esr5096

I was away last weekend and stopped for gas, was surprised to see Sunoco 91 at that station. Then today, the one near me had 91 too, and no 94, they had 87, 89, 91, and 93. Didn't all the sunocos used to have 87, 89, 93, 94 in the northeast? Has anybody else notcied this change?

DEVO

91 octane gas in DENVER acts the same as 93 octane gas at sea level... so you don't want to put 91 octane gas in at sea level... the reason that you find 93 in most stations is because we live in areas where one day you can be at sea level and the next day you are in the mountains. So 93 works well at higher altitudes and it works right at sea level... hence you find 93 at most gas stations....


if you live in the mountains... 91 is all you need.

esr5096

who says you need 93 at sea level and 91 in other areas? The owner manual (and dealer) both just say 91.

DEVO

read above statement... i did some more research.

so another way of reading this is, 93 octane gas at SEA LEVELl acts like 91 at high altitudes.

jcg878

But isn't it far more likely that the need for a 91 octane rating is determined closer to sea level than in 5000 foot elevations? Hence, if you live in the mountains, then 89 is all you need by your logic, right?

DEVO

it's confusing i agree but you need more octane closer to sea level... the reason is that there is more air at sea level than at higher altitudes so you don't need octane to retard combustion, the lack of air is doing that for you.

plus you are in a sense making gas less explosive the more octane you put in... so you are robbing some of the power away from the gas.


ALSO... the keyword in my statement is ACT... so I'm not saying they are equal... because they are not.


Another way to look at this is that you are actually worst off by putting in 93 octane in Denver then by putting in 91.

The counterpoint would be that putting 107 (racing fuel) in your car at sea level is worst then putting in 93. In order to take advantage of 107 fuel, you need to increase the compression of your engine... which isn't easy to do.

By worst I mean that you are not gaining any performance advantage and could actually lose performance.

jcg878

I understand what you're saying about how the same octane rating can act differently at different altitudes. I'm just saying that the engine was likely tuned/designed at an area nearest sea level, and therefore all you need if you don't live in the mountains is 91. Another way of saying this is that you need 91 octane at sea level, and less than that at higher altitudes (rather than 93/91).

I'm just debating for the sake of discussion. Only 93 is available around here, so that's what I use.

DEVO

no problem.


91 at sea level is probably good enough but chances of you finding 91 at stations near the sea is unlikely.

93 is needed at sea level because there is more atmosphere at sea level then higher in the mountains.