What Gas Octane Rating For Mower ?

[wag123]

Originally Posted by 92saturnsl2
Quote
I reiterate, the low compression ratio of small air cooled engines does not require a higher octane rating than 87. If a small air cooled engine had a high enough compression ratio to require higher octane fuel, you wouldn't be able to pull start it.
Regardless, if it makes you feel better using higher octane fuel, go ahead and use it, it won't hurt anything.


This just isn't true. Compression ratio and octane are not the only attributes that determine the potential for preignition. Engine/combustion chamber design (and resulting combustion stability), ignition and valve timing, air/fuel ratio, altitude, temperature and other variables come into play. Just because an engine has a lower compression ratio does not make it invulnerable to preignition.
Yes, it IS true.
I never stated that an engine having a low compression ratio is invulnerable to pre-ignition. The use of higher octane gas in-and-of-itself does not necessarily eliminate pre-ignition.
It is a FACT (not my opinion) that small air cooled OPE engines have a low compression ratio, and it is a FACT (not my opinion) that unsophisticated and relatively crude air cooled OPE engines, especially lawnmower engines (which is what the OP inquired about), do not require the use of gas with over 87 octane. Only a very small number of high performance chainsaws actually need higher octane fuel.
I am trying to educate you guys with the knowledge I have gained working in the OPE industry over many years. You can disagree with me if you want, it is up to each of you to decide whether or not I am blowing smoke, I can assure you that I am not. After disassembling literally thousands of lawnmower engines (and other small OPE engines), I never saw one that was damaged by the use of 87 octane fuel. Furthermore, I have never witnessed the improved performance of any lawnmower using higher octane gas (other than the use of E0).

 

[Srt20]

I understand this is BITOG, and most members here way over analyze. But the amount of bad advice, myths, and flat out just wrong information in this thread is astounding.

If you don't know what is what, which most on this thread dont, just follow the owners manual. If it says use only 91 or no ethanol, then use it. If not use whatever the heck you want. The only person you're hurting is you and your wallet.

The guys that are correct or at least mostly correct, stop trolling the guys that think they know better. You're not going to change their minds.

 

[92saturnsl2]

Quote
I reiterate, the low compression ratio of small air cooled engines does not require a higher octane rating than 87. If a small air cooled engine had a high enough compression ratio to require higher octane fuel, you wouldn't be able to pull start it.


Again, an engine can require higher octane WITHOUT being high compression (whatever that is), or in your words, compression so high you can't pull it. There are dozens of variables. You keep mentioning compression ratio like it's the only factor that might influence the octane requirement and that's just baloney.

There ARE small OPE engines that require 89 octane and it has nothing to do with compression. I get what you're trying to say- In a nutshell, 99.9% of OPE manufacturers design engines for 87 octane, so using higher than that is wasting your money. I agree with that sentiment, but it's not because they are air cooled, low compression engines. The reason nearly all OPE engines will run fine on 87 octane and see no improvement going beyond that is because that's what they were designed for, because the engineers know that consumers (the vast majority) are going to put regular 87 octane in these engines. So timing, fuel mixture, rod/stroke ratio, all sorts of variables are dialed in such that you get maximum efficiency, low emissions and power output out of 87 octane fuel, or whatever the manual is suggesting. To say that just because it's a low compression unsophisticated (which is not true btw) air cooled engine, it will take 87 octane is wrong.

 

[odie]

Unknown 90 non E for mowers and snowblowers for about 10 years .

 

[Silverado12]

FWIW my dealer told me to run at least 89 octane but I run premium most of the time. Sometimes I fill up with 87 if that's all I have and haven't honestly noticed a difference. There seems to be truth to stored gas losing octane.

 

[dinofish]

Originally Posted by kschachn
Originally Posted by dinofish
If it makes you 'feel' that it is all my 'feelings', then go right ahead. You are more than welcome to your 'opinion' vs my direct observation. If it is something else giving better starting with high octane, then address it.

But you can prove it to yourself. Buy two cans and try it with two different fuel types on a small engine after having them both sit for a month. Then you can tell me how you 'feel' about the results. Remember that you have to test it in a small engine. Like a 4-cycle leaf blower, or trimmer, etc. The effects are more immediate and noticeable in smaller the engine.

Again, you don't understand what you're saying. There are multiple of ways a blender or refinery can create an apparent octane rating for a fuel and it is these differences in composition you are observing. It is not the octane number itself.

Well, I don't know what exactly is causing it, whether it is octane or something else. But I definitely notice a difference in premium vs. regular in smaller engines when cold starting.

 

[2K2AcuraTL]

I use 91 octane R+M/2... for the simple reason that 2 of 3 cars i service burn premium..
therefore when I need gaz for OPE, lawn tractors, generators etc...the gerry-can gets filled when I fill up on my Acura's.

but ..when i bought my Stihl weed-trimmer some years ago...i distinctively remember the one comment the tech left me with.... " burn premium gaz in this .... and ALL your other small engines..."
I suspect thats just because he was trying to get me to use E0 fuel. as -most- fuel suppliers deliver E0 in 91 in my neck of the woods.

This wasnt the case when the main ppl movers in the house [all GM] used 87... OPE got 87.. snowblower had surging issues...a weed-eater went in the garbage [ hence the Stihl..] ... and.... i'll stop here.
I have no concrete evidence that 87 E10 was was the main issue... things that make you go Hmmmmmm..
Then My father-in-law had issues with an outboard and a chain saw.. woudlnt start.. etc... told him to use 91 because of E10 in 87... yes.. he had to replace fuel lines and a few other maintenance.. things got back to normal..
ok its all subjective...
yes you can make your own E0 87 with the -add water to gas- shake and drain the water trick... then its not 87 anymore, because the E elevated the octane level from the start..

