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Octane and Octane Boosters
Jay,
What are your feelings about octane boosters for a lake motor that has
155lb. of compression (Mercury), or whatever is considered too high for OMC
and Yamaha to run 93 octane fuel? Do they work if you only need 100 octane
or so? Is there one you would recommend?
Thanks,
Dave R
Dave,
I just read an article in Hot Rod Magazine where they were making dyno pulls
with an octane booster additive (104+) vs. slowly boosting the octane rating
with racing gasoline. The octane booster did pick up slightly more
horsepower over pump 92 octane, but in comparing it with the higher octane
racing gasolines the octane-boosted mix was not as good. This is a 4-cycle
motor though, not a 2-cycle. Unlike the 4-cycle engine, which seemed to
increase horsepower as the octane rating increased, the 2-cycle engine will
loose horsepower when the octane rating is increased over and above the
detonation point. Of course, one would not want to go on the edge of
detonation and a cushion should be used (a bit higher octane), as the
consistency of pump gas is very bad.
Most
higher octane fuels have a slower burn rate, thus preventing detonation, but
a 2-cycle engine has a short duration time whereby the piston, which acts as
a valve, has ignition, then passes the exhaust port, and if the gases burn
too slow you can loose the “push” of the piston by the unburned charge
escaping out the port when the burn should have already been over. I read a
good article a couple of years ago where Klotz was testing their race gases
with different octanes on a 2-cycle snowmobile. The result was burned
pistons when the octane was too low, and decreased power output when the
octane was too high. One might think the more octane, the better - that is
simply not so. There is a "sweet spot " where every outboard motor is at
its peak horsepower, with the prop, hull weight (and configuration),
geographic location, etc., every motor's need is a bit different.
At 155 lb. of compression with stock timing, I would splash a little racing
gas (15 gals Super with 3 gallons of say, 110 octane) and you should be just
fine. I don't know what the octane booster costs, but if you were to run 20
or so gallons of fuel I would feel the "splash" thing would be more cost
effective. One note: I don't know what the effects of the additive to a
2-cycle motor with the introduction of 2-cycle oil via oil injection or pre
mix would do would be.
Good luck and Thanks for asking JSRE
Jay @ JSRE
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