Re: Ethanol vs premium

[Pete]

Back in muy young years in our outboards Dad always used regular in days of leaded fuel with no E in it. When I raced in APBA (1970’s) I used Amoco or Sunoco regular. Now I use 87 E free in the outboards, it’s available in the Orlando area. Standard Fuel station gas (87, 89, 93) have essentially the same energy available (BTU/pound), the octane difference is from the additives to get the anti-knock ratings and other stuff (some propitiatory) they put in there for cleaning, etc, so if the engine doesn’t need the higher octane premium will do nothing more than regular, but it will not hurt the engine just your wallet. Octane additives will change the burn time profile of the fuel, higher octane results in slower burn time.

See here for more detail:

http://www.factorypro.com/tech/tech_tun … power.html

If you determine the compression ratio of the service 2 cycle engines related to the top of the exhaust ports (not the full cylinder volume as used in 4 cycle engines) which is when the compression gasses are fully sealed from escape they are in the 6.5:1 range thus octane requirements are not that high and 87 will suffice. Even my race engine (Merc 25ss and Yamato) are in that range and run great on 87 E free.

Unless the old engine is properly modified for E fuel try to get the E free for no water issues in the fuel even if it’s the premium and the engine doesn’t need it.