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13282 Views 9 Replies 6 Participants Last post by  GARYD
I have a question on octane ratings. I live in Colorado where 'regular' gasoline has an 85 octane rating, I think due to our higher elevations. Everywhere else I've been to in the US 'regular' gasoline has an 87 octane rating. Here 87 is 'midgrade. I know the owners manual says to run 87 in the 2011 Terrain. I've only run 1 tank of the 85 octane fuel that I filled at 1/2 a tank and don't appear to be having any knocking. I assume this gives me an approximate octane rating of 86. What will be the effects of running 85? If I start getting knocking and pinging will using the higher octane rectify the issue?
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yup...if you have issues, just up the octane....theres less oxygen in the air up there, which is why they done need the gas as combustible...

United States: in the Rocky Mountain (high altitude) states, 85 AKI is the minimum octane, and 91 AKI is the maximum octane available in fuel[citation needed]. The reason for this is that in higher-altitude areas, a typical naturally-aspirated engine draws in less air mass per cycle due to the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill up a carbureted car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine. A disadvantage to this strategy is that most turbocharged vehicles are unable to produce full power, even when using the "premium" 91 AKI fuel. In some east coast states, up to 94 AKI is available [1].
That was fast and thank you for the info. Most of the driving I will be doing will be here in Colorado. I guess by the time I get to sea level I will be running 87 anyway.
I doubt if you will get any knocking since the knock sensor will adjust to it, but if you do, just go up to the next octane.
Just so everyone is clear HIGHER OCTANE makes gas LESS combustible not more. If you have knocking and the car is designed for 87 and you are running 87 the issues IS NOT the gas. It is a knock sensor, fix the problem don't cover it up with duct tape. The computer may need a little time to adjust but it should account for the altitude and octane in your car.

Also - people who think they get more power putting 93 in a car designed for 87 usually are not. Except in a few cases where the car can actually use 93. (Honda Accord V6 is one engine that can.)

For the most part more octane is money down the drain.
Last Sundays Chicago Sun Times auto section there was a review on the new Hyundai Equus. Here is a little part of that review. I got this off the Sun Times web site.

Unlike some rivals, Hyundai plans no long-wheelbase version of the Equus because it feels extra rear seat room isn’t needed.

The Equus has a smooth, quiet 4.6-liter dual-overhead-camshaft, 32–valve V-8 with continuously variable valve timing and a variable induction system. It develops 385 horsepower
on premium fuel and 378 horsepower with regular fuel.
[/color] The 0-60 mph time is 5.7 seconds.

City fuel economy is not impressive, an estimated 16 mpg, while the highway estimate is 24 mpg.

The engine works with a responsive six-speed automatic transmission with a manual sport mode.
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Not sure which side of the fence you are on, but it appears that the Equus engine was "designed" for Premium fuel, but will also run on regular fuel. On regular, they will retard the ignition timing, resulting in less power. However, if an engine is designed for Regular fuel, like the Equinox/Terrain, then running on Premium fuel will not allow the computer to advance the timing and produce more power than the quoted HP.

I suppose that if your GM engine would ping on regular, then the knock-sensor will dial back the timing and decrease the HP from the quoted HP. Then, using the higher octane fuel could get it back to rated HP, but I don't see it ever getting above rated HP with a higher octane fuel.
RITT333, we're on the same page.
Some people think you can't use regular gas in a car that's advertised as using premium gas.
If the manual says "REQUIRES" premium then you need to use premium.
If it says "RECOMMENDS" then you can use regular also.
RIT333 said:
On regular, they will retard the ignition timing, resulting in less power.
Yep, retards timing to prevent engine knock.

GARYD said:
If the manual says "REQUIRES" premium then you need to use premium.
If it says "RECOMMENDS" then you can use regular also.
Yep again. Hyundai obviously plays with timing and/or other factors to prevent knock on regular, at the cost of slightly less power. And trust me, nobody will notice the loss of 7 HP, it's less than 2%.
Yep, I've never noticed it in my Vettes and Harleys during everyday driving. On the strip or course I did use premium though.
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