Way OT: Sales guy tells me to NOT run premo gas in small engine?

[GregSY]

My old Ford F-250 V10 would get 14MPG highway when it was unloaded. I checked that numerous times on road trips. When they introduced ethanol, it dropped to 12.5MPG.

Ethanol is yet another example of government interference and for all the wrong reasons.

 

[Laverda]

Should run what it's designed for. Lower octane rated fuel has more energy. Higher octane starts to burn in a narrower temperature band, that's why you need it with higher compression. At higher compressions you don't want it kicking off too soon, preignition destroys pistons.

I can't think of how higher octane fuel would hurt an engine, but could be possible. But running hi-test in an engine that doesn't need it is definitely a waste of money and you'll get less work out of it.

What are you talking about? Lower octane fuel does not have more energy. This is complete BS. You will find many more people who believe that high octane fuel actually has more energy which is also BS. You also mention higher octane fuel could possible hurt an engine, please explain how?

Then you mention pre-ignition as related to octane, which is also BS, pre-ignition is caused by hot sports in the combustion chamber, not the fuel octane. A fuel which is too low an octane for a specific engine will cause knocking, not pre-ignition!

I agree completely about aviation fuel, it can sit for many years and will not absorb moisture or deteriorate. If you can afford it, a very good choice.


Emanuel Goldstein, it appears you don't know that per-ignition and knocking are not the same thing. And again, the octane of gasoline, has nothing to do with the energy (BTU's) in the gas or pre-ignition. Higher octane fuel is designed to prevent detonation (knocking), not pre-ignition. Pre-ignition means the gasoline has ignited before the spark plug has fired, which is a really bad thing. Knocking means the combustion chamber pressure and temperature has reached a point that the fuel instead of burning has detonated which causes the knocking noise you hear.

 

[EmGo]

What are you talking about? Lower octane fuel does not have more energy. This is complete BS.

Regular has more volatile hydrocarbons than ethyl, that's why it ignites easier, has a faster flame front, is more prone to knocking, and has a higher btu content.

Pre-ignition and detonation are the same thing, the fuel lighting off before it should, there haven't been "hot spots" in the combustion chamber for fifty years. That's a meaningless distinction.

I was going to go into this more, but since you don't know shit and it involves a lot of typing, I'm not going to bother. It's not worth it.

But I'm going to believe Mert and Mike Libby and CR Axtell over you.

 

[johansen]

The difference in thermal energy per kilogram of 87 vs 92 octane gas is negligible compared to the difference from one supplier to another with regard to the amount of ethanol in it (which most people know has a good bit less kj/kg) (contains up to 10% ethanol) well some states are up to 15%.

Doesnt take much iso octane or other additives to turn 87octane into 92. Yes the additives are heavier molecules that burn slower.

But if those heavier molecules have more carbon then it offsets the difference. Diesel is 38kilowatt hours per gallon compared to 33 for gasoline.

In winter they dissolve more butane and propane in the gas which is one of the reasons you get worse gas milage in winter (the bigger reason is the colder air is more dense) and everything else including your tires have more friction.

 

[EmGo]

The difference in thermal energy per kilogram of 87 vs 92 octane gas is negligible compared to the difference from one supplier to another ...

I don't doubt you. The only reason I'd point out that lower octane fuel theoretically has more power is, a lot of people are convinced of the opposite. And that isn't true. Higher octane does not give more power. Higher compression does.

 

[eKretz]

Regular has more volatile hydrocarbons than ethyl, that's why it ignites easier, has a faster flame front, is more prone to knocking, and has a higher btu content.

Pre-ignition and detonation are the same thing, the fuel lighting off before it should, there haven't been "hot spots" in the combustion chamber for fifty years. That's a meaningless distinction.

I was going to go into this more, but since you don't know shit and it involves a lot of typing, I'm not going to bother. It's not worth it.

But I'm going to believe Mert and Mike Libby and CR Axtell over you.

