85 octane question

[Travelin' Texans]

And if it happens to be available at the pump DO NOT confuse 85 octane with E85, THEY ARE NOT the same fuel. If your vehicle is not rated for Flex Fuel it's not designed for E85. Also even if you can use the E85 it may be several cents cheaper but the mpg will also suffer so it actually may cost more in the long run. Ethanol blended fuels up to 10% will lower your mpg about 10% so it's only real benefit is not lowering the use of fossil fuels but rather providing a market for corn.

[MJC62]

As has been stated if you remain above 4000 feet you can use 85 octane. However, the owner's manuals of my Ford and my Jeep specifically state 87 octane or higher. I still gas up with 87. The peace of mind I get knowing I am following the mfgrs recommendations easily offsets the extra few bucks it costs to fill either vehicle

[Bill Johnson]

Originally Posted by Scubawise

Thx saw this
Your engine is designed to run on 87 octane at sea level. It will run just fine at 4000 ft and above on 85 octane. With lower air pressure comes lower combustion chamber pressure and reduced chance of ping. Don't waste your money on octane you don't need.Jan 28, 2018

Engine masters tv show took an engine and ran it on 87 to 110 octane on the dyno and it didn't matter what octane rating they used the horsepower and torque were the same it didn't matter as long as it doesn't knock. They tried E85 and that did increase horsepower because alcohol increases the oxygen going in the engine

[ducksface]

I think we need to see some real, not uncle brothers cousin in 1971, conclusive proof of 2 octane difference being anything but
2 octane difference
In our industrial barge commercial type engine.

Show us some damage.
Let's start with a 300,000 mile engine and work back to rv type miles.

[Chateau_Nomad]

So
You're claiming
2 octane lower
making a difference
is alternative facts?

There's your dinner...

[ducksface]

Originally Posted by Chateau_Nomad

So
You're claiming
2 octane lower
making a difference
is alternative facts?

There's your dinner...

Negligible, not alternative.
No real world consequence.

[Bob Denman]

https://www.thorforums.com/forums/at...1&d=1637775860

[Bob Nodine]

Scubawise are you confused yet? Funny how when someone ask a question the thread always spirals into an abyss of controversy. Remember what Joe Friday always said, "just the facts ma'am".

I forgot that some of you might be young whipper snappers and not know who Joe Friday is. Look up Dragnet.

[dkoldman]

Originally Posted by Chateau_Nomad

So
You're claiming
2 octane lower
making a difference
is alternative facts?

There's your dinner...

Originally Posted by ducksface

Negligible, not alternative.
No real world consequence.

Isn't this akin to oil filter reviews, analysis and the science, or call if alternative facts if you will.

Anybody can laugh at me, make fun and call me names, but I use Fram oil filters. When a Fram oil filter takes I out one of my engines after about about 150 years of engine use in various automobiles for myself and the family, then maybe, just maybe I may think the type of cardboard used inside an oil filter make an appreciable difference. Besides in 4 to 8 months the filter is gone for a new one.

[dkoldman]

Originally Posted by MJC62

As has been stated if you remain above 4000 feet you can use 85 octane. However, the owner's manuals of my Ford and my Jeep specifically state 87 octane or higher. I still gas up with 87. The peace of mind I get knowing I am following the mfgrs recommendations easily offsets the extra few bucks it costs to fill either vehicle

I actually thought my manual for F-53 says to use 87 octane and not anything higher? Maybe I am confusing vehicles, but I am fairly certain that it is not a good thing for all vehicles to use a higher octane than recommended. But I do follow your premise. But for me; if 87 is not available, I will get 86 or 85 which ever is cheaper. I don't think about anything other than if the gas costs more than $3 a gallon, then I start to get pissed It is down to $2.88 here for 87 octane; so I may be removing my For Sale sign soon. If I can afford the gas, I can afford the RV again

[Bob Nodine]

Originally Posted by dkoldman

I actually thought my manual for F-53 says to use 87 octane and not anything higher? Maybe I am confusing vehicles, but I am fairly certain that it is not a good thing for all vehicles to use a higher octane than recommended. But I do follow your premise. But for me; if 87 is not available, I will get 86 or 85 which ever is cheaper. I don't think about anything other than if the gas costs more than $3 a gallon, then I start to get pissed It is down to $2.88 here for 87 octane; so I may be removing my For Sale sign soon. If I can afford the gas, I can afford the RV again

Not sure how valid this is but my Dad always told me that you need the higher octane on high compression engines to keep them from pinging. If the compression is to low for the high octane fuel then there is a danger it will still be burning when the valves open and could burn the valves.

[dkoldman]

Originally Posted by Beau388

Yes if you are consistently above 4,00 ft above sea level. Should you descend below that elevation, you should use 87 octane gasoline. It works about the same as the cold air pressure in your tires. As you go up in elevation the outside air pressure decreases so the air pressure in your tires will increase. The reverse is true when you descend in elevation.
Most modern gasoline engines have knock sensors to prevent damage if fueled with a lower octane fuel than is recommended. The Ford V-10 does not use knock sensors, so it up to the owner to use the proper fuel.

I am glad you posted this as now I can say, I follow the Science and the Math

This is not Rocket Fuel and we are not Rocket Scientist (well not all of us any way, there are some nuclear folks around ) But anyhoo...

What you say is the same for me by default, when I need gas, I pull into a gas station that has the lowest advertised price from a readable sign 1 /2 mile away.

When I get there and I don't see 87 octane, I say hey, I must be at higher altitude or lost. I find the cheapest gas possible which is usually the 85 and I fill up. I drive where I got to go until I get down to 1/4 tank again and repeat. So in a way, I could say I use 85 octane all the time; but since I live in Dallas/Ft Worth or similar 85/86 is not available; so the cheapest I can get is 87 octane

Your science simply confirms why it may or may not be available.

