arine engine specialist
Mercury is building an exotic,
Chevy-based dual-overhead-
camshaft V-8.
That’s the story lead you might have read
just about 30 years ago when the company
was tasked with assembling the C4 ZR-1’s
DOHC LT5 engine. Selected for a number of
reasons, including its prowess with alumi-
num castings and low-volume production
efficiency, Mercury’s MerCruiser division
handbuilt all of the first- (385hp) and
second-generation (405hp) LT5 engines.
Three decades later, the company
is at it again ... sort of. The company’s
Mercury Racing division is, indeed, build-
ing new DOHC V-8 engines, but rather
than doing it for a production Chevrolet
product, they’re building a standalone auto-
motive crate engine package dubbed the
SB4 7.0, which is offered through the hot rod
builders at Roadster Shop.
In a nutshell, the SB4 7.0 uses a GM LS
foundation (the LS7 cylinder block) with an
all-new, custom-designed set of four-valve,
dual-overhead-camshaft cylinder heads.
The result is a naturally aspirated LS-based
engine that spins to 8,000 rpm and pro-
duces 750 horsepower. Chevrolet relies on a
supercharger to get the same output for the
LT5 engine in the Corvette ZR1.
In fact, the SB4 7.0 clocks in at 1.75 horse-
power per cubic inch, versus the original
LT5’s 1.07 horses per cube. That’s 63 per-
cent greater horsepower per displacement,
but it’s not surprising for anyone who runs
the waves as well as the highway because
Mercury has been building its own DOHC,
high-rpm marine engines for a long time.
They’ve simply funneled that experience
from the launch ramp to the street.
“This engine represents the best of
BY PETER MURPHY (^) I PHOTOGRAPHY BY STEVEN RUPP
DOHC Déjà Vu
Mercury Marine and Roadster Shop team up for a four-cam
crate engine with echoes of the original LT5 ZR-1 engine
[ TECH]
everything in a restomod or Pro Touring
crate engine,” says Phil Gerber, owner
of Roadster Shop, the exclusive retailer
for the SB4 7.0. “It takes LS-based perfor-
mance to the next level, with a familiar
foundation that is already supported in
the aftermarket when it comes to engine
mounts, transmissions and the like. It
also offers a distinctive appearance that’s
unlike anything else.”
That’s for sure. The extra-wide cam
covers lend the engine a decidedly high-
tech, exotic look that’s complemented
by a custom intake manifold featuring a
pair of throttle bodies. It would look pretty
amazing in the engine compartment of a
C1 or C2 restomod.
The unique cylinder heads, which are
cast by Edelbrock, feature four valves per
cylinder and a robust, high-rpm valvetrain.
While not unique to DOHC designs, the
heads are somewhat unique to perfor-
mance V-8 engines because they employ
internal cam-to-cam drive via straight-cut
gears. One gear in each head is a scissors
gear design, which allows for zero effective