I've just come back from the States where there were 3 grades of fuel on sale, the worst being 87 RON and the best 91 RON.

Are they on a different system or do their cars actually run on such cr4p?

What do you do if you have a scooby?

 

I suppose subarus over there are capable of running on the low grade of petrol. After all they have a 2.5 impreza out there to get around this I assume?

 

They are not directly comparable, because of the different ways of testing, but basically US 87 is higher than Europe 87 but I regret I cannot be more specific (it may be the average of RON and MON but I someone will know). DL

 

There is no comparision between the US and European figures, i think that they call it the ROD figure instead of RON? either way, the 91 stuff is the equiv of optimax or SUL here....87 is regular unleaded.

I raised this question the last time i went to the states and was seeing all number of high performance jap cars seemingly running on low grade fuel....its simply not the case.

So ignore the values!!!!

Neil.

 

However, from experience - looking at British cars exported to the US....

USA export version always had engines with lower compression ratios (purely to avoid detonation from low octane fuel)

Examples are Jaguars from XJ6's to XJS's and Range Rovers. Obviously I may be harking back to the late 80's here, so perhaps their fuel has improved since then.

 

Although it looks normal on the pump it may perform badly. However on another day the same company may make its fuel out of a different blend to get the same RON but a different MON. This is done for profit reasons and is why you occasionally get bad fuel even though it is legally rated the same. In the past with high leaded fuels nobody noticed but nowadays high performance cars do notice (The Molemobile has just had a particularly bad batch from Total, and has been pinking all week)

In America the service stations use the Pump Octane Number or PON rather than RON. this is the average of RON and MON and gives a much better grade, and is also why the American gas always seems not as good as our when in fact it is is the same (and has better quality control). But even this system can be abused by adding octane boosters to poor fuel.


Below is an approximate comparison chart, these numbers can vary by as much as 2 grades

RON MON PON
90 83 86.6
92 85 88.5
95 87 91
96 88 92
98 90 94
100 91.5 95.8
105 95 100
110 99 104.5

 

The yanks do indeed use the formula of RON+MON divided by 2 to get the average of both, that's what they print at the pump.
We have RON at our pumps, but MON is a better indication of knock resistance at high engine speed.

Dipster