09
The camshafts are made of billet steel and carburized
(case-hardened) on all running surfaces for excep-
tional wear resistance. They are also polished and REM surface-
finished to help reduce friction.
10
On each head, the exhaust cam drives the intake cam
with a scissor-type action that ensures the pair are
phased properly at all times and engine speeds. The design
also helps keep the heads relatively narrow.11
The cam drive system has reduc-
tion in two stages to keep belt loads
as low as possible. Together, they yield
the required 2:1 overall ratio. The chain
primary drive has a Mercury-designed
hydraulic tensing system to maintain sta-
bility at 8,000 rpm, while the cam-drive
belt pulleys (on the exhaust cams) have
integrated pendulum absorbers to keep
the timing drive stable at high engine
speeds and high valve accelerations.
14
The port-injected engine uses
60-lb/hr fuel injectors.12
The valvetrain relies on a shaft-
mounted, end-pivot finger-follower
design, with adjustment shims between
each finger and the respective valve
stem tip. The fingers are held in place,
laterally, by coil springs on the rocker
shafts. The fingers themselves are Mer-
cury’s own design and are made of
investment cast steel, then case-hard-
ened, ground REM surface-finished and
DLC-coated (diamond-like coating).15
Like the heads, the cast-aluminum
intake manifold was designed with
computational fluid dynamics for opti-
mal airflow. A pair of 80mm electroni-
cally controlled throttle bodies is one of
the engine’s distinctive design elements.13
The
cylin-
der head has
a bedplate
design, mean-
ing it does
not have indi-
vidual cam
caps. Instead, the cam caps and outer
head structure are all one bedplate (also
known as a ladder frame). Because the
bedplate does not have enough fasten-
ers to hold it down against flexing from
valvespring force, when the top cover is
removed, the top cover’s bolts do dou-
ble duty: they hold the top cover on
and clamp the cylinder head’s bedplate
to the head. It makes setting lash a bit
harder, but it saves weight because of the
reduced fastener count. The steel girdle
seen atop the head here is used when
setting valve lash.16
The curved, L-shaped component
at the right of the photo is an oil
drain-back tube and there’s one at the
rear of each cylinder head. The engine
also uses a Holley oil pan.54 VETTE 19.0 4
[ TECH]