chris-jack

we can get only 91 and 95 octane fuel, nothing less. its the same price! in the future they are planning to sell only the 95 in austria. should i do a timing adjustment to go with 95 or is it fine like it is?

chris
454 mag

DMOORE

I have a feeling your motor won't know the difference.


Darrell.

chris-jack

wow, thats intresting. so, would you recommend me to go with 91 or 95. as i mentioned - the same price. i always thought: the more octane, the better, but lower octane also has its advantages. and maybe this summer there will be only 95 available. adjusting the ignition point could be necessary. am i wrong?

Griff

First thing is to find out how your octane measurement compares to US octane ratings.

chris-jack

ok, that fine, will call him

Hanisch GmbH
Reichelsheimer Str. 10
55268 Nieder-Olm

hope this is correct

Planetwarmer

Do you know what the compression ratio is on your engines? If it is low to medium, use the 91 octane. If you have a 12.5:1 or blowers, use the high octane.

I bet you do not have high compression with a stock 454 mag. 91 octane in the US is plenty for that motor.

chris-jack

yes, i know that 91 is enough, but i cant get that stuff!!! what happenz when i use 95? i think there is no problem wih it, but maybe i should think about adjusting something to the much higher octane than recommend.

4mulafastech

I agree, do this first.

Running higher octane than required won't hurt your engine, it just might lose a little power (very little). Higher octane fuel burns a bit slower, and with a low compression engine you might not get a full burn on the power stroke. Advancing the timing can help if you run into that situation, but personally I wouldn't mess with it.

rmbuilder

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

Pismo10

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.