patperry2766 wrote:
For clarification's sake, I did buy the 85 octane. I could tell a difference but it's hard to differentiate exactly how much of a power loss because of the altitude vs fuel. I did do a considerable amount of driving without the trailer and I really couldn't tell much of a difference in either fuel economy or performance that couldn't be attributed to the elevation.
However, once I got back to Texas and out of the mountains and 87 fuel in Amarillo, I could tell a significant improvement in performance. I've made multiple trips to the mountains of CO and SD in the past and always bought the cheapest gas available without paying much attention. I honestly don't know why I noticed it this time, but I've got over 100K miles on my truck and have had no issues what's so ever based on my fuel.
I guess for my own peace of mind, next year, I'll try the 87 in the mountains to see if I can tell a difference.
It was altitude, not the fuel. 85 in CO runs the same as 87 in Armadillo.
SD doesn't have mountains lol..... I wouldn't be thinking 85 down there, but then again I don't think they sell 85 in SD, although I've only bought diesel there in the last 15-20 years.
For an engine (we're talking newer NA, engines that adjust timing based on multiple parameters) designed to run on 87, I'd keep with that for max performance up to around 5000' min. Above that, 85 will do the trick.
Depends how the vehicle is calibrated though. This isn't 1 size fits all generality.
For example, the 6.2 fords I had, couldn't tell the difference. But our old 06 SRT 8, near sea level is a turd on 87 and a rocket on premium. Road trip down the freeway, she drinks 87. Anywhere I want to use the throttle, gets 91.