91 works for me .. a lot less hassle.. and proven performance in my garage.
my 2c .. for what its worth.
J.
Stay safe...

 

[jeepman3071]

Originally Posted by 2K2AcuraTL
I use 91 octane R+M/2... for the simple reason that 2 of 3 cars i service burn premium..
therefore when I need gaz for OPE, lawn tractors, generators etc...the gerry-can gets filled when I fill up on my Acura's.

but ..when i bought my Stihl weed-trimmer some years ago...i distinctively remember the one comment the tech left me with.... " burn premium gaz in this .... and ALL your other small engines..."
I suspect thats just because he was trying to get me to use E0 fuel. as -most- fuel suppliers deliver E0 in 91 in my neck of the woods.

This wasnt the case when the main ppl movers in the house [all GM] used 87... OPE got 87.. snowblower had surging issues...a weed-eater went in the garbage [ hence the Stihl..] ... and.... i'll stop here.
I have no concrete evidence that 87 E10 was was the main issue... things that make you go Hmmmmmm..
Then My father-in-law had issues with an outboard and a chain saw.. woudlnt start.. etc... told him to use 91 because of E10 in 87... yes.. he had to replace fuel lines and a few other maintenance.. things got back to normal..
ok its all subjective...
yes you can make your own E0 87 with the -add water to gas- shake and drain the water trick... then its not 87 anymore, because the E elevated the octane level from the start..

91 works for me .. a lot less hassle.. and proven performance in my garage.
my 2c .. for what its worth.
J.
Stay safe...










That is likely why. In my area, ALL grades of fuel have ethanol in them, so using anything other than 87 would just be a waste of money. If you can find E0 fuel then that's awesome, and continue to use it if you can get it. Unfortunately a lot of my customers have just been told "use premium fuel it's better" and then they come to me with equipment that won't start swearing they used nothing but 93.


What many in this thread are leaving out is that 93 is only the octane rating meaning it's purpose is being able to withstand higher compression before igniting than 87. Most small engines have very low compression and don't run hot enough to have detonation issues. 93 isn't necessarily a "better" or "cleaner" fuel than 87. Unless the owner's manual recommends using something higher than 87, you are just throwing money away. Just because they are air cooled, does not mean they run crazy hot cylinder temps.

 

[dinofish]

Originally Posted by jeepman3071


That is likely why. In my area, ALL grades of fuel have ethanol in them, so using anything other than 87 would just be a waste of money. If you can find E0 fuel then that's awesome, and continue to use it if you can get it. Unfortunately a lot of my customers have just been told "use premium fuel it's better" and then they come to me with equipment that won't start swearing they used nothing but 93.


But what about oil? Did they change the oil? Run it low? Use the right type?

 

[92saturnsl2]

I've never seen 91/93 octane non-ethanol fuel, doesn't make much sense. Ethanol contributes to higher octane, so to provide a premium fuel with no ethanol requires another formulation of gasoline with an even higher starting octane.

Whereas to create an 87 ethanol-free octane, one might use some percentage of the more premium grades (mid or higher), drop the ethanol and you're back to 87.

 

[Astro14]

Originally Posted by 92saturnsl2
I've never seen 91/93 octane non-ethanol fuel, doesn't make much sense. Ethanol contributes to higher octane, so to provide a premium fuel with no ethanol requires another formulation of gasoline with an even higher starting octane.

Whereas to create an 87 ethanol-free octane, one might use some percentage of the more premium grades (mid or higher), drop the ethanol and you're back to 87.


Lots of different additives can be used to create 91/93 non ethanol fuel. None of them are as cheap as ethanol. But they used to be commonplace.

Same "starting octane" as e10.

 

[jeepman3071]

Originally Posted by dinofish
Originally Posted by jeepman3071


That is likely why. In my area, ALL grades of fuel have ethanol in them, so using anything other than 87 would just be a waste of money. If you can find E0 fuel then that's awesome, and continue to use it if you can get it. Unfortunately a lot of my customers have just been told "use premium fuel it's better" and then they come to me with equipment that won't start swearing they used nothing but 93.


But what about oil? Did they change the oil? Run it low? Use the right type?



It's a mixed bag. Some are very good about oil, they usually have older well taken care of machines in for repairs or service. Others clearly don't even know it requires oil.

 

[Woody71]

Per my owner's manuals, I use 87 in my mower and 91 in my 2 cycle engines.

 

[Surestick]

The Tecumseh flathead engine in my push mower has no issues with campstove Naptha being used in it, even cutting heavy wet grass, and that has a RON of 70 or so according to a quick google search.

I imagine OHV engines with a bit more compression might have more of an issue with that.

 

[Slick17601]

I run Wawa 89 E0 in my small engines.

 

[rokwldr]

I use REC90 in all my power equipment including my outboard and have never had fuel issues. I have in the past used 97 with 10% ethanol and had issues and burned up a weed eater engine. Got a new one and went to Rec90 and have not had an issue. Some places here there is 87 unleaded but not near me.

 

[nomas]

There are always going to be those guys that think higher Octane = more power .

 

[tundraotto]

Originally Posted by nomas
There are always going to be those guys that think higher Octane = more power .


this is true - more octane only means more power if your engine has a system that can advance the timing to take advantage of it. On an OPE engine - with ~8:1 compression ratio, no gonna happen.

 

[RyanY]

Lots of debate on which gas to use or not to use in OPE, but I find it easiest to just follow the owner's manual (pic below is from my 1978 B&S 3 HP). I use 87 E10 and run it dry at the end of the season, as suggested. If I could find 77 octane I would run it.

 

[RDY4WAR]

I've also used 87 E10 in all of my lawn equipment for several years and haven't had an issue.