4/20/2004 by Horizon Engineering Manager John Adams
Copyright:© 2004 Horizon Hobby, Inc.
If you read the R/C car magazines, engine instruction manuals or talk
to local racers, you'll likely find conflicting information about car
fuels. The main controversy seems to focus on how much and what type of
oil is needed for a car fuel.
Here the straight scoop based on over 15 years of experience that includes
working closely with engine manufactures, industry experts, top-level
racers and the results of testing literally hundreds of formulas in all
types of car engines and conditions.
Why Not Airplane Fuel
engines operate in a totally different environment than do airplane engines.
Airplane engines spend a great deal of their running life at full rpm,
they have a constant airflow from the prop to aid in cooling and instant
throttle response and acceleration is not as critical as with a car engine.
engines spend most of their life accelerating from one corner to the next
and are seldom at full RPM for more than a few seconds. They rely on an
oversize heat sink head to dissipate combustion heat and racers actually
tune car engines based on throttle response.
Fuel designed for airplanes typically have from 15 to 20% oil. While the
manufactures that truly understand the requirements of car engines typically
put 8 to 12% oil in their car fuel.
Why 8% to 12% Oil
Using high oil content fuels (above 15%) in gas car engines won't provide
improved engine life, as some would expect. Through extensive testing
we've discovered the point of diminishing return as far as oil content
to engine life is actually around 8% for most car engines. In other words
any more oil than 8% in the fuel does noting to improve the life of a
car engine. In fact the secondary effects of high oil content fuels can
actually cause engine damage by encouraging over lean runs. Here's how.
Using high oil content fuel causes a car engine to be unresponsive during
acceleration acting as if the engine were running rich. Typically when
using high oil content fuel, in order to get crisp acceleration and response,
an engine will need to be adjusted overly lean. In addition the high oil
content prevents lean bog when an engine is over-leaned thus allowing
the engine to run at this lean setting without the customary telltale
lean bog warning letting you know the engine is overheating.
In summary, high oil content fuels don't give added protection. The point
of diminishing return from a protection standpoint in a gas car application
is about 8% oil depending on the oil type and engine. Anymore oil than
this doesn't offer added protection and has potential secondary effects
that reduce performance and can actually cause you to over lean your engine
in an attempt to get crisp throttle response and acceleration. Do yourself
a favor and follow these two rules:
Rule #1- Always use a high quality fresh fuel designed specifically
for gas car use that has between 8% and 12% oil preferably with at least
some castor in it. (We recommend Blue Thunder Sport or Race Formula)
Rule #2 - Don't use airplane fuels or any other type of fuels that
have over 15% oil in your gas car engine.
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