Octane GAS RON or MON?
 

Hi guys! I am a bit confused. What is the best fuel to use with our Fds? On which reading should i follow RON or MON ? RON reads much higher than MON. Should i follow the MON readings to play safe?

Running low octane, would result in bad idle too?

Thanks in advance!!

You want 95 RON or better.

For those of us with lesser IQ's, what is RON and MON and where are you getting those readings?

Mon ratings is fuel tested under greater load, harsher conditions and higher rpm etc. The higher the mon rating the more resistant the fuel to detonation or self combustion.
Ron rating is tested under light load. less harsh conditions and less rpm thats why for a given fuel ron rating is always higher than mon. When looking for the best fuel with regards to it's ability to withstand self comsbustion or detonation you always go for the fuel with the highest mon rating. That why fuel like c16 works better than say sunoco 120+ ron because the mon rating is higher, even though the ron rating is lower.

rgds

Brian

Brian, all the reading I've done explains that RON, MON, and PON (which is the average of RON and MON) are direct conversions.

Do these conversions only hold true for passenger-car fuels? Your example uses race fuels, which of course is a bit beyond the scope of the original question.

Dave

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

The octane rating may also be a "trade name", with the actual figure being higher than the nominal rating.[citation needed]

It is possible for a fuel to have a RON greater than 100, because isooctane is not the most knock-resistant substance available. Racing fuels, straight ethanol, AvGas and liquified petroleum gas (LPG) typically have octane ratings of 110 or significantly higher - ethanol's RON is 129 (MON 102, AKI 116). Typical "octane booster" additives include tetra-ethyl lead and toluene. Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition. This is why leaded gasoline has a higher octane rating than unleaded.

Brian

Thanks Brian!! Great info!!

Should the case be that i am running low octane, would this effect the idle ?

Thanks

If your gas has a MON rating, you will want it to be at least 91. Do NOT run lower octane fuel, especially if you are modified. And octane level isn't going to effect your idle at all.

Thanks rynberg! My problem all started after fitting a Knightsports ECU. The idle is all the time bouncing and very low. I also contacted Knightsports and they told me that the ecu is setup to work without the airpump. So i disconnected the airpump but to no improvement. So i was thinking it was a problem related to fuel. Knowing that in Japan they use 100octane fuel.

Now i refitted the original ECU and all is back to normal. However, i'm still tempted to refit the Knightsports ECU and try solve the problem.

Take my advise the knightsports ecu's are crap chipped ecu. They come pre mapped for specific mods. If you don't know what mods or fuel it's ben mapped for
plug it out, imo even if they did tell you what fuel and mods it had been mapped for i'd still rip it out. get yourself a standalone and have someone set it up properly, otherwise I would stick with the stock ecu.


Brian

THanks BNA ELLIS ! I guess its better to listen to your suggestion. I'll try to get my hands on an APEXi ECU...

Thanks to all !!