Driving Line VOLUME V ISSUE 2 | SPRING 2019 | Page 21

HYDRAULIC ROLLER LIFTERS
Within the valvetrain, the biggest news is this
engine’s use of hydraulic lifters—a first for the 6.7L
Cummins. The elimination of solid roller lifters equates
to quieter valvetrain operation, a longer life for the
valvetrain and the cam, and their self-adjusting nature
means no longer will you have to run the valves every
150,000 miles.
NEW ROCKERS AND HEAD
Under the valve cover—and as you might’ve
HIGHER-FLOWING TURBO
imagined with hydraulic lifters in the mix—the To achieve 1,000 lb-ft of torque at 1,800 rpm, a Holset
rocker arms have no provision for valve adjustment. variable-geometry turbocharger is used, but this one’s a bit
The head itself is all-new, still features a cast-iron different from the same HE351VE bolted to previous engines.
construction and 24-valves per cylinder, but is For improved exhaust flow, taller turbine vanes are utilized in
equipped with upgraded exhaust valves to better the exhaust housing, while the centersection benefits from
cope with additional heat and stiffer valvesprings. heavier-duty bearings. For added efficiency on the compressor
side, a forged-milled compressor wheel (rumored to measure
the same 60mm at the inducer) is employed. At full tilt, the new
Holset can produce 33 psi of boost right off the showroom floor.
DIFFERENT EXHAUST MANIFOLD
Accommodating the new variable-geometry turbo is a fresh exhaust manifold. One of the more
unique-appearing units we’ve seen aboard a Cummins, it mounts the turbocharger in a position that’s
clocked (or tilted) downward, toward the passenger side of the firewall by way of what looks to be a T3
divided flange. As you can see, the turbo will also be bolted between cylinder Nos. 4 and 5, rather than
centrally located between Nos. 3 and 4.
MORE PRESSURE, HIGHER EFFICIENCY,
CLEANER EMISSIONS
Modernizing the common-rail fuel system, the entire arrangement is
still supplied by Bosch, but now the CP4.2 high-pressure fuel pump is used
as opposed to the age-old CP3. Though this twin-piston pump is capable of
producing 39,000 psi, Cummins and Ram have stated that peak injection pressure
will check in around 29,000 psi in this application. Again—and just as is the
case with the CGI block, forged-steel rods and larger head bolts—utilization
of the CP4.2 allows room for future growth. Whether or not the injectors are of
piezo or solenoid style remains to be seen (but we’re leaning toward piezo).
FOR MORE IN-DEPTH DIESEL TECH
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