Octane at higher elevations

kp1xx1 said:

These types of threads get wild and I am reluctant to chime in because there are always many, many experts on these topics.  With that said, take my simple statements at your own risk.  I will state that my profession is the design of engines that many of you probably own.

Knock and detonation are a result of cylinder temperature.  Temperature is defined by a number of things including ambient air temperature, geometric compression ratio, engine load, etc.  Temperature in a IC engine changes as the volume of the cylinder changes and as thermodynamic processes (combustion) take place.  Octane (although not really a great indicator) is a rating of a fuel's ability to resist combustion.  There is a direct relationship between the Octane number and the energy required to start combustion.

Its important to understand there is a difference between knock and pre-detonation.  An ECU can pick-up pinging (knock) and make adjustments to attempt to deal with that.  The quickest method is to pull out timing.  On most modern engines it works pretty well.  If an engine experiences true pre-detonation, which is uncontrolled combustion as the result of high pressure waves that snowball on top of one another, there is nothing to be done, it runs away in fractions of a second and will destroy your engine.  No amount of timing adjustment will fix that.

Something one may find interesting is that many of today's turbocharged gasoline engines run on the knock line constantly.  They only make rated power on premium fuel and under WOT conditions are constantly mitigating knock.

All of that said, the general theme in this thread is correct; that at higher altitudes, cylinder temperatures (and hence pressure) will be lower and the required octane to prevent engine damage is reduced.  It is also true premium fuel is called premium not really due to its octane rating, but because it is of much higher quality.  As some mentioned in here, buy the best fuel you can afford.  It doesn't hurt!  I've ran Tecumseh snow blower engines on race gas left over from the summer.  No difference in operation other than the exhaust had an awesome aroma!

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Sprucegum said:

My 2017 ford operator?s manual says I can use regular fuel and recommends I buy a tank of pr emium occasionally. How often is that? Are they making this recommendation to clean out any building up?

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I believe your manual says this:

Your vehicle is designed to operate on
regular unleaded gasoline with a minimum
pump (R+M)/2 octane rating of 87.
Some fuel stations, particularly those in
high altitude areas, offer fuels posted as
regular unleaded gasoline with an octane
rating below 87. We do not recommend
these fuels.
For best overall vehicle and engine
performance, premium fuel with an octane
rating of 91 or higher is recommended. The
performance gained by using premium fuel
is most noticeable in hot weather as well
as other conditions, for example when
towing a trailer.  See
Towing (page 257).

The Theory they tell me is the "Thinner" air at Altitude does nto need the same level of Octane

My Engine said "OH YES I DO".

Larry N. said:

Interesting. Did you buy the mid-level (or premium) gas then when refueling at high altitude stations (4,000' and above) in order to still get 87 octane? Everywhere I've been in Colorado and Wyoming (and New Mexico) regular is 85 octane, so I'm curious how you maintained that 87. And, as Lou mentions, lower octane works fine at higher altitudes to give the same anti-knock properties in a normally aspirated engine.

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In the midwest and places where I run into 85 octane I run 85 octane.  Whatever is the lowest.

lynnmor said:

I believe your manual says this:

Your vehicle is designed to operate on
regular unleaded gasoline with a minimum
pump (R+M)/2 octane rating of 87.
Some fuel stations, particularly those in
high altitude areas, offer fuels posted as
regular unleaded gasoline with an octane
rating below 87. We do not recommend
these fuels.
For best overall vehicle and engine
performance, premium fuel with an octane
rating of 91 or higher is recommended. The
performance gained by using premium fuel
is most noticeable in hot weather as well
as other conditions, for example when
towing a trailer.  See
Towing (page 257).

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and,  I said the same thing as the Ford manual ... 

Premium fuel does make a difference.

Question.....How do they make different levels of octane gas?

I know a truck driver who transports gasoline and he says it all comes out of the same tank and they add things to it when they fill his tanks..

So is more of something added to the basic gasoline to raise the octane level?

lynnmor said:

If an engine has a turbocharger, there is little change in pressures at higher elevations, so the same octane should be used at all times in those engines.  The idea that the ECU can adjust for low octane is not entirely true, because detonation from pressure has nothing to do with ignition timing.  The adjustment in timing will decrease power and mileage and is done in an effort to protect the engine from poor choices of fuel.  If all else fails read the manual, there is a lot of incorrect information in this thread.

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Which is why I said, "lower octane works fine at higher altitudes to give the same anti-knock properties in a normally aspirated engine." (emphasis added)

Larry N. said:

Interesting. Did you buy the mid-level (or premium) gas then when refueling at high altitude stations (4,000' and above) in order to still get 87 octane? Everywhere I've been in Colorado and Wyoming (and New Mexico) regular is 85 octane, so I'm curious how you maintained that 87. And, as Lou mentions, lower octane works fine at higher altitudes to give the same anti-knock properties in a normally aspirated engine.

