Recently Consumer Reports published a piece how
premium grade gasoline may not be needed for vehicles due to manufacturer
recommendation versus a requirement. The article has several flaws and omits
some key factors. One aspect is the testing used two vehicles that had
recommendations for premium grade gasoline but not a requirement. The recommendations
are usually only for performance, but the testing was lacking in a variety of
situations.
It was suggested that if the feel and the sound of the engine
indicates knocking, it’s a good idea to use gas with higher octane. Feel and
sound are not good indicators of knocking or pinging. It is more serious when
it is audible but using the human ear as a guide is deeply flawed. A data
logger for the knock sensor and reading how the engine fuel mixture reacts is
the only way to determine if the octane is causing knock. Knock is detrimental,
audible knock is very bad.
Consumer Reports claimed the power difference using premium
versus regular grade gas was measured with a zero to sixty mile per hour timed
acceleration test. A 0-60mph time is a
very poor comparison of horsepower. It is too launch dependent and only runs
through the first two gears typically. A more powerful car may have a more difficult and therefore slower
launch due to managing traction. This confounds the data even though it makes
up the time once rolling. There
are two reliable ways to measure horsepower without removing the engine; a
chassis dynamometer and full throttle acceleration from a roll at a given speed
and gear selected. The testers cannot feel a few more or less horsepower
either. Not many people are able to accurately.
The article never mentioned mid-grade fuel nor the
premium octane rating ranges. 91 octane is prevalent in California but 92 and
93 octane is available in other areas. Are factory stock vehicles tuned for 91
or 93? The difference can be significant. Are any production cars tuned for 93 versus 91? In
powerful cars, especially with forced induction, just what would the difference
be? An estimate is it can be a ten to thirty horsepower difference.
The last sentence hinting at reliability is
irresponsible. It is implying a vehicle requiring premium is less reliable. Yet
a performance engine is highly engineered with extra robust components. Also a first
tier gas supplier may have a superior formulation in its premium grade. For
instance Shell's V-Power Nitro+ has seven times the government mandated
additive package that is proven to reduce valve deposits, corrosion and cause
less wear versus other brands. That would imply superior reliability.
It should be noted that the testing didn't vary
atmospheric conditions and temperatures. Nor take into account the summer
versus winter grade of gasoline. Engine output varies significantly based on
intake air temperature also called altitude density. It also should be disclosed that vehicles with forced
induction tend to require premium fuel, and not simply recommended unless
specifically noted. Especially when the engine is tuned for performance rather
than economy.
Measuring performance differences demand proper
instrumented testing and procedures. It also requires disclosure of testing
conditions and more than a cherry picked facts and tests.
Link
to Consumer Reports article:
