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low octane at high elevation

Gil Bang
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Gil Bang

Gil Bang 25918

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I was up at Zion, and noticed that "regular" gas there is 85 octane, and "mid-grade" is 87.  High was 90.

Somebody said that at high altitudes, lower octane works fine, but I used the 87 anyway (which is "regular" in CA.

 

What's the story?

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iamthepush

iamthepush 72

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Cars that require high octane have high compression engines. If you use 87 in a car that requires 93 you run the risk of pre-ignition (might burn hole in piston).

I don't know for certain but I think since the air is less dense (less o2) 90 octane at 6,000' is the same as 93 at sea level.

The car's knock sensor listens for engine ping, and will retard the timing if any it's detected.

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iamthepush

iamthepush 72

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Most cars now have turbos or superchargers. If you have any forced induction it doesn't make a shit at all.
Are you retardation?

A- most cars today are naturally aspirated

2-If you have a supercharger or turbocharger you have a high compression engine.

God, you're dumb

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immamac

immamac 42835

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https://cars.usnews.com/cars-trucks/cheapest-turbocharged-cars

Super weird. It's almost like anyone who wants good fuel economy has FI.  Ecoboost from Ford. Eco from any vendor. Most Subaru have a small turbo. Its weird how stupid you are even the damned Chevy sonic has a turbo. 

This isn't 2010, you are the stupid one. Its not for performance anymore its for fuel economy. Shut the fuck up about things you don't know about and save yourself some embarrassment next time. 

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iamthepush

iamthepush 72

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https://cars.usnews.com/cars-trucks/cheapest-turbocharged-cars
Super weird. It's almost like anyone who wants good fuel economy has FI.  Ecoboost from Ford. Eco from any vendor. Most Subaru have a small turbo. Its weird how stupid you are even the damned Chevy sonic has a turbo. 
This isn't 2010, you are the stupid one. Its not for performance anymore its for fuel economy. Shut the fuck up about things you don't know about and save yourself some embarrassment next time. 
Does it hurt being so dumb? Most cars on the road are N/A. Sure MAYBE 51% of 2021 models might have a turbo/S/c,

And where the fuck have you been? When the Chevy Sonic came out in 2012 you could get a 1.4 turbo.

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deadshank

deadshank 24652

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35 minutes ago, immamac said:

https://cars.usnews.com/cars-trucks/cheapest-turbocharged-cars

Super weird. It's almost like anyone who wants good fuel economy has FI.  Ecoboost from Ford. Eco from any vendor. Most Subaru have a small turbo. Its weird how stupid you are even the damned Chevy sonic has a turbo. 

This isn't 2010, you are the stupid one. Its not for performance anymore its for fuel economy. Shut the fuck up about things you don't know about and save yourself some embarrassment next time. 

I thing politics in the DT is really starting to wear on Immamac. 

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XYZ

XYZ 2154

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2 hours ago, immamac said:

Most cars now have turbos or superchargers. If you have any forced induction it doesn't make a shit at all.

What do you mean by “it doesn’t make a shit at all”? You mean that the fuel octane doesn’t matter with forced induction engines?

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High Plains Drifter

High Plains Drifter 11029

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On 5/29/2021 at 2:44 PM, iamthepush said:

Cars that require high octane have high compression engines. If you use 87 in a car that requires 93 you run the risk of pre-ignition (might burn hole in piston).

I don't know for certain but I think since the air is less dense (less o2) 90 octane at 6,000' is the same as 93 at sea level.

The car's knock sensor listens for engine ping, and will retard the timing if any it's detected.

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23 hours ago, Parliament said:

Thinner air -> less O2 -> low octane OK

 

 

We just bought a 2006 Volvo that has an inline 5 engine with turbo. Takes the high octane gas. But we live at ~5,000 ft elevation, so y'all are telling me I could be putting the mid-grade in it?

 

 

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TwiceHorn

TwiceHorn 31438

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2 hours ago, High Plains Drifter said:

 

 

 

 

We just bought a 2006 Volvo that has an inline 5 engine with turbo. Takes the high octane gas. But we live at ~5,000 ft elevation, so y'all are telling me I could be putting the mid-grade in it?

 

 

I wouldn't.  It's asking for trouble.

Two things make an engine susceptible to detonation or knocking, high compression ratio (>9.0) and forced induction.  They often go together, but don't have to.

Both raise the energy state of the fuel-air mixture in a combustion chamber to a level where it is more likely to to explode before ignition.

Knock sensors seemed to be pretty effective at reducing/eliminating knock in high-compression engines, so you were safe with a non-turbo using lower octane gas with some performance or mileage hit.  That doesn't seem to be reliably true with turbocharged engines.  A goodly number of turbo engines have detonation-related failures and it's often traced to using lower octane fuel.  Synthetic oil seems to have some positive effect on reducing detonation, also, apparently because they outgas fewer volatile fractions or molecules that can contribute to detonation.

Finally, air is less dense at altitude because of lower atmospheric pressure.  A turbocharger or supercharger exists to raise the air pressure above atmospheric (they were essentially invented to make piston engines run well at altitude on aircraft), so the notion that there isn't enough O2 to cause detonation at altitude is suspect.

Small addendum.  It looks like lower octanes are or were standard at high altitudes because high octane fuels can actually make an engine hard to start at high altitudes and were satisfactory running in the lower-O2 environment.  I'm not sure that latter part holds completely true anymore with more modern engines.

Edited by TwiceHorn
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Parliament

Parliament 14242

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2 hours ago, High Plains Drifter said:

 

 

 

 

We just bought a 2006 Volvo that has an inline 5 engine with turbo. Takes the high octane gas. But we live at ~5,000 ft elevation, so y'all are telling me I could be putting the mid-grade in it?

 

 

Use whatever the owners manual says.  Don't make this a thing.

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iamthepush

iamthepush 72

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, so y'all are telling me I could be putting the mid-grade in it?
 
 


If you want the privilege of maybe having to buy a new engine.

Curious, what part of my post led you to believe that you could put mid grade in it? What octane is mid in your area?

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High Plains Drifter

High Plains Drifter 11029

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15 hours ago, iamthepush said:




Curious, what part of my post led you to believe that you could put mid grade in it? What octane is mid in your area?


 

 

 

On 5/29/2021 at 2:44 PM, iamthepush said:



I don't know for certain but I think since the air is less dense (less o2) 90 octane at 6,000' is the same as 93 at sea level.






 

 

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conVINCEd

conVINCEd 21469

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We stopped at the same gas station in Raton, NM to get the timing adjusted on my grandpa’s motorhome every time we went skiing when I was a kid.  One year he got a new motorhome and we didn’t have to stop anymore.  Thought that might be relevant.  

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