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Pre-detonation and octane levels at higher elevations?

SteveSS

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I've often wondered how our high elevation, I've at 7500' and most of Colorado Springs is 6000' or over affects our engine performance. I've taken some modern high-performance cars down to lower elevations and the performance very noticeably increased. I know our compression is much lower here due to the thin air. At the pump, the highest octane we can buy is 91.

I watched an Engine Masters show where they ran everything from different pump gas octanes up through E85 and Methane in an engine and it didn't make much difference in HP. Right now 91 unleaded is about a buck more a gallon. Right on my gas cap, it says to use premium. Do I really need it? Does our elevation, therefore lack of compression, change things? Like is pinging worse at 7500' than 1500'? I'm not sure I would know what to listen for.
 
Snowmachine industry seems to think that there is a 3.5% HP loss per 1000' elevation gain for naturally aspirated engines . Am at 7300' and there is definitely a substantial loss .
 
Elevation does affect for sure. We are anywhere from 5200' to 6000' here in Albuquerque. I know when I moved here from Missouri I had to take 2 jet sizes out (lean)of my carb so it wasn't so rich, ran better afterwards also. If I go to Roswell to race (3200') I add a jet to my carb. I saw that Engine Masters show, I think they finally said something in regards to the timing, once you have optimum setting it doesn't make any difference what the octane was as long as it did not ping. Even more octane than needed didn't hurt the performance. Not sure what year your car is, but the octane rating on the gas cap is for best performance. I would think that if octane was too low and it started to ping, the anti knock sensor would tell the computer to back timing down, which would lower performance of the engine.
 
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