TECH BLACK GOLD
gasoline in the crevice area between the
top ring and the top of the piston and
can pre-ignite when subjected to wide-
open-throttle applications at very low
engine speeds. This is called low-speed
pre-ignition (LSPI). Pre-ignition is not like
detonation. The term describes this very
well because the air/fuel mixture auto-
ignites long before timed spark occurs.
Most often, this auto-ignition occurs
when the piston is low in the cylinder dur-
ing the intake cycle. The result is extreme
cylinder pressure just after the intake valve
closes. As the piston is rising, this extreme
pressure causes instantaneous, cata-
strophic piston damage that often breaks
the ring land right off the piston. There is
no warning for this situation.
This is why GM insists that GDI
engine owners service their engines
with GM dexos1 Gen 2 or the equiva-
lent engine oil to prevent this potential
damage. If an uninformed owner uses
a non-dexos1 Gen 2 oil in his gasoline
direct-injected engine, this may result in
severe damage that will not be covered
under the warranty. Comparing SN oil
such as Castrol 20w50 to Castrol SN+,
you can see that the calcium numbers
drop from the SN’s near 2,100 ppm down
to roughly 500 ppm of the SN+. This is a
reduction of more than 75 percent. Also
note that the magnesium count for the
SN+ oil also increased over the SN ver-
sion. The differences in viscosity do not
affect these additive packages.
While on the topic of detergents, it’s
also worth noting the difference in race
oils compared to oil intended for streetRace oils are intended for pure race cars, like Smokey Yunick’s small-block Camaro, that
are not driven on the street. Race oil can be used on the street, but with low detergent
values, the oil should be changed much more often.10
Some owners
think that
diesel oil is a
less expensive
way to go for
a stout street
engine. But
diesel oils
have also
changed and
the ZDDP
values are
generally only
marginally
higher than
SN oil. A better
approach is to use a purpose-built engine
oil such as those offered by AMSOIL,
Driven, Edelbrock, or others that offer a
Hot Rod oil that combines proper values
of ZDDP and detergents11