i don't see how a turbo car's intake changes the altitude....thats what im not understanding about what you say.

thin air is thin air, just because it is sucked into the motor shouldn't change it *THAT* much, should it?

 

I am not an engineer so I can't speak with authority, but my logic says that air pressure is what changes with altitude.

Since the turbo is creating 20psi of boost (hypothetically), the air pressure is 20 psi -- regardless of altitude.

 

i do see where you can assume that, but no where in the article do they say anything about altitude adjusting. they've simply said that when you have 87 at high altitudes, it will perform better in your car than it would in your car at sea level. they didn't say anything like:

and since this is true, in denver 91 octane is REALLY 87, they just label it 91.

but, that's why i've asked - i want to know if they do altitude adjust...and if they don't, then 91 is performing here as 93 and the 93 maps should work.

 

i just can't see that being the case - think of honda aftermarket turbos that only push like 6psi. does that mean the air pressure in their engines drops from 14.5psi (sea level air pressure) to just 6psi? that seems stupid. i think it's time to visit howstuffworks.com to solve this specific question.

 

from howstuffworks.com:

"The typical boost provided by a turbocharger is 6 to 8 pounds per square inch (psi). Since normal atmospheric pressure is 14.7 psi at sea level, you can see that you are getting about 50 percent more air into the engine"

do the math and they mean that you add the 6psi to the 14.7.

so if our atmosphere is only 12.2psi, and you add 6 to it, you end up with 18.2 - which is less than the 20.7 at sea level.

which means that even the air in the engine is different than it is at sea level and will effect the octane rating.

someone who knows the answer to this PLEASE RESPOND.

 

I don't believe that a boost gauge reads the difference, but instead the absolute pressure. This would mean that gauge that has been zeroed at sea level will read a slight vacuum at altitude.

My point is that, regardless of ambient air pressure, there is a set pressure created by the turbo -- say 20 psi. Granted turbo has to spin faster at altitude to create this pressure because the air is thinner, but the result is the same -- 20psi.


I agree that we need help

 

that sounds good too - but i don't know and i'm done speculating. i'll just wait till someone who know tells us. hopefully that will be soon.

 

interesting topic....any expert advise from Vishnu or Dyno?

 

i must be illiterate, because when i read this:

it is saying to me that they sell reduced octane fuel at the pump because of the difference in altitude. that isn't how you read it?

 

[QUOTE=gsujeff55]
Quote:
Originally Posted by evolute
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:

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.

it is saying to me that they sell reduced octane fuel at the pump because of the difference in altitude. that isn't how you read it?QUOTE]

all i know is in most sea level states, they sell 87, 89, and 93. here in denver most stations sell 85, 87, and 91. that tells me that they actually sell a lower octane, not that they try to pass it off as higher.

otherwise, the numbers on the pump would say 87, 89, and 93 like they do everywhere else, even though the actual gas would be lower in octane.

i don't really know, but that's my guess.

 

oh, ok. GOTCHA.

i didn't know the pumps read 85, 87, 91.

 

What I got out of the article is that they are allowed to sell lower octane ratings. But that the 91 octane here is the same as the 91 octane at sea level, it just acts differently at altitude. What gives me this impression is the last sentence in the article about taking a car with 91 octane from Denver to sea level. Just my .02.
**edit** The other thing that makes me think this is that if they marketed 85 octane as 91 octane, that would be considered false advertisement. Unless they had it clearly posted at the pumps that the fuel is "adjusted" for altitude. I've never seen a sign that states that.


As far as turbo motors go, JTB is correct. 20psi in a motor in Denver is the same 20psi in a motor at sea level. The difference is, is that the turbo has to work harder (spin faster) to make that same 20psi. This means that Evos in Denver will max out our stock turbos faster the stock turbo'd Evos at sea level.

 

ya, my head's been in the clouds - sorry

 

Ok boost gauges like the defi and autometer read differential pressure....while kavlico gauges like the ones used with AEM EMS and Zeitroniz Zt-2 read absolute pressure. I have both on my car and they read a 3 psi difference.