Pump Gas Octane No.s USA=UK?

Just wondered if US octane numbers use the same system as UK? Pump gas (petrol as far as I'm concerned ) seems to be around 91 octane in US IIRC, whereas standard in UK is 95, with super being up to 99 depending on brand (total 97, BP 98, shell 99, tesco 99).

Assuming the numbering system is the same, and timing is altered to take full advantage, then US figures (providing supplier ishonest) should be a conservative estimate of power when used in UK even on std petrol?

Are there any issues (can't think of any) using higher octane fuel e.g. 99 rather than 91?
Thanks
Jono

No they are not the same. I think this has been discussed before but here is an entry from Wiki:

"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 IndexAKI), 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 USCanada, would be 91-92 in Europe. ( and

Basically, the "premium" fuel available at stations in both locations are the same (excepting special cases, race fuel, etc.). Our 93 octane rating (what you get in the US differs, where I live on the East Coast 93 is common, not so in California and other places) we get here is equal to your 98 or 99.

If you are still not convinced have a look at what manufacturer's recommend for minimum fuel ratings for their engines - some of which are identical from country to country. Or, ask yourself what would you run a 10.5:1 compression engine on? I'd say 93 octane pump gas, you'd probably say 98 or so. Same engine, same compression, same gas but different labeling (yes, there are regional additives etc. that complicate this matter, especially in CA or "summer blends" in the US, but I'm just making a general explanation).

Ron

would agree with the above except manufacturers often spec their engines differently in the USA to other places. For example the WRX I had whilst living in the states had 1psi less max boost than the euro version of the same car and it was specified to run 93 octane.

My assumption would be either the manufactures have quality or availability concerns on the getting the "good stuff" in the USA. I suspect the state to state variance in blends leads to manufactures working with the lowest common denominator.

Ahh, had a feeling that may be the case.
Cheers guys

Doug68 said:

My assumption would be either the manufactures have quality or availability concerns on the getting the "good stuff" in the USA. I suspect the state to state variance in blends leads to manufactures working with the lowest common denominator.

Click to expand...

This is true. Gasoline variations across the US can be large, in the summertime especially. CA mandated a number of specific clauses with additives that have to do with emissions. In fact, for a long time in the 80s and early 90s there were CA emissions spec cars, and 49 state cars. Sometimes there was no difference in performance with a car, sometimes there was. As of now just about all cars are 50 state cars, which means they meet CA's CARB emission requirements.

Where I live 93 octane is always present, but in some areas of the country this is replaced by 92 or even 91 octane. Heck, I was up in NJ recently and those poor folks can't even pump their own gas from what I can tell, an attendant must do it for them by law. Talk about propping up the work force....

Ron

Ron Earp said:

Heck, I was up in NJ recently and those poor folks can't even pump their own gas from what I can tell, an attendant must do it for them by law. Talk about propping up the work force....

Ron

Click to expand...

Yep - NJ law. Always throws me for a loop when I visit

Ian