SwedeSpeed - Volvo Performance Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter · #1 ·
Im shure i cant find this one in my owners manual. I was told by the dealer to use 87 octane because it will run better in altitude then 91. I live at 9000' is this true?
 

·
Registered
Joined
·
7,600 Posts
Re: Altitude and octane, how do they relate? (DazedandConfused)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>DazedandConfused</b> »</i></TD></TR><TR><TD CLASS="quote">Im shure i cant find this one in my owners manual. I was told by the dealer to use 87 octane because it will run better in altitude then 91. I live at 9000' is this true?</TD></TR></TABLE><p>Altitude definitely has an impact on octane requirements... according to the <A HREF="http://www.eia.doe.gov/oil_gas/petroleum/data_publications/wrgp/gasoline_grades.html" TARGET="_blank">EIA</A>:<p>"In general, automotive octane requirements are lower at high altitudes. Therefore, in some areas of the United States, such as the Rocky Mountain States, the octane ratings for the gasoline grades may be 2 or more octane points lower. "<p>UKMatt
 

·
Super Moderator
Joined
·
9,305 Posts
Re: Altitude and octane, how do they relate? (DazedandConfused)

If you ran a 2.4i, I would agree. With a T5, I guess I semi-agree. The reason why it's not true is that the turbo pressurizes the intake, negating the low ambient pressure. The reason for the "semi" is that it's a low-pressure turbo, and also is not providing boost at low rpm's or when crusing under light load. So, perhaps it comes out somewhere in the middle.<p>I guess I'd suggest giving it a try in your car, and see what you find! Let us know if you do, I'd be interested anyhow.<p>Tom.
 

·
Registered
Joined
·
345 Posts
Most of that "rule of thumb" originates from old carbuerated engines. The lack of o2 due to lower density air made the mixture rich. A rich mixture is less susceptible to detonation... hence the lower octane requirement in higher compression engines at higher altitudes (whew, that was a mouthful!)<p>With o2 sensors and fuel injection, not to mention variable valve and ignition timing... most engines can take o2 density into account. You're better off running the octane the manufacturer calls for.
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #6 ·
I just got back from the gas station up here, its a new station and they sell 85! down in the valley its all 87. There must be some truth to all this, this has nothing to do with the responces recieved on this thread, just a observation.
 

·
Registered
Joined
·
3,028 Posts
Re: (DazedandConfused)

<br>Assuming the t5 works on absolute pressure (most turbo setups) meaning the turbo works harder to make up for the lack of ambient pressure, meaning that there should be the same or greater need for octane. This would be under most medium output conditions and all WOT conditions.<p> On a NA engine lack of ambient pressure means less filling of the engine means less effective CR means you can get away with less octane and of course less power both from the lack of effective compression and from the lack of air ingestion, of course this would come into play only at near WOT conditions.<br>
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #8 ·
thanks! is there section of this site that explains acronyms? <IMG NAME="icon" SRC="http://www.vwvortex.com/vwbb/biggrin.gif" BORDER="0">
 
1 - 8 of 8 Posts
Top