Quote:
Originally Posted by smbstyle
I may be relocating out to the Denver area for work shortly (from FL; I get cold when it's under 70* here...), and am wondering from those who have moved from a sea-level area out to Colorado; is there a noticeable drop in performance in the car?
Car isn't too powerful as it is; I'm wondering how bad it is a mile above sea level and up through the mountain highways.
Good to hear that people are able to drive this car out there; I was considering selling mine for a STI or something b/c I wasn't sure how it would fair out there.
Oh, and one more question - is 93 octane readily available out there?
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The air density is roughly 20-25% less, so you will certainly lose power. It's not massive, but it's noticable. You will get used to it, though.
A turbocharged engine (such as in the STi) still suffers, but less so because it compresses the air a certain amount beyond ambient. So the relative loss is more like 12-15% I believe...
Quote:
Originally Posted by Chupacabra
Hello, I did notice a slight drop in power (probably the elevation) for a few weeks. My ECU seems to have adjusted to the difference in thinner air. Even though I most recently lived in MN, my car has been to the south a few times.
Also, there most places in the suburbs only offer 91 as the max octane. According to a few of my coworkers there is a place selling higher octane fuel, but it isn't cheap. I think he mentioned that the state believes the thinner air equates to 'not needing a high octane'.
I'll let you draw your own conclusions on that.
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The ECU may be able to tune more aggressively within it's tables due to the reduced ambient air pressure at altitude, but this is just a guess. A better explanation is that you probably noticed a huge difference at first, but have simply become accustomed to it over time.
Your coworkers are correct, the altitude is exactly why 91 octane is commonplace. When the air/fuel mixture is compressed, it heats up very rapidly and can cause hot spots resulting in dangerous preignition (detonation, ping, knock). That's when the mixture ignites itself before the spark tells it to. At higher altitudes there's fewer air molecules per volume of air, so less heat is generated when it's compressed; there's fewer air molecules to rub together. Higher octanes are simply better at resisting preignition. So, since there's less heat, you don't need as much octane to stabilize the mixture against preignition.