s.g.erickson

The gas stations in my area never seem to have a fuel with the suggested octaine rating that is in the manual. Always a couple points lower. What effects does this have on performance and or maintenance? What is RON? Is it acceptable to use an octaine booster?

Rennen

Octane retards ingition. The higher the octane, the more the computer can advance the ignition so the fuel is burned more efficiently and you can derive more power from the stroke. Burning lower octane gas yields heat induced pre-ignition or "pinging". The computer uses knock sensors to detect this and back off the timing of the ignition so your engine is less efficient and produces less power.

Rennen

Oh, and by the way, predetonation is basically the fuel/air lighting up on the compression stroke while the piston has not yet finished compressing the mixture, so the engine ends up working against itself. It commonly feels like partial throttle.

Smokin

From Ask.com...

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Antiknock Quality of the Fuels (Octane Rating)

The octane rating defines the gasoline's anti-knock quality (resistance to pre-ignition). The higher the octane rating, the greater the resistance to engine knock. Two differing procedures are in international use for determining the octane rating; these are the Research Method and the Motor Method (DIN 51 756; ASTM D 2699 and ASTM D 2700).

RON & MON

The number determined in testing using the Research Method is the Research Octane Number, or RON. It serves as the essential index of acceleration knock.

The Motor Octane Number, or MON, is derived from testing according to the Motor Method. The MON basically provides an indication of the tendency to knock at high-speeds.

The Motor Method differs from the Research Method by using preheated mixtures, higher engine speeds and variable ignition timing, thereby placing more stringent thermal demands on the fuel under examination. MON figures are lower than those of RON.

Octane numbers up to 100 indicate the volumetric content in percent of C8H18 iso-octane (trimethyl pentane) contained in a mixture with C7H16 n-heptane at the point where the mixture's knock-resistance in a test engine is identical to that of the fuel being tested. Iso-octane, which is extremely knock-resistant, is assigned the octane number 100 (100 RON and MON), while n-heptane, with low-resistance to pre-ignition, is assigned the number 0.

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I've read that the RON method is not used in the US but I could swear I've seen it before. You probably won't see octane rating as high as what is referenced in the manual. I think it has to do with the different ways octane ratings are obtained in different countries. The "RON" method may show a higher number than the "MON" method on the same gas. I'm not sure... I'm not a chemist. I do know that if you use lower octane gas in a higher compression engine you will have a problem. Higher compression engines require higher octane fuel... Or racing fuel. That's why most cars in the US are built with 11:1 compression or under... So they will run on pump gas. When you get above that you'll need additives or racing fuel to avoid predetonation and damage to your engine.

I use octain booster in my tank at every fill-up. Works for me. I notice a slight improvement.

D_Schultz

[QUOTE=Smokin]
I've read that the RON method is not used in the US but I could swear I've seen it before. [QUOTE]

In the US, all gas stations state their octane rating as (RON + MON)/2.

So you could say the RON method is not used here (at least not directly). All pumps should have a sticker showing the formula (RON + MON)/2 & many states will also have a disclaimer that all grades may contain up to 10% ethyl alcohol.

robbed666

YEP! they call that, you've guess it ! "PON" Pump Octane Number

see link for more info MON, PON and RON

Tom W

The other factor to consider is that at 5400 feet you have less oxygen to burn too, so the lower octane isn't a big concern in Denver. Just use the pump premium grade (91 or better) and you will be fine.

Smokin

I think his point is, the higher the altitude the lesser the performance because there is less oxygen. Most manuals for all vehicles these days have special sections about high altitude driving. Some or most will tell you that performance will suffer as you go higher. They will also warn you about the potential for overheating.

Smokin

Off the top of my head I'd say the air is thinner, meaning a less dense charge of air into your cylinders. More air in (with proper carb settings) means more power. Less air means less performance. I know it can cause slight performance issues but I think you'd pass out from lack of oxygen (If you drove that high) before you'd see significant power loss.

I think Tom meant that with less air there may be less chance of predetonation since it can't flash off as easily.

Just a guess on my part...

Smokin

You know... I don't know about anyone else... But my car doesn't knock... and I've never heard it knock. I always use the highest octane I can find and then throw a can of octance booster in. Every third tank I add a can of injector cleaner.

Tom W

My comment was based on a discussion we had a year or two ago in a thread. You may be able to find it in the archives. Regardless of the altitude issue, our cars run fine on the 91 octane found in the USA. You can read more by going to the Rennsport systems web site. Steve has a lot of good informaion avaiable on his site.