MoGas Tips, Tricks, Concerns, How To

Jay Honeck wrote:
87 octane auto gas is perfect for our low compression engines, and
certainly won't hurt them. Using "premium" (or, for that matter, 100
LL) is neither necessary nor recommended.

(Note: SOME mogas STCs do require using a higher octane car gas, but
those are the exception, not the rule.)

Don't forget, MANY planes are not considered low compression, even though
they're not exactly "high performance". For example, all the 160 hp versions
of the O-320 found in many Cherokees, Warriors, C-172s, etc, as well as the
normally aspirated 180 hp O-360 found in Cherokee 180s, REQUIRE higher octane
than 87 octane car gas. I believe, for most of them, they could get by with
less than 100, but would certainly need super unleaded as a minimum.

--- Jay


--

Jay Masino "Home is where the critters are"
http://www.JayMasino.com
http://www.OceanCityAirport.com
http://www.oc-Adolfos.com

: than 87 octane car gas. I believe, for most of them, they could get by with
: less than 100, but would certainly need super unleaded as a minimum.

True. The high-compression (8.5:1) O-360/O-540's were certificated on 91/96 avgas. The Petersen STC (the
only one applicable to high-compression engines) requires mogas with the appropriate ASTM ratings and to have an
anti-knock-index (Average of Research and Motor octane... "R+M/2") of 91 or higher. When I bought my STC, Petersen
said that even in the high-temp, altitude, CHT setup, they were unable to induce knocking or detonation even with 89.
The certificiation folks wanted a bit of safety margin.

It should also be pointed out that the R+M/2 rating does not directly compare to the avgas lean rating (i.e.
the "91" of the 91/96 or the "100" of 100/130 100LL). The avgas lean rating testing setup more closely resembles the
Motor method of the R+M/2. Typical point spread ("sensitivity" IIRC) is +-4 to 5 points on either side. In other
words, 91 AKI is more like 96 Research, 86 Motor... i.e. a bit dicey given the 91/96 rating of the aviation engine.

That said, I haven't experienced any troubles running hundreds of gallons of 93 AKI through my O-360 180hp...
summer, winter, etc.

-Cory


************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote:
That said, I haven't experienced any troubles running hundreds of gallons of 93 AKI through my O-360 180hp...
summer, winter, etc.

-Cory

I'd love to be able to, but the Petersen STC for "high" compression Cherokees is
now more than $2500, and we've got ethanol in our gas in Maryland now.

--- Jay


--

Jay Masino "Home is where the critters are"
http://www.JayMasino.com
http://www.OceanCityAirport.com
http://www.oc-Adolfos.com