I agree with most of this. Pre-ignition is fuel igniting before the spark plug is fired, which is the same thing as detonation, and is the same thing that causes the "knocking" noise (or marbles clicking together, if you will) in an engine. That can cause hotspots and melted parts in an an engine all by itself.

Low octane gas is more volatile than high octane gas, that's all. It ignites easier. That doesn't necessarily mean it releases more energy when it combusts. It may or it may not depending on lots of other factors and the exact formulation of the fuel.

A bigger factor is the car and its fuel injection system. Many cars today can advance the timing and find the sweet spot in terms of ignition timing where they make the most power right on the edge of detonation. Higher octane gas means the timing can be advanced further without detonation occurring, making more power.

 

[john.k]

Any electronic ignition car engine has a "knock detector" and runs the ignition advanced just short of pre ignition......this is one of the reasons for variance in fuel milage with different fuel octane......As mentioned ,the difference between ethanol and hydrocarbon in energy content is quite large,and here accounts for about 4 cents a litre less energy value in a 10% E fuel.

 

[john.k]

IMHO,there are two kinds of knock.....preignition is a heavy knock ,quite destructive to pistons etc.....there is another kind of knock which is less harmful,and that is knocking of the unburned end gasses in the cylinder ....more common in flatheads than modern OHVs.

 

[triumph406]

Low octane gas is more volatile than high octane gas, that's all. It ignites easier. That doesn't necessarily mean it releases more energy when it combusts. It may or it may not depending on lots of other factors and the exact formulation of the fuel.

Not sure about that, used to crew for a Baja Bug in the 1000, last year I went they changed the heads to run on whatever s*** fuel was avilible south of the border. The other reason was safety as the 105 octane the bug originally ran on was very volatile.

Somebody with a lot of experience showed us how volatile 105 octane was, cup of fuel on the ground and a match, went off way faster than regular gasoline. After that we were very careful refueling the Bug.

 

[eKretz]

Not sure about that, used to crew for a Baja Bug in the 1000, last year I went they changed the heads to run on whatever s*** fuel was avilible south of the border. The other reason was safety as the 105 octane the bug originally ran on was very volatile.

Somebody with a lot of experience showed us how volatile 105 octane was, cup of fuel on the ground and a match, went off way faster than regular gasoline. After that we were very careful refueling the Bug.

That 105 probably had other goodies in it too (race fuel?)...it wasn't just the octane causing that. And anyway, regular gasoline goes up pretty damn fast if you spill a cup full on the ground and toss a match in it. Not sure the difference would be easily discernible without a direct comparison and maybe a high speed camera.

 

[BoxcarPete]

OK, looks like we are due for a purely pedantic post, so here goes:

Volatility and ignition temperature are technically separate things. Volatility is related to the vapor pressure of the fluid, and determines how readily it will move from liquid to gaseous state. Ignition temperature is exactly what it sounds like, the temperature that the fuel/air mix needs to reach to spontaneously form a combustion reaction.

The octane rating is a number assigned to the fuel based on performance in a test engine on what compression ratio triggers autoignition compared to a mixture of iso-octane and n-heptane. It has nothing to do with the energy of the fuel. E-85 is well known to be higher octane than premium gas, but as we also know, ethanol is lower energy than a pure hydrocarbon fuel.

 

[SteelrFn]

So talking to a mfgr of a piece of outdoor power equipment.............has commercial Kohler engine. Says they have customers with engine issues. He tells me the common denominator is because they are runnin' premium instead of 87 octane???? HUH??? Tells 'em to run 87 and stabil.................huh? Every single small engine guy I have ever talked to recommends 91 octane...............am I missing something? Sales guy sends me this article.......................?????? I think a vehicle and a small engine might be a bit different.......................

If My Car Recommends Regular Gas, Is It Good to Use Premium Occasionally? | News | Cars.com

I run non ethanol in all of my small engines. I was told by a guy that fixes small engines for a living that the ethanol will eventually eat through your carburetor seals and most of them are built in now so you can just replace the seals, you have to replace the entire carburetor. there are only about 300 gas stations in PA that sell non ethanol and I am fortunate to live close to one.