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Larry, yes that is basically what I did after discovering the issue I added some premium fuel to bring up the average octane of the remaining fuel in the tank, then until heading back home to sea level (sea level-ish it is 240 ft above sea level at my house) opted for the mid grade if the base grade was 85 octane, or used the base grade if it were 86 octane.

Ike

p.s. that should be retard timing for altitude, as advancing timing is used to get more horse power, but requires higher octane.

Arch Hoagland said:

Question.....How do they make different levels of octane gas?

I know a truck driver who transports gasoline and he says it all comes out of the same tank and they add things to it when they fill his tanks..

So is more of something added to the basic gasoline to raise the octane level?

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The octane level of the gasoline is established in the blending at the refinery, they blend for a number of different traits, often re-blending if a batch is off on one thing or another.  I live in SW Louisiana where there are many refineries, and have an old friend that worked in the lab at one of them back in the 90's, he tells stories of hating the then newer low emissions gasoline blends like RFG because the blend tolerances were so much tighter than the old stuff, so batches would often have to be reblended multiple times to meet specs.  What your driver friend was likely talking about was the detergent packs for each name brand of gasoline, which get added in when the trucks are loaded at the depot.

So in other words you may have an area where all the gasoline comes from the nearby Shell fuel depot, regardless if it is going to an Exxon station, or a Citgo Station.  It just gets Exxons proprietary detergent blend pack added in when it gets loaded into the truck to be hauled to the Exxon station.

Isaac-1 said:

The octane level of the gasoline is established in the blending at the refinery, they blend for a number of different traits, often re-blending if a batch is off on one thing or another.  I live in SW Louisiana where there are many refineries, and have an old friend that worked in the lab at one of them back in the 90's, he tells stories of hating the then newer low emissions gasoline blends like RFG because the blend tolerances were so much tighter than the old stuff, so batches would often have to be reblended multiple times to meet specs.  What your driver friend was likely talking about was the detergent packs for each name brand of gasoline, which get added in when the trucks are loaded at the depot.

So in other words you may have an area where all the gasoline comes from the nearby Shell fuel depot, regardless if it is going to an Exxon station, or a Citgo Station.  It just gets Exxons proprietary detergent blend pack added in when it gets loaded into the truck to be hauled to the Exxon station.

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I'm trying to understand the difference in 87, 89 and 91 octane and how they achieve it.

So are you saying they make a batch  87 octane and place it in a ginormous tank labeled 87 octane and then make another batch and put it in another ginormous tank label 89 octane and so on? 

And so then the tanker truck would fill up a specified octane at a specific  tank, add whatever miracle cleaners that the receiving  gas station wanted  and deliver that load.

Is that correct?

Story.. Friend was watching the delivery driver at a Standard Station (Remember those) one winter.  He pumped the gas. Then read the meter, then got a bunch of HEET brand gas line antifreeze out and added it to the station's tank.  (My Advice sir. Get De-Icer.. Remember those ads?)  I can tell you .. GOOD ADVICE.. More stories on request.

Same with Octane. there are "Octane boosters" normally added at the refinery and it does come out of different storage tanks.  But no reason they can not be added later.

John From Detroit said:

Same with Octane. there are "Octane boosters" normally added at the refinery and it does come out of different storage tanks.  But no reason they can not be added later.

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okay, I didn't major in Math....but according to my math, 

the average bottle of Octane Booster from Walmart was around $4.00 for a bottle that treats 15 gallons. 

that came out at .26 cents a gallon.      So why not just buy Premium at the pump for usually a .20 +/- cent a gallon increase  ???

Back in what I now refer to, semi-fondly, as my Massively Misspent Youth, I used to pump gas part time while going to college.  Yes, there are separate tanks in the ground, and the tanker trucks that delivered fuel were not one big tank, they had several internal tanks.  We would 'stick' the tanks with a 12 foot long wooden ruler, marked off to every half-inch, and we had a chart that would convert the 'stick' reading to remaining gallons.  We would then order X gallons of Regular and Y gallons of Hi-Test, and the same tanker truck would bring both products for us.

Sunoco used to have pumps that custom mixed fuel.  Sunoco 200 was the same as everybody else's regular and Sunoco 240 was the same as Hi-Test, and they would bring Sunoco 190 and Sunoco 260.  The 190 was suitable for use in farm tractors and lawn mowers and such, and the 260 was often used by racers.  They could dispense 190, 200, 220, 240, or 260 - for different prices, of course - and the pump would mix 190 and 260 together in the proper proportions to achieve the intermediate blends. 

Years ago, you used to be able to order pick-ups with dual fuel tanks, and there was a dashboard switch to switch between them.  I used to see forum posts by people pulling big, heavy fifth wheels with them.  They said that their trucks ran fine on regular on flat land, but would 'ping' when trying to pull the trailers over the mountains.  Their solution was to keep one tank full of regular, and one full of high test, and whenever they heard the 'pinging' they would reach over and throw the switch to the high test tank, and the pinging would go away.

