Chris,

Griff makes a very good point. Currently in Europe and Australia, the octane number listed at the pump is the Research Octane Number, or (RON). In the US and Canada there is a second octane number, Motor Octane Number, or (MON) that is factored into the octane rating. RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of iso-octane and n-heptane. The differences between the RON and MON are a topic for another thread.

In the US and Canada the octane number listed at the pump is the average of the two ratings (RON+MON)/2, known as the Anti-Knock Index (AKI), Road Octane Number (RON), Pump Octane Number (PON), or (R+M)/2.

Because of variable difference in the (MON) number ~ (-8 to-13 points) this means that the octane of United States fuel will rate about 4 to 6.5 points lower than the same fuel in Europe and Australia. Currently 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-93.5 in Europe.

For example Shell V-Power 99 Octane in Europe (2006 spec) has a (RON) octane of 99 and a (MON) octane of 86. That equates to a US spec of 92.5 octane (R+M)/2.

As a rule of thumb you can use the following formula to get within a 1-2 point window. To be exact you need the product information sheet on the fuel you are currently using and average the (RON+MON)/2.

RON (Euro/Australian) Octane Rating x 0.95 = AKI Octane Rating

91 RON Octane x.0.95 = 86.45 AKI Octane (US measure)
95 RON Octane x 0.95 = 90.25 AKI Octane (US measure)
98 RON Octane x 0.95 = 93.10 AKI Octane (US measure)
100 RON Octane x 0.95 = 95.0 AKI Octane (US measure)

Hope this helps.

Bob

Running a magnum motor with too high octane can cost you performance. The ecu keeps adjusting the timing until the sensor hears knock. If the fuel is so "good" the knock sensor never senses a knock it will go into a very conservative low performance timing base mode as if something were wrong. Go with the 91 which is about equal to US 87.

He doesn't have an ECU. He has carbed engines.

YEP,,thats him.

:ernaehrung004:

Looks like u know what your talking about !!!!

But i am confuised now myself,,,,,,, i need 110 octane here in US,turned timing back in germany only by 2*,,and ran german(europian) 98 and turned out to be the same or very close. Never had a problem.
So should your list be vise/versa or was i lucky over 5 years running hard???????????:cool:

Something just doesen't match !:party-smiley-004:

In Denmark we have 92, 95, 98 and 99 RON octane available. Shell is the only company to mnarket 99 RON octane.

One of the oil companies (Kuwait Petroleum) publish the MON ratings too so we can calculate the PON numbers.

92 RON octane is 83 MON which corresponds to 87.5 PON as measured in the US.
95 RON octane is 85 MON which corresponds to 90 PON as measured in the US.
98 RON octane is 87.5 MON which corresponds to 92.75 PON as measured in the US.

thanks everybody

Your stock 454mags were designed to run 87 Octane(US rating). I would bump the timing up 2* and use your 95 octane if they are the same price.

:readinghelp:ok, this is fine.

...but can you explain what you are talking about, sorry my english.
:readinghelp:
"bump the timing up 2*"

:party-smiley-004: