Automotive Engineering - February 2022 - 13

TECHNOLOGY REPORT
Concept
Reality
From
to
In creating the LT6's sophisticated intake manifold, GM powertrain engineers optimized both
volumetric efficiency and package efficiency.
Let the record show that the LT6 is
the most powerful naturally aspirated
V8 ever produced. The 6.6-L 622-hp
(94.2 hp/L) M159 engine energizing the
Mercedes-Benz SLS AMG Black Series
coupe has been bumped down to second
place. While exemplary output
qualifies the Z06 as a legitimate supercar,
bountiful torque is what owners will
most appreciate on the street.
To maximize twist, GM engineers
tapped a phenomenon discovered in
the 19th century by German physicist
Hermann von Helmholtz: that air vibrating
inside a closed chamber at a pressure
slightly above atmospheric produces
the sounds emanating from guitars
and whistles. What we now call
Helmholtz resonance is the technology
underlying the positive intake manifold
pressures that inflate the LT6's torque
curve over a broad rpm range.
Standing tall between this V8's redpainted
cam covers, the LT6's induction
system consists of two molded-nylon
chambers. Two 87-mm throttle bodies
admit air to these manifolds, each of
which has an internal volume of 5.5 liters.
The extensively ribbed, mirror-image
plenums are joined along their
lengths by three 'communicator' valves.
While the driver's right foot operates the
throttles (by wire), the servo-operated
communicator valves are commanded
by the LT6's electronic control module.
Two of the communicators open and
close in tandem while the third operates
on a separate schedule. Inside each
plenum, there are four molded-plastic
AUTOMOTIVE ENGINEERING
trumpets feeding the cylinders with
utmost efficiency. Downstream, each
intake runner splits in two to feed a pair
of titanium intake valves per cylinder.
The mass of the air stream causes pressure
waves to reverberate throughout
the induction system every time an intake
valve closes at the beginning of
the compression stroke.
At wide open throttle, the communicators
remain closed until 2000 rpm
when the paired set opens to foster resonance
between the two plenums. As
rpm and air flow surge, the third valve
snaps open at 5800 rpm. The benefit of
optimizing induction resonance is that
pressure within the plenums rises to help
overfill the cylinders with air.
Instead of the usual arched torque
curve, LT6 output is a nearly flat line
comprised of three short-duration
humps blended by the active induction
system. The apogee is a muscular SAEcertified
460 lb-ft at 6300 rpm.
Volumetric efficiency - the measure of
how well air and exhaust flow through
an engine - tops 110%. In addition to the
above WOT strategy for Sport driving,
the LT6's control module offers five additional
collaborator-opening programs
for the Z06's Tour, Stealth, and Track
driving modes.
Herr von Helmholtz, born two centuries
ago, clearly deserves a respectful
tip of the hat to celebrate his birthday,
and to acknowledge those contributions
that enabled the small-block V8's
latest leap forward.
Don Sherman
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Automotive Engineering - February 2022

Table of Contents for the Digital Edition of Automotive Engineering - February 2022