Octane rating US vs UK?????

[wilf leek]

I picked up on a totally un-related thread a while ago that there is a difference between US and UK gas octane ratings.

I believe that here in the UK, we use the RON octane rating (research octane rating?)

How does that relate to the US system, and how would one convert from one to another.

I ask because I am considering a mid-winter head skim/CR increase, and want to check out all the details before I do that. Currently running 9.5 : 1 with ally heads on a 408W.

UK fuel runs between 95 to 98 RON.

[Chaplin]

Where's Gordon Claunch?

[Mr.Fixit]

Here in the US, we list the average between the" Research octane" and the "Mechanical (or motor) octane"

(R+M)/2

If i recall correctly, research octane is usually a higher number than the Mechanical octane.

[RedBarchetta]

I stole this from somewhere on the Net....

"There are two types of octane numbers for gasoline, the Motor Octane Number (MON) and the Research Octane Number (RON). The ASTM methods for MON and RON use the same test engine, but operate under different conditions. MON is a measure of performance of the fuel at high speeds or under heavy loads, while RON repersents the performance during low speed conditions. The octane number displayed at the pump in America is the average of these two values ([R+M]/2).

All reputable fuel manufacturers determine the octane rating of their gasoline in the research lab using a special, dedicated single cylinder engine. Comparing the gasoline to a series of standard reference fuels in the test engine results in either a research octane number (RON) or a motor octane number (MON) depending on a set of operating conditions. The RON is determined with the test engine operating at 600 rpm, at standard barometric pressure, and the intake air temperature set at 125 degrees Fahrenheit. RON is primarily used to address part-throttle knock and ping problems. The MON addresses wide open throttle operation and is determined with the test engine spinning at 900 rpm, also at standard barometric pressure, and the intake air temperature pumped up to 300 degrees.

The best predictor of a fuel's performance in a street/strip machine is the Anti-Knock index (AKI). This is simply the average of the RON and MON numbers, or (RON + MON) / 2. "

Well?!?!?

Our gas in California is so bad (RM/2 method 91 octane) that I take no chances, even with a 9.5:1 stroker. I mix 110 octane (RM/2) Sunoco race gas (US $5/gal) with the 91. Mixing 3 gallons of the good stuff with 14 of the crap yields a 94.4 octane, which is plenty for this particular motor. Heck, even with 11:1 compression I could still run a little advance at the crank and not experience detonation with a 95+ octane mix. I used to drive daily a 11:1 motor on 92 octane and had to retard the timing and use an Edlebrock water injection unit when running pump gas.

FWIW, a 4 gallon (17 gallon tank) mix yields 95.5 and 5 gallons will yield 96.6 octane. I think using the racing fuel is a better choice versus the over-the-counter "miracle in the bottle" octane boosters. Most of those have alcohol in them, which would be corrosive. They also don't have sufficient additives for upper cylinder lubrication (the race gas does).

-Deano

[wilf leek]

Ok, following you so far, but here's my question:

Is there a definite and static difference between RON and MON?

In other words, how can I convert from UK RON to US R+M/2?

[RedBarchetta]

Too much to post here, but check out this link....
http://www.refiningonline.com/Engelh...ep/TCR4_29.htm

Here's a calculator, but you'll have to "guessimate" the MON value...
http://www.csgnetwork.com/octaneratecalc.html

It's not simple because the RON/MON relationship is not linear and depends on the chemical. This is the best I can do on short notice.

[scottj]

Originally posted by wilf leek


Ok, following you so far, but here's my question:

Is there a definite and static difference between RON and MON?

In other words, how can I convert from UK RON to US R+M/2?

You can't if all you know about the fuel is the RON. There is not a "definite" difference between MON and RON. Therefore you can't convert RON to [R+M/2] without knowing MON.

Examples:

For Sunoco Regular, RON = 115, MON = 105, for a 10 point difference.

For Sunoco Supreme, RON = 114, MON =110 for a 4 point difference.

For Sunoco GT100 Unleaded, RON= 105, MON=95, for a 10 point difference.
Scott

[RACER X #99]

Wilf, this may help.

http://www.smithtex.com/racing/fuelcomp.html


Cranky

[wilf leek]

Thanks for the info guys.