89 E10 vs 92 ethanol free in small engine

[Malador]

A local Subaru Robin mechanic told me that the manufacture recommends 89 octane fuel to slow carbon build up on the head.(i couldn't find it in the manual though)

So my choice's are running 92 without ethanol, or 89 with 10% ethanol. Does anyone have any thoughts on the matter

 

[Johnny]

92 without ethanol.

 

[bluestream]

Originally Posted By: Johnny
92 without ethanol.

X2..

I have found carbon to be a non-issue since leaded gas has gone away

 

[JHZR2]

My echo OM states 89...

 

[Malador]

Yep, I've been using the 92 in echo chain saw and weed eater because my manual says the same thing.

 

[Jakegday]

92 without.

 

[exranger06]

Is THAT why Echo always says to use 89 octane in their equipment? I have an Echo trimmer and leaf blower and always wondered why they spec'ed 89 octane. All gas around here has ethanol, even premium, so I use 89 for the Echos and 87 in everything else.

 

[Malador]

I don't think ethanol is the reason. I've owned echo's before oregon mandated the e10, and even the older one say 89.

 

[KeithS_NW_Ohio]

x3

 

[TurboLuver]

92 without..I was having fits with all my OPE using our 10% ethanol blend this year until I started using sta-bil ethanol treatment.

 

[97prizm]

I think the 89 recommendation is due to the high compression air cooled engine. You wouldn't put 85 or 87 in a acura integra race motor that has a 13:1 compression ratio.

 

[660mag]

Originally Posted By: 97prizm
I think the 89 recommendation is due to the high compression air cooled engine. You wouldn't put 85 or 87 in a acura integra race motor that has a 13:1 compression ratio.

+1
The reason for 89 vs 87 is to reduce pre-ignition.

 

[tmorris1]

Originally Posted By: 97prizm
I think the 89 recommendation is due to the high compression air cooled engine. You wouldn't put 85 or 87 in a acura integra race motor that has a 13:1 compression ratio.

A Robin engine only has like a 9:1 compression ratio so I don't think I would consider that a high compression race engine.
A higher octane fuel would reduce pre-ignition, but I doubt it has anything to do with carbon build-up.

 

[660mag]

When it comes to an air cooled engine the min octane requirement to prevent pre ignition is based on three things. Compression, timing, and combustion chamber temperature.

Intake air Temperature is hotter than other engine designs, and the timing is advanced more to maximize performance. Add compression to the formula and you get the minimum octane.

Even if the parameters of these engines do not require the highest number avi. there are still benefits to starting out higher than needed.

In a vented fuel system alcohol evaps quickly causing a more rapid drop in the fuel octane. After 2 months of storage your 93 customers octane will still be in range, while the 87 or whatever customers may not.

 

[tmorris1]

Originally Posted By: 660mag

In a vented fuel system alcohol evaps quickly causing a more rapid drop in the fuel octane. After 2 months of storage your 93 customers octane will still be in range, while the 87 or whatever customers may not.

It will also draw moisture to the fuel causing it to go bad.

 

[660mag]

Originally Posted By: tmorris1
Originally Posted By: 660mag

In a vented fuel system alcohol evaps quickly causing a more rapid drop in the fuel octane. After 2 months of storage your 93 customers octane will still be in range, while the 87 or whatever customers may not.

It will also draw moisture to the fuel causing it to go bad.

Also true.
For every ounce of alcohol that evaporates one ounce of water is added to the fuel mix.