Chrysler’s Slant 6 of 1960-1987 is remembered today as one of the most
rugged and dependable engines in Motor City history. Here’s the story behind
the indestructible Mopar six.
All
through the 1950s, the Chrysler Corporation was noted for its engineering
leadership and cutting-edge, high-performance V8 engines like the legendary
Hemi. But oddly, the automaker’s six-cylinder offerings were antique L-head
designs that dated back to well before World War II.
Overweight,
bulky, and inefficient, the creaky old L-Head was totally unsuited for the
all-new Valiant compact being readied for the 1960 model year. Chrysler’s
engine specialists stepped up and designed an equally new and innovative
powerplant for the Valiant, the Slant 6, which was then adopted by the company
across the board. Along the way, the Slant 6 developed a reputation as one of
the most rugged and reliable engines the Motor City has ever produced. Here’s
the story.
Lead engineer
on the Slant 6 project was Chrysler engine wizard Willem Weertman, then the
company’s manager of engine design, and he began with a clean sheet of paper,
taking nothing from the old flathead sixes. Of course, the engine’s most
notable feature was its canted block with the cylinders laid over 30 degrees to
the right. This permitted a significantly lower cowl and hood height, a key
element in the Valiant’s distinctive styling, and it also made room for long,
straight intake manifold runners for improved fuel/air distribution, a
traditional trouble spot in inline-six layouts.
While
everyone knows the Slant 6 name today, it took a few years to catch on
completely, even within the company. Initially, Plymouth branded the engine as
the 30-D, referring to the cylinder bank angle—not nearly as catchy, we can
agree. Two displacements were initially offered: a 170 CID model for the
Valiant with a 3.40-in. bore and 3.125-in. stroke, and the 225 CID unit, which
used a long 4.125-in. stroke and a tall-deck block to power the full-size
sedans.
While the
canted block provided an obvious advantage in reduced height, there was another
less obvious but equally important benefit. With the cylinders laid over 30
degrees, the water pump could be placed alongside the block instead of in
front, shortening the engine’s footprint by a good four inches. Four main
bearings also helped to keep engine length to a minimum, while the sturdy,
deep-skirted block and short, stiff crankshaft ensured solid reliability and a
long service life.
The big
DC generator on this 1960 Slant 6 display engine indicates a full-size sedan
application. The Valiant was offered from the start with a compact AC
alternator. For the initial 1960 model year, the 170 CID version was rated at
101 hp at 4400 rpm, while the long-stroke 225 CID unit produced 145 hp at 4000
rpm.
Between
1961 and 1963, Chrysler produced more than 50,000 Slant 6 engines using an
advanced die-cast aluminum block. Manufactured only in the raised-deck 225 CID
version, this piece proved to be somewhat more trouble-prone than the standard
iron block, with cast-in-place ferrous cylinder liners that tended to separate
from the aluminium block casting. A special head gasket was also required.
Some of
these aluminum blocks also included provisions for hydraulic valve lifters,
though they were not so equipped. Sort of an anachronism in this regard, the
Slant Six did not adopt hydraulic valve lifters until 1981. All previous
versions employed old-fashioned solid lifters that required periodic
adjustment.
Quickly
developing a reputation for ruggedness and dependability, the Slant 6 was soon
adapted to all sorts of marine, industrial, and agricultural applications—they
could turn up almost anywhere. This Australian advertisement shows a 225 CID,
119 hp Slant 6 paired to a Chrysler Marine outdrive unit. Slant 6 Chryslers are
also commonly found powering portable welders, self-propelled combines, and
irrigation pumps. Many are
still in operation today.
While not a performance engine per se, the Slant 6 did
find its way into a number of performance applications. Here’s the installation
in Tex Smith’s famed XR6 hot rod, winner of the 1963 AMBR Award, which sports
three Weber sidedraft carbs and fabricated tubular headers. (Read the feature here.)
Chrysler
offered the Hyper-Pak, an over-the-counter performance package sold by Dodge
and Plymouth dealer parts departments. The setup included a long-ram intake
manifold, special exhaust manifolds, domed pistons, and a special camshaft,
boosting the output of the 170 CID Slant 6 to 148 hp or more. Updated versions
of the trick pieces are now available in the performance aftermarket.
The Slant
6 was continually updated throughout the ’70s and ’80s—this later version
sports a thermostatic air cleaner, air injection pump, EGR valve, and other
familiar hardware of the Detroit emissions era. The venerable engine handled
the modifications well, though they didn’t do the net output any good. In 1974
a 198 CID version (destroked for fuel economy) was introduced, and in 1977-78
there was a 225 CID Super Six variant that boasted a Carter two-barrel
carburetor for a little extra punch.
One of
the longer-running engine families of the era, the Slant 6 remained in
production until 1983 in passenger cars and until 1987 in trucks, and not until
1991 was the engine finally discontinued in industrial applications. Thus
closed the book on one of Detroit’s most beloved engines.
An
interesting footnote to the Slant 6 story: Not many Detroit concept cars
are motivated by a new engine design, but in 1960, Chrysler vice president of
styling Virgil Exner created the Plymouth XNR prototype sports car. The
concept’s unusual asymmetric design elements were directly inspired by the
Slant 6’s offset engine configuration. This photo, as well as the photo of the
XNR’s engine that leads this feature, are courtesy of RM Sotheby’s.
Source: https://macsmotorcitygarage.com/leaning-tower-of-power-the-chrysler-slant-6-story/
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