North America Vs UK fuel octane rating.

[QBhoy]

Guys
I am aware that the octane rating of fuel in the US is lower than here in the UK, but can someone please clarify by how much ?
I was just on YouTube and came across a video testing the difference between standard and high octane fuel. According to this video, standard US fuel is 87 ron and super/premium is 91 ron. Is this correct ?
The standard unleaded fuel here is 88-90+ron and super/premium is usually between 95 and 99

 

[JASinIL2006]

87 and 91 are the usual octane numbers for regular and premium, but you often will see 89 as a third choice, in the US Midwest, anyway.

 

[Scott Danforth]

US uses R+M /2

 

[ondarvr]

The numbers are different because of how they measure and list the octane rating, our numbers are lower because it's the average of the MON and RON ratings, and only the RON number is used in the UK. MON numbers are lower than RON, so when averaged our numbers are lower, it doesn't mean the actual performance is different though.

 

[QBhoy]

Ah. Thanks guys.
Do you not think higher octane or ron would make a difference to performance ? Surely it does ?

 

[ondarvr]

The scale used to measure the octane is different, not the product.

​Also, higher octane fuel has the potential for better performance only if the motor using it is designed to take advantage of it, so to a point this could work, but it's limited.

​Higher octane fuel does not contain more energy, so it alone won't create more power or efficiency.

 

[Scott Danforth]

To expand on above, higher octane fuel has less BTU's available. Anything higher than the motor is designed for is simply a waste

The higher the octane, the harder it is to ignite the fuel. So high compression engines with lots of spark advance need high octane fuel to prevent pre-ignition (detonation)

 

[rallyart]

Simply put, you need a high enough octane rating. If it is too low the engine gets preignition or knocking, and can be damaged, but certainly loses power.
With a higher octane rating than necessary the fuel burns too slow which does no harm, but which loses a bit of power because it burns late.
If your engine is tuned correctly you are best to use the design fuel octane rating, in any gasoline engine.

 

[Texasmark]

This is interesting. I remember before we started using the average of (R +M)/2, the pump posted octane was higher. I remember being told that lower octane fuels do better in 2 strokers (2 cycle) due to the requirement that the consumption of energy had to take place in the combustion chamber before the exhaust port was exposed.....roughly half way down the cylinder wall. In short, as "rallyart" mentioned the fuel burns fast for a "pop" rather than evenly through the compression stroke.

Around here 87 is running $2 to $2.10 currently. 89 the mid range, no price check, and 93 was $2.69 as of yesterday. I decided to try some 93 in all my engines and see how it does. So far the conclusions are:

2 and 4 strokers in lawn mowers and chain saw, weed eater, seem to start easier and run smoother. 2011 Flex fuel Silverado gets a few more mpg but not much. No real advantage here. Nothing here really to support the huge price difference, plus one has to ask the question, how fresh is the premium in the dealer's tanks since on most pumps, the 87 selector is worn out and the 93 is nice and shiny?

One of my questions is additives for engine hygiene and long term fuel storage improvements for the extra cost. Anybody have any concrete, supported data to help with that curiousity? I have seen Shell for one, advertise their hot dog fuel does this and that but no mention of what their low grade does in comparison. The question is based on how much "snake oil" to buy to keep your fuel systems working.

Every time I see a marine and row after row of boats moored there, fuel issues come to mind. How do all these boats perform when they seldom get used and fuel sits in the tanks for months and years?

 

[rallyart]

Here is a pdf from BP fuels in Australia that talks about aging.
http://www.bp.com/content/dam/bp-cou...icle-tanks.pdf
Basically, an antioxidant in a fuel additive is what lets you store it for longer. (Not the same as antioxidants in our food, however)

 

[JASinIL2006]

This is interesting. I remember before we started using the average of (R +M)/2, the pump posted octane was higher. I remember being told that lower octane fuels do better in 2 strokers (2 cycle) due to the requirement that the consumption of energy had to take place in the combustion chamber before the exhaust port was exposed.....roughly half way down the cylinder wall. In short, as "rallyart" mentioned the fuel burns fast for a "pop" rather than evenly through the compression stroke.

