The lower number was the octane rating when at cruise in
lean condition and the higher number was the rating for a
full power rich mixture. 93 mogas would rate about 80-87,
so your 300 hp Lyc would have to be derated to prevent
detonation. The exact required changes depend on the
dash/model number and what changes can be made. You won't
get 300 hp, maybe 250-270.

The EAA has an STC for smaller engines with low compression
such as the 4 cyl. Lyc and Cont engines used on Cubs and
Champs. I don't think you could use the mogas in the big
engines without major changes to operating procedures and
maybe some hardware.


--
James H. Macklin
ATP,CFI,A&P

"Kingfish" wrote in message
oups.com...
| Back in the 1950's the airlines and military used avgas
in
| four grades, 80-87, 91-96, 100-130, and 115-145 and jet
| fuel.
|
| Jim, what do the number pairs stand for? What changes
would have to be
| made to run 93 octane mogas in my 300hp N/A Lycoming?
|