[dkoldman]

Originally Posted by Bob Nodine

Not sure how valid this is but my Dad always told me that you need the higher octane on high compression engines to keep them from pinging. If the compression is to low for the high octane fuel then there is a danger it will still be burning when the valves open and could burn the valves.

From FTC ( in the event you find them credible)

In a consumer notice, the Federal Trade Commission, notes:

“In most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner.” Jan 11, 2020

[dkoldman]

Originally Posted by Bob Denman

Haven't we had enough of "ignoring the science"?

Originally Posted by Scubawise

Oh no stop. Stop montana is excellent..go camping..even KOA has bears ..just call our bear holiness. They will send an F15. JOKING

I was just trying a little sense of humor to bring us all back together again. If anyone says or disagrees, or find any type of link, or even reference the word agenda on why you shouldn't use 85 octane gas given it is there and 87 is not available; my head is going to explode; and I am out of Duck Tape

@Scuba,
I was in Banff Canada during mating seasons and Moose are allowed to freely roam the streets, you can touch them. One was standing in the front of a door to a bar we were trying to get into. I had to wait and 20 minutes because I wasn't as bold as the natives

Inside the bar, there must have been about 20 people. after about 2 hours, I had been told "that during the mating season, the male moose can only see two things, and trust me, you don't want to be either one " about 100 times

You make Montana intriguing, I love camping; but I have watched most all of the Grizzly movies; so I am not to keen being in real woods with real Grizzlies; especially now knowing the State is putting Grizzlies back in woods were campsites are, or may be I have heard of catch and release fish, squirrels and even deer, but Grizzlies? I don't think so

[Bob Denman]

Soooooo... You're admitting that you DO have an agenda also?!?
JK: Bro'. Have a Fan-Dang-TASTIC Thanksgiving!

[dkoldman]

Originally Posted by Bob Denman

Soooooo... You're admitting that you DO have an agenda also?!?
JK: Bro'. Have a Fan-Dang-TASTIC Thanksgiving!

Ah man, you got me, but you will never catch me.

[ducksface]

I might have the ultimate
Octane disparity
Story

60 year old three two- barrel car. 60 year old carbs. Three carbs, only one has a choke.
Spent its life at 500 ft altitude using 100 octane leaded aviation gas(owned by a crop duster)
Recently came to live at 7,000 ft altitude and 91 octane pump gas.

That's a nine point spread and lab vs real octane numbers.

It hasn't missed a beat and does not detonate.(I dont know why other than they had it tuned wrong but it fits where it is now.)

Truthfully I thought it would require major work just to start.

[16ACE27]

Originally Posted by Beau388

True the air is less dense, but your engine has a one bar Manifold Air Pressure (MAP) sensor and an Initial Air Temperature (IAT) sensor that allows the Engine Computer Unit (ECU) accurately determine the actual air density and inject the correct amount of fuel for the computed density. The feedback from the three O2 sensors ensures the fuel air ratio is correct. The reason that 85 octane rated fuel is available is the air density effectively lowers the compression ratio sufficiently to allow the engine to run successfully at altitudes 4,000 ft ASL.

The ratio remains the same.
A compression tester will show the same compressed psig (Pounds Per Square Inch Gauge)
However the psia (Pounds per Square Inch Absolute) will be lower.

The reason 85 octane is OK above 4000 ft ASL is due to the lower partial pressure of Oxygen at that altitude resulting in a less vigorous explosion when ignited. The same reason athletes have trouble competing at altitude - a deficiency of Oxygen in the mixture. Although an ECM may use an air density sensor to help calculate the optimum quantity of fuel to use in the mixture, it can not control the physics that controls the burn reaction.

[dkoldman]

Originally Posted by 16ACE27

The ratio remains the same.
A compression tester will show the same compressed psig (Pounds Per Square Inch Gauge)
However the psia (Pounds per Square Inch Absolute) will be lower.

The reason 85 octane is OK above 4000 ft ASL is due to the lower partial pressure of Oxygen at that altitude resulting in a less vigorous explosion when ignited. The same reason athletes have trouble competing at altitude - a deficiency of Oxygen in the mixture. Although an ECM may use an air density sensor to help calculate the optimum quantity of fuel to use in the mixture, it can not control the physics that controls the burn reaction.

Maybe this is some rocket science stuff.

So if I get this right, whether my RV has an ECM or not controlling air density, if I am in a location that sells 85 octane, I should buy it because it will result in less vigorous explosions when ignited and be cheaper?

Works for me

My takeaway....
When gas prices soar, consider a vacation in the mountains and you can still afford your RV

[kwplot34]

Originally Posted by Bill Johnson

Engine masters tv show took an engine and ran it on 87 to 110 octane on the dyno and it didn't matter what octane rating they used the horsepower and torque were the same it didn't matter as long as it doesn't knock. They tried E85 and that did increase horsepower because alcohol increases the oxygen going in the engine

That was a GM 6.2L the same engine I have in my truck which has warnings on the fuel door, owners manual and a sticker on the dash when new to use 93 octane, I use 91 it's easier to find and works fine with no issues. You could run 87 in it but you better drive it like a grandma and don't haul or tow because you will damage the engine.
The reason on Engine Masters they were able to get away with it, is because the engine is in a controlled environment, they have cool air, able to keep the the coolant and oil temps down, but if you remember from watching they also said even though the engine ran on it and made good numbers DO NOT run 87 in your vehicle it will not last long, the engine is an 11.5.1 compression ratio.
They did test C16 after the 110 with no difference in performance, the test showed that no mater the octane level the fuel did it's job, in a controlled environment.