Around here 87 is running $2 to $2.10 currently. 89 the mid range, no price check, and 93 was $2.69 as of yesterday. I decided to try some 93 in all my engines and see how it does. So far the conclusions are:

2 and 4 strokers in lawn mowers and chain saw, weed eater, seem to start easier and run smoother. 2011 Flex fuel Silverado gets a few more mpg but not much. No real advantage here. Nothing here really to support the huge price difference, plus one has to ask the question, how fresh is the premium in the dealer's tanks since on most pumps, the 87 selector is worn out and the 93 is nice and shiny?

One of my questions is additives for engine hygiene and long term fuel storage improvements for the extra cost. Anybody have any concrete, supported data to help with that curiousity? I have seen Shell for one, advertise their hot dog fuel does this and that but no mention of what their low grade does in comparison. The question is based on how much "snake oil" to buy to keep your fuel systems working.

Every time I see a marine and row after row of boats moored there, fuel issues come to mind. How do all these boats perform when they seldom get used and fuel sits in the tanks for months and years?

I don't have the link, but recently I saw a report (from Consumer Reports, I think) that showed long term data from running 'top shelf' gasolines vs. generic. The igher quality gas with additives and detergents left behind significantly less gunk in valves, etc., than the cheap gas. They had pictures of valves after running the different gasolines and those run with gas with additives looked almost new while the others had lots of gunky build up.

 

[bruceb58]

Ah. Thanks guys.
Do you not think higher octane or ron would make a difference to performance ? Surely it does ?

It's like comparing Celsius and Farenheit. 2 different numbers....exact same temperatures but measured with a different standard.

 

[Texasmark]

Thanks for the replies. Like BP mentioned it's "Ultimate" fuel, their premium I'd suppose, one would assume more of the qualities needed by the engine, but the difference in price seems to me like "all the traffic will bear", make their profit on the higher octane, like trucks and SUVs are auto mfgrs. mainstay profit wise, and here in TX. in high demand.

Their comments helps to explain the ease in starting with higher octane fuel. Adding just before using, from sealed tanks, is worth noting. I keep fuel in sealed containers and usually topped off before using but didn't realize that besides not running out of fuel for the intended job, it improved functionality too.

 

[QBhoy]

It's like comparing Celsius and Farenheit. 2 different numbers....exact same temperatures but measured with a different standard.

that's why I said "octane or ron" Bruce

 

[bruceb58]

that's why I said "octane or ron" Bruce

ron is a measure of octane. That would be like saying "temperature or Celsius".

Post #4 said it perfectly!

BTW, higher octane doesn't mean higher performance in an engine that doesn't adjust timing based on knock. If your engine doesn't knock on the lower octane fuel, higher octane fuel is a huge waste of money.

 

[H20Rat]

If you want serious octane in the US, run e85 or a mix... Depending on the blend, E85 is 110+ octane, and with the correct engine tuning, you can make a lot of power on it, even though the BTU's are substantially less. And as others have mentioned, running higher octane premium in an engine that doesn't require it is actually giving you less power, not more. Especially in smaller 'dumb' engines like an outboard or lawn equipment.

 

[Scott Danforth]

If you want serious octane in the US, run e85 or a mix... Depending on the blend, E85 is 110+ octane, and with the correct engine tuning, you can make a lot of power on it, even though the BTU's are substantially less. And as others have mentioned, running higher octane premium in an engine that doesn't require it is actually giving you less power, not more. Especially in smaller 'dumb' engines like an outboard or lawn equipment.

or buy 106NL aviation fuel or buy 110 race fuel. (the av gas is cheaper than the race gas) however unless your running 14:1 compression on a big-block drag car, its not needed.