Yes the 91 vehicles have o2 fuel system to adjust air fuel ratio while driving. So if it calls for 91 unless it's just horrible I wouldn't switch to 87. The guys running the 87 machines seem to also have issue at high altitude when running 91 or higher. But that engine was low compression so then when you add low oxygen to slow burning fuel it caused issues.

Sent from my SM-S908U using Tapatalk

 

I have to argue a bit with Ace on this. When a manufacturer recommends a fuel grade, unless otherwise stated, it's for sea level (or close) applications. You just build so much more pressure in the cylinder at sea level than you do at 9200 ft. (it's why turbos and superchargers help so much at altitude and are used on many piston driven plane engines) Since you are nowhere near sea level pressures, you can drop down in grade of fuel safely. I run at 6000 feet a lot and I never need over 89 in anything I own except for my Torino at 11:1...and that includes my twin turbo bmw. I never detonate. Have you noticed that (other than the swill they sell in California and Arizona) that premium is 93 octane at sea level locations...yet is only 91 at altitude? That's because it isn't necessary. You can try stepping down a grade. You will notice if it detonates. I will be shocked if it isn't just fine. Keep in mind the higher the octane, the slower it burns. With your loss of cylinder pressure at that altitude, a quicker burn will help.

Ace...what the heck is an O2 fuel system?? Are you saying it adds O2??

 

He's referring to the systems that incorporate an oxygen sensor. Some call it an air/fuel ratio sensor.

 

Ahh... That adjusts the a/f ratio regardless of altitude...but has nothing to do with octane requirements.

 

Lol yes

Sent from my SM-S908U using Tapatalk

 

Thx guys. Will keep that in mind.

 

I used to ride my sleds at those kinds of altitudes. I would wonder who stole my engine...