i've read that 91 octane here in denver (a mile above sea level) is the same as 93 octane at sea level.

if this is true, would a 93 octane map work in my car while i'm driving around here even though i'm running 91?

sorry if this has been covered - i was lazy and didn't search

 

bumpp

 

I'm in colorado Springs, and would really like an answer to this questions as well. the highest octane for sale here is 91, and I am running a 91 Octane map for DP and catback.

 

i'm pretty sure i have the magazine i read that in at home - i'll see if i can find it tonight.

 

that is a good question i didnt ever think of it that way i wish we got 93 that would b nice but hey maybe it technically is 93....... i got notning


evoisdream

 

this article was in the nov. 04 issue of import tuner - it's got all kinds of info. on pump gas, and this was one section:

"altitude check for all you hermits living out there: for someone living in at a high altitude, fuel sold at the pump may decrease to 84- or 85- octane. part of the ASTM gasoline regulations is any county 4,000 feet above sea level can reduce octane. engines at higher elevations don't need the higher-octane levels when compared to vehicles at sea level. fuel rules state that for every thousand feet above sea level, you are able to reduce the octane appetite by one number. conceivably, if you filed your tank up in denver and then loaded the car on a transport rig and towed it to sea level, the gas would detonate because of it's lower octane."

so, what this article says to me is that even though the recommended octane for the evo is 93, 91 is just as good when the evo is run at high altitude 'cus cars at higher altitudes require less octane. right? so can a 93 octane map work the same with 91 octane as long as it's at high altitude and not sea level?

 

We do have 93 here in denver. it's actually 93.5.....and the kicker is.......it is the same price as 91.

 

dude, where?!? which stations?

 

hahahah, thats crap. tellin me that they give you 85 octane and call it 91? cause that is what that article is saying. so no, if that article is correct, it isn't the same as 93, its actually eighty something and the height makes it equivelent to 91. that is a bunch of crap if you ask me.

 

sure, if they 'altitude adjust' the octane. i think what the article is saying is that 87 octane here is just the same as 87 octane at sea level...it's just that up here your car will run better on it since your car needs less octane to run correctly. so if you run 91 octane up here, it's the same 91 as they have at sea level, but your car will run as though it's on 93, even though it's not. that's how i read it anyway.

 

This is an interesting topic. I was under the impression that the turbo compensated for altitude as it spins more quickly in thinner air. This means that you are creating the same boost (approximately) at sea level and at altitude. Using this logic, there is no difference between the 2 as far as their tendency to knock. Unfortunately the logic for lowering octane needs as mentioned above would no apply to turbo charged cars as they create their own atmosphere, and hence we could be actually running on 85 **** octane gas.

This is just my logic and cannot back this up. Someone please tell me I am wrong!

 

no, thats not the way i read it.

they are already compensating for the altitude...you will be compensating the gasoline again......

see what im saying?

 

no, because you are still burning the super thin air.....it applies to turbocharged cars just as much as NA cars. but, them giving you 85 octane makes the car *think* it has 91 octane due to the altitude.

by that reasoning, it is still 91 octane, if not worse....

so, learning from this, don't drive your car out of denver towards the plains without refilling as often as possible, and dont think you have 93 instead of 91 because of the altitude, think that you have 91 instead of 85 because of the altitude.

if that article is correct, id be pissed!

 

Let me rephrase.

1) Altitude increases the effective octane rating of gas.
2) Since the turbo is creating the same environment in the combustion chamber at either sea level or altitude, the altitude is irrelevant. – turbos spin faster in thinner air and create the same boost.
3) If altitude has no effect on octane ratings in regards to turbo charged cars then I am really hoping that the octane rating on pumps is not "adjusted" for altitude!

Am I correct?

 

I didn't know that altitude had no effect on octane ratings on turbo cars.....