Of course, that was in the days before engine computers, and I guess that's no longer necessary, anyway, I haven't heard about it in a long time.

Feeling old now . . .

Optimistic Paranoid said:

Back in what I now refer to, semi-fondly, as my Massively Misspent Youth, I used to pump gas part time while going to college.  Yes, there are separate tanks in the ground, and the tanker trucks that delivered fuel were not one big tank, they had several internal tanks................

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Yes at the gas station there are separate tanks. I said at the supply depot there is one tank and additives are then put in at the time the truck is filled for delivery.


edit: fixed formatting -ls

Now days....Ethanol is the anti-knock additive very often used to boost the octane levels up to the Premium 91 grade, ( I don't think they can add ethanol at the delivery tank )  in the old days the anti-knock additive was Lead,  then they outlawed that.

The octane boosters you buy from Walmart are probably just a lead additive.

 

I am resurrecting this topic because I have a couple of new questions but concerning the same subject.

I had a NAPA truck and RV shop install new shocks on my Adventurer 38J yesterday. It was interesting that they told me the original Bilsteins were still working just fine at age 15 years. I had them install a set of Koni shocks because they seem to be highly recommended, but they explained to me that Bilsteins are shocks and Koni's are dampeners. It was an interesting education.

While talking to the guys, I mentioned that last year, I had a problem with my CEL coming on due to a knock sensor reading, but I thought it was caused from going through the Rockies and only being able to get 85 octane gas. They adamantly told me that I should be running nothing but premium in the coach since it has an 8.1 Chevy Workhorse engine and if I don't, I'll have them tearing the engine apart to clean out all the carbon spiders. I asked if I could throw a bottle of octane booster in it when climbing the mountains and they said it would take at least a tankful to have the ECM adjust the settings and provide the proper ignition, and it would be better to simply use premium gas. They also said that the cost would be the same but paid upfront. The gas is more expensive, but I'll get more miles out of each tank. Is that true?

The previous discussion on this post indicated that lower octane gas is needed in higher altitudes. But isn't it true that you will still need a higher octane gas or an octane booster in order to get the best performance when climbing the mountains?

I'm tending to agree with the posts that said to simply buy the best gas you can afford. I live at sea level and feel that I don't need premium gas while driving in Florida but maybe getting a couple of tankfuls of premium before hitting the mountains is a good idea. I'm planning on going to the Smokies after driving through the Midwest in a couple of months if the pandemic allows, so I think I'll get premium gas when I reach western Tennessee to give the ECM time to adjust before the higher altitude.

My second question concerns a flyer I got along with the shocks from the Ultra RV Product.com. It was an advertisement for an Ultra Power performance product that will give you 56 more HP, .5-1.5 additional mpg, and 73 ft-lb or torque. Essentially, it replaces your ECM and TCM with new units. The cost is $700 plus core charges if you don't send in your units. Has anyone worked with this system and can advise for or against getting it? It sounds like it is better than the Banks system and a lot cheaper, and something that would be useful if driving through a lot of mountains, which we plan on doing for the next several years.

When we drove through the Rockies last year in both the U.S. and Canada, we didn't encounter too much difficulty while towing our Equinox. There were occasions when climbing to 10,000 feet that our speed was reduced to 22 or 23 mph. That was something we expected and I didn't push the coach too hard during those times. We simply put ourselves in the frame of mind that we weren't in a hurry and it didn't matter how long it took to get where we were going. So I'm wondering if spending $700 on this new system will be worth it to us.

I'll appreciate any advice anyone can give us if they are familiar with this system.

I could write a lot on that first question, but only have a few minutes, so I will leave it at theory is all fine and great, but in my personal experience my 8.1L likes to have at least 87 octane when driving in the mountain states that offer 85 octane as their base fuel level. As to adding octane boosters, most over the counter octane boosters do not play well with catalytic converters, so you might save vs buying higher octane at the pump now, and pay later on repairs.

As to Ultra RV Ultra Power retune vs the Banks system, they do different things, personally I would do the Banks first of the two, as it helps extract more heat from the engine. though of course the Banks system cost more.  Though by all accounts I have read the Ultra-Power retune does work as the factory tune on the 8.1L is very conservative, and the shift points are not really optimized for RV duty.

I filled my 8.1 L Vortec up with 85 in the mountains one time. Now I use mid-grade when I Mountain top (87) and regular (also 87) at lower levels.

There are many Octane boosters on the market you can add if you find you need 'em after tanking up .
Many Truck stops used to carry them (I have not looked recently will on Monday)  and all speed shops carry them since Speed Racer needs 'em.

Shocks and dampers are one and the same.  The word "dampers" is used in Europe and more correctly describes what we call "shocks." 

Carbon spiders, yeah, right.

If you think you need higher octane now, just wait till you push the engine harder with expensive modifications.