RPM's to get up to speed, it's working less hard to get up a hill for example.. now it may just be my imagination, but it seems to perform better, quicker.. I haven't timed it and I certainly aren't going any faster than usual, it just seems to get there with less effort. Is it all in my head and clever marketing? Or is the higher octane RACE GAS and BOOST really doing what it says it's supposed to?

 

When I lived in Italy for 3 years leaded fuel was the only thing available for my 3-series. I have never noticed any ill-effects but I'm sure over a long period of time this would be true. I was told though to at least change the fuel filter.
As for the Mini...100 octane will not hurt the car and it does produce HP gains. BUT, the computer can only compensate up to 96 octane or so before it is a waste of money (unless you have a chip for that octane rating). There is a 76 station that sells 110. I have mixed 50/50 and have noticed some power increase. But, I wouldn't do it all the time. Especially when a fillup is like $80.

 

from what i read about computers IN GENERAL not necessarily something odd with the mini, is that they compensate for improper octane levels to protect the engine. I would think that the proper octane level would do well regardles s of computer control.

 

This is correct. 100 octane makes a significant improvement in performance due to ignition advance.

 

(Fireballed) Tuls...you can not come back from the grave. You have been banished from The Church Of NAM and shall only roam the Underground!

 

Here is an excerpt from the Engineering paper published about the MCS engine by the Engineers that designed it.

"The best shape for the combustion chamber with regard to both efficiency and knock resistance was obtained with a piston containing a lenticular combustion chamber bowl measuring 1.6 cm. With the aid of knock control, this makes it possible to use 91 to 98 RON fuels throughout the world. However, the basic design has been optimised for RON 98."


Remember that in the USA we measure our octane as (MON+RON)/2.

This has been said to mean our fuel is rated 3 to 4 Octane lower than it would be rated in the E.U. So you could take the statement to mean the engine is optimized for USA 94 to 95 grade. The lowest grade around here is 87 which would seem to correlate with the 91 in the paper.

John

 

As Scavenger said, the 100 octane will help, only due to the fact that the cars ECU will not retard the timing back as much.

Modern cars constantly change timing as you drive them. The computer will actully advance timing so the car almost pings, and then retards it back, using the knock sensor to detect this. (the car does this over and over as you drive) It normally happens so fast and so slight that the driver is unaware. This helps the car run at maximum efficiency and gives the best performance.

So if you are using 91 octane, then the computer will have to retard the timing sooner to prevent ping, where as with 100 octane the car can countinue to advance the timing and produce more HP before cutting back on the timing.

Edit: Octane in the fuel is only to prevent premature combustion in the chamber do to high compression, as someone else already stated.