Driving Line VOLUME V ISSUE 2 | SPRING 2019 | Page 20

STRONGER BLOCK
Getting away from gray cast iron for the first time in this engine’s
history, the high-output 6.7L Cummins now sports a compacted
graphite iron (CGI) crankcase from Tupy, which is perfect for the
higher cylinder pressure this engine likely sees over previous
versions. Added hardness and fatigue strength, better ductility
and improved tensile strength, and substantial weight savings are
all benefits of casting a block from CGI (this block is 60 pounds
lighter). We don’t know the exact stats on the Cummins’ crankcase,
but we do know that CGI can be as much as 75-percent stronger
than conventional gray iron. A new, stronger alloy crankshaft with
a 10-bolt crank flange is secured inside the deep-skirt block.
LIGHTER, LOWER
COMPRESSION PISTONS
New cast-aluminum pistons (right) with low-friction rings
and larger-diameter wristpins improve durability while lightening
the rotating assembly. The H.O. mill’s compression ratio also
checks in at 16.2:1, versus 17.3:1 previously. Beneath the
pistons, you’ll find that Cummins has gone back to forged-
steel connecting rods (rather than powdered metal), which
further justifies our theory that this new engine was designed
with plenty of room for future growth in terms of horsepower
and torque.
OILING AND COOLING
IMPROVEMENTS
To keep operating temps and lubrication in check
with 17-plus tons in tow and four-digit torque on tap,
the oiling and cooling systems have been upgraded. A
higher-volume oil pump and water pump made the cut
and are most likely accompanied by a larger radiator and
higher-capacity engine fan. For additional weight savings
(as requested by Ram), the oil and water pumps sit in
aluminum housings.
LARGER HEAD BOLTS
While we don’t have the exact measurements
at our disposal, we can deduce that the diameter of
the head bolts holding the new cylinder head to the
CGI block are larger in diameter. Our educated guess
is that Cummins increased the head-bolt diameter
from 12mm (left) to 14mm (right). The larger-diameter
fasteners will be vital in keeping the head gasket
alive for hundreds of thousands of miles with more
cylinder pressure in the mix.
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