 

[ifixcnc]

In western PA most of the Country Fair stations have No Eth.

 

[eKretz]

OK, looks like we are due for a purely pedantic post, so here goes:

Volatility and ignition temperature are technically separate things. Volatility is related to the vapor pressure of the fluid, and determines how readily it will move from liquid to gaseous state. Ignition temperature is exactly what it sounds like, the temperature that the fuel/air mix needs to reach to spontaneously form a combustion reaction.

The octane rating is a number assigned to the fuel based on performance in a test engine on what compression ratio triggers autoignition compared to a mixture of iso-octane and n-heptane. It has nothing to do with the energy of the fuel. E-85 is well known to be higher octane than premium gas, but as we also know, ethanol is lower energy than a pure hydrocarbon fuel.

Yes that's true. I was using volatile as a "prone to rapid or explosive change" term, which is sort of a borrowing/incorrect use, but you are technically correct. Somebody write this down: 2 pedant points for Pete!

 

[Terry Keeley]

Kretz is right on, he's full of shit.

"In Canada, Shell V-Power Nitro+ premium gasoline does not contain ethanol." This is the only gas I run in my Golf R and small engines, it's up to C$1.75/litre now in T.O. (about US$5.35/US gal.)

 

[Bill D]

Off the top of my head premium gas burns cooler, is harder to get started, and will form more soot in the cylinder and exhaust.
Bill D

 

[Scottl]

the octane no. is just the antiknock rating. The higher the compression (esp. on turbos), the higher the octane needed to help prevent detonation. Cars have had knock sensors and the like for decades, so you can run lower octane fuel in high compression engines at a lower power output. Usually the only downside to running higher octane fuel than needed is the cost. I can't imagine relatively low compression small engines like you'd find in outdoor equipment would need anything higher than 87 octane, though I can't see why that would hurt them if you did.

I've been running 93 octane in all my small engines for many years.

Why? Because some of my 2-cycles require it (per manufacturer) and I don't want to keep multiple grades on hand and risk grabbing the low octane by mistake.

I pre-load the large gas can with storage dose of Stabil before going to the gas station and then mix the 2-cycle blend one gallon at a time. I use the storage ration of Stabil as a precaution in case something happens (as it often does in life) and something gets put away without the normal storage preps. Am I wasting money? Yes but it's a tiny amount in the household budget. Spoiled produce wastes far more.

Never had problems using the higher octane fuel in run of the mill mowers and other 4-cycle equipment. The Stabil also helps with the ethanol, which runs up to 10% here. Oh, and I'm a fanatic on oil changes and other maintenance.

 

[Scottl]

Off the top of my head premium gas burns cooler, is harder to get started, and will form more soot in the cylinder and exhaust.
Bill D

Tuning can largely compensate for both and periodic fuel additives keep things clean.

As for hard starting, that mostly happens if the wrong season blend is used. I dispose of the excess in one of the vehicles and buy fresh as the seasons change.

 

[Scottl]

I agree with most of this. Pre-ignition is fuel igniting before the spark plug is fired, which is the same thing as detonation, and is the same thing that causes the "knocking" noise (or marbles clicking together, if you will) in an engine. That can cause hotspots and melted parts in an an engine all by itself.

Low octane gas is more volatile than high octane gas, that's all. It ignites easier. That doesn't necessarily mean it releases more energy when it combusts. It may or it may not depending on lots of other factors and the exact formulation of the fuel.

A bigger factor is the car and its fuel injection system. Many cars today can advance the timing and find the sweet spot in terms of ignition timing where they make the most power right on the edge of detonation. Higher octane gas means the timing can be advanced further without detonation occurring, making more power.

Years ago GM had a recall on the supercharged models. People were ignoring the manual and running lower octane gas which made the timing retard and the exhaust hotter. Coupled with leaking rocker covers there were enough engine fires to warrant the recall. AFAIK none of those running the proper octane had engine fires.

 

[Doozer]

Lower octane fuel is easier to light off with a weaker ignition system.
Likely the reason it is recommended for small engines.
You guys really complicate things.

----Doozer