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      07-14-2017, 05:50 AM   #1
Lobb
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Question US Gasoline octane ratings

A question from over the pond. In the UK our gasoline is octane rated using RON.
We have two choices, 95RON and 98RON. Typically, you'll find BMW drivers using the higher octane 98RON gas, as the knock sensors on the car allow a little more performance.

How does it work in the US? What would your equivalent to our 95 and 98 RON be?

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      07-14-2017, 06:39 AM   #2
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I know 98 over there equates to 93 in the US. I'm not sure what 95 is equivalent to here. You can only get 93 octane on the East Coast though. A general rule of thumb is once you pass the Mississippi River, the highest octane is 91.
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      07-14-2017, 06:44 AM   #3
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https://www.etuners.gr/fuel/
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      07-14-2017, 06:49 AM   #4
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Thank you, so 95 in Europe is 91 here in the states.
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      07-14-2017, 07:04 AM   #5
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UK uses RON (research octane number); US uses anti-knock index (AKI) which is the average of RON and MON (motor octane number):

RON - MON - (R+M)/2
95........87........91
96........88........92
98........90........94

Had to deal with this for three years living in Italy and now the last two years in the UK.
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      07-14-2017, 08:08 AM   #6
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Thanks guys. Much appreciated
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      07-14-2017, 02:38 PM   #7
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Yeah this causes confusion all the time. I see guys running tunes thinking they can use the race gas setting because they have "98 octane"...
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      07-17-2017, 01:32 PM   #8
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Quote:
Originally Posted by MGM135is View Post
I know 98 over there equates to 93 in the US. I'm not sure what 95 is equivalent to here. You can only get 93 octane on the East Coast though. A general rule of thumb is once you pass the Mississippi River, the highest octane is 91.
It's further west than that. It begins at the higher elevations. From what I've researched it's a standard developed and put in place for typical power generation from naturally aspirated, carb'd engines from back in the day that no longer apply...especially not to vehicles with FI. Now that does not mean you can't find higher octane fuels at higher elevations and all the way out to the west coast, but it is FAR less common. An example here in TX is traveling on I-10 West from where I live out to my former home town in West Texas, the 91 switch was in Sonora, TX. However, on my last visit home in 2011, I found 93 to be quite common in the city. Before that, I only knew of 3 stations in the area that carried 92. 93 is mostly the norm east of a line drawn through TX from Sonora. I see very few stations that carry below that level of premium gas, save for a couple 92's I've run across at random.
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      07-17-2017, 09:29 PM   #9
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Worth noting that California is 91 as a max. I'm sure it's just coincidence, but the old 135i ate three HPFP once I moved to TX and used 93. Never an issue in CA.
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      07-17-2017, 09:33 PM   #10
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93 is available at most gas stations in Oregon.
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      07-17-2017, 10:10 PM   #11
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Quote:
Originally Posted by davis449 View Post
It's further west than that. It begins at the higher elevations. From what I've researched it's a standard developed and put in place for typical power generation from naturally aspirated, carb'd engines from back in the day that no longer apply...especially not to vehicles with FI. Now that does not mean you can't find higher octane fuels at higher elevations and all the way out to the west coast, but it is FAR less common. An example here in TX is traveling on I-10 West from where I live out to my former home town in West Texas, the 91 switch was in Sonora, TX. However, on my last visit home in 2011, I found 93 to be quite common in the city. Before that, I only knew of 3 stations in the area that carried 92. 93 is mostly the norm east of a line drawn through TX from Sonora. I see very few stations that carry below that level of premium gas, save for a couple 92's I've run across at random.

Oklahoma is 91 only also.
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      07-17-2017, 10:13 PM   #12
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Quote:
Originally Posted by smrtypants44 View Post
Quote:
Originally Posted by davis449 View Post
It's further west than that. It begins at the higher elevations. From what I've researched it's a standard developed and put in place for typical power generation from naturally aspirated, carb'd engines from back in the day that no longer apply...especially not to vehicles with FI. Now that does not mean you can't find higher octane fuels at higher elevations and all the way out to the west coast, but it is FAR less common. An example here in TX is traveling on I-10 West from where I live out to my former home town in West Texas, the 91 switch was in Sonora, TX. However, on my last visit home in 2011, I found 93 to be quite common in the city. Before that, I only knew of 3 stations in the area that carried 92. 93 is mostly the norm east of a line drawn through TX from Sonora. I see very few stations that carry below that level of premium gas, save for a couple 92's I've run across at random.

