Cadillac 2007 XLR - Manual (Page 366)

Gasoline Octane
If your vehicle has the 4.6L V8 engine (VIN
Code A), use premium unleaded gasoline with a
posted octane rating of 91 or higher. You may also
use regular unleaded gasoline rated at 87
octane or higher, but your vehicle’s acceleration
may be slightly reduced, and you may notice
a slight audible knocking noise, commonly referred
to as spark knock. If the octane is less than 87,
you may notice a heavy knocking noise when you
drive. If this occurs, use a gasoline rated at 87
octane or higher as soon as possible. Otherwise,
you might damage your engine. If you are
using gasoline rated at 87 octane or higher and
you hear heavy knocking, your engine needs
service.
If your vehicle has the 4.4L V8 engine (VIN
Code D), use premium unleaded gasoline with a
posted octane rating of 91 or higher. For best
performance, use premium unleaded gasoline with
a posted octane rating of 93. In an emergency,
you can use regular unleaded gasoline with an
octane rating of 87 or higher. If 87 octane fuel is
used, do not perform any aggressive driving
maneuvers such as wide open throttle applications.
You may also hear audible spark knock during
acceleration. Refill your tank with premium fuel as
soon as possible to avoid damaging your
engine. If you are using gasoline rated at 91
octane or higher and you hear heavy knocking,
your engine needs service.
Gasoline Specifications
At a minimum, gasoline should meet ASTM
specification D 4814 in the United States or
CAN/CGSB-3.5 in Canada. Some gasolines may
contain an octane-enhancing additive called
methylcyclopentadienyl manganese tricarbonyl
(MMT). General Motors recommends against the
use of gasolines containing MMT. See Additives
on page 367 for additional information.
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