What's the deal on 85 octane?

[Joe Bob]

Since I am now a CO resident....can a 3.6 (MY 91) handle that low an octane?

[Bob Kontak]

I think the car has to be built to accept it. Yours ain't.

[kenikh]

Your knock sensor will be banging so hard, you'll wonder what hit you.

85 octane??? Didn't even know that existed. Is it made from the heads and tails of moonshine?

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[darrin]

joe bob -- did your 3.6 run properly on 87 octane at/near sea level? Octane requirements decrease as altitude increases. So, here in Colorado at 5k feet, 85 octane has equivalent antiknock properties as 87 octane at sea level.

Put another way, in colorado, "regular" gas is 85 octane -- and is used by cars that don't require premium fuel. Since my stock 3.2 requires premium fuel, I fill up with 91 octane premium.

Oh, and welcome to colorado!

[Luccia at Pelican Parts]

Whoo-hoo! Welcome! I've always put 87-91 in all my vehicles in Colorado and personally tend not to really mess with 85. I see you're in Erie, hope you take the time to visit IMI out there! I looooove taking their shifter karts out around the track.

[Shaun @ Tru6]

How did you get to CO and are wiener dogs safe at that elevation?

[Lukesportsman]

Don't travel to Laramie, WY with a turbo, hi-comp, supercharged car. Last time I was out there....and yes it's higher than Denver by about 2000ft. 85 octane was the ONLY gas stocked! Luckily the rental did fine, but I was caught off guard and it made me chuckle.

[Matt Monson]

Originally Posted by darrin

joe bob -- did your 3.6 run properly on 87 octane at/near sea level? Octane requirements decrease as altitude increases. So, here in Colorado at 5k feet, 85 octane has equivalent antiknock properties as 87 octane at sea level.

This. The altitude is basically like picking up 2 points. I put 85 in my 2016 Outback and my 2016 Frontier. I put 87 in the Boxster and the AC 911s. Only my 11.2:1 CR Subaru needs 91...

[uwanna]

Joe Bob, I believe with a 3.6 motor at 11.3 to 1 compression, I would stick with at least 91 octane which PAG calls for at a minimum. Yes, knock sensors can help with marginal octane fuel, but they also retard timing which reduces performance potential markedly.

[2.7RACER]

As a long time resident of Albuquerque at 5000 feet or greater elevation we have been dealing with the lack of oxygen as compared to sea level. The rule is 3% loss for every thousand feet above sea level. This results in a 15% loss to the effective compression ratio. For an engine rated at 10:1 compression, the loss is 15% resulting in a net compression ratio of 8.5:1. With this lower effective compression ratio the requirement for higher octane fuel is not needed. Of course when travelling to lower elevations put in higher octane fuel.

[Koizumi]

Dang I didn't know you moved from SoCal!

[tobluforu]

There have been many debates in regards to whp on dynoes between people living in co and higher elevations, and people at sea level. Kind of silly if you ask me, but man do some people fight about it on different boards.

[Joe Bob]

Originally Posted by Shaun @ Tru6

How did you get to CO and are wiener dogs safe at that elevation?

The kids are still in CA. I will fly back and pack my tools, graphics and clothing and travel slowly back with a rental truck and the wieners.....I got here in 19 hours driving straight thru with my nephew in the Porsche.

Just never seen 85 octane outside of Mexico. I MAY try a tankful and see what happens.