Why do many WEST states have MAX of 91 Octane?

[sleddriver]

Originally Posted By: Astro14
As an aside, nothing was more fun that taking my shoe-box shaped Volvo 240 turbo wagon into the mountains. Its measly 165 BHP wasn't competitive with a lot of cars at sea level...but once you got to 10,000 feet, the normally aspirated Corvettes and Porsches (at the time) were making even less as they wheezed along in the thin air and I took great satisfaction in passing them on mountain roads...

Felt the same way back in the days of having the '85 SAAB 900T. You can't beat having boost + fuel injection + 5-speed when driving the mountains. Repeatedly enjoyed that car's combination while driving through several mountain states & teritories on my big round trip.

 

[DriveHard]

Originally Posted By: javacontour
Well, it's higher than STL.

Humidity? Does that play a role as well. Dry, less dense air?

Originally Posted By: tempnexus
Even in Phoenix AZ? I mean they are not that high above the sea level.


Dry air is more dense than humid air. Seems counter-intuitive, but it is true.

 

[BMWTurboDzl]

Originally Posted by 440Magnum
Elevation- lower air density means lower cylinder pressure, which means lower octane requirements.


IIRC That is largely no longer the case due to the fact that the vast majority of engines sold today are turbocharged which can compensate for altitude.

 

[dave1251]

Originally Posted by BMWTurboDzl
Originally Posted by 440Magnum
Elevation- lower air density means lower cylinder pressure, which means lower octane requirements.


IIRC That is largely no longer the case due to the fact that the vast majority of engines sold today are turbocharged which can compensate for altitude.



No most engines sold are still normally aspired and if premium fuel is recommended it's recommended at 91 octane.

 

[c502cid]

Originally Posted by Benzadmiral
In Denver (el. 5280 ft.) we had 85, 87, and 91 octane -- this in the late '90s. I was buying 91 for my 420SEL when a member of the local MB Club told me that even on the older cars without a knock sensor, the midgrade 87 worked fine. I tried it and had no power or other issues. When I set out to come back to NO, I made sure to fill up with the 91 before I dropped down out of Raton Pass and drove at lower elevations.


It was worse in the 80's, the Denver metro had 85, 87, and 89 as the top octane. However, we still had Sinclair selling leaded premium! I pumped gas at a Sinclair station all through college back then, we had every hot rod and Harley in town come in.