Oklahoma is 91 only also.
Really? My Father in Law lives there and I'd never noticed that. Guess that gives away that I don't really pay attention when on the highway.

I'm in Dallas and we have exactly zero ethanol free options. I'd trade 93 with ethanol for 91 with none all day. Stupid f'ing subsidies.
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      07-18-2017, 01:50 PM   #13
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Quote:
Originally Posted by smrtypants44 View Post
Oklahoma is 91 only also.
I was speaking of TX, specifically. OK is still quite a bit west of the Mississippi River, but so is half of TX.
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Last edited by davis449; 07-18-2017 at 01:56 PM.
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      07-18-2017, 02:12 PM   #14
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Quote:
Originally Posted by davis449 View Post
Quote:
Originally Posted by smrtypants44 View Post
Oklahoma is 91 only also.
I was speaking of TX, specifically. OK is still quite a bit west of the Mississippi River, but so is half of TX.
Is there another half of TX I don't know about? Pretty sure it's all, or 90+% west of the Mississippi.
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      07-18-2017, 02:22 PM   #15
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Colorado (yes, it is west of the Mississippi) is unfortunately 91 max.
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      07-18-2017, 02:28 PM   #16
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As is NM.
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      07-18-2017, 03:49 PM   #17
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Quote:
Originally Posted by Red Bread View Post
Worth noting that California is 91 as a max. I'm sure it's just coincidence, but the old 135i ate three HPFP once I moved to TX and used 93. Never an issue in CA.
I can buy 103 about 3 miles from my home. I used to have to drive about 30 miles to one station to get it.

For SOME stupid reason I used to want to put it in my motorcycle. Until I had to replace jets and things. . .
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      07-19-2017, 09:40 AM   #18
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Quote:
Originally Posted by Red Bread View Post
Is there another half of TX I don't know about? Pretty sure it's all, or 90+% west of the Mississippi.
I was referring to the "half" of TX that serves primarily 91 octane as premium gas as opposed to the other half that serves primarily 93 octane as premium gas, therefore further negating the "West of the Mississippi River" generalization as well as your "Well, OK is 91" statement..
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      07-19-2017, 10:20 AM   #19
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Quote:
Originally Posted by davis449 View Post
Quote:
Originally Posted by Red Bread View Post
Is there another half of TX I don't know about? Pretty sure it's all, or 90+% west of the Mississippi.
I was referring to the "half" of TX that serves primarily 91 octane as premium gas as opposed to the other half that serves primarily 93 octane as premium gas, therefore further negating the "West of the Mississippi River" generalization as well as your "Well, OK is 91" statement..
Half of TX uses 91? Honestly don't remember what Lubbock had when I was in college.
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      07-19-2017, 10:31 AM   #20
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Quote:
Originally Posted by Red Bread View Post
Really? My Father in Law lives there and I'd never noticed that. Guess that gives away that I don't really pay attention when on the highway.

I'm in Dallas and we have exactly zero ethanol free options. I'd trade 93 with ethanol for 91 with none all day. Stupid f'ing subsidies.
Ethanol increases the octane rating, so 93 with ethanol is better for producing power, but reduces your mpg.
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      07-19-2017, 10:46 AM   #21
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I remember it was very difficult to find above 90 octane in New Mexico and the western part of Texas. 91 was few and far between. This was 2006-2008 timeframe.
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      07-19-2017, 10:48 AM   #22
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Quote:
Originally Posted by smrtypants44 View Post
Quote:
Originally Posted by Red Bread View Post
Really? My Father in Law lives there and I'd never noticed that. Guess that gives away that I don't really pay attention when on the highway.

I'm in Dallas and we have exactly zero ethanol free options. I'd trade 93 with ethanol for 91 with none all day. Stupid f'ing subsidies.
Ethanol increases the octane rating, so 93 with ethanol is better for producing power, but reduces your mpg.
Higher octane doesn't create more power. Ethanol lowers the energy in gasoline. It's chock full of suck.
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