Drag Illustrated Issue 150, November 2019 | Page 62

DI TECH
UNDER THE VALVE COVERS WITH DART’S
NEW 12-DEGREE LS7 CYLINDER HEAD
Fully CNC machined ports give this head a jewel-
like appearance. They are almost too nice to bolt on
an engine. While a pretty face, this intake port can
deliver 385 cfm at 0.600-inch lift. Those are big-
block Chevy territory numbers.
62 | D r a g
I l l u s t r a t e d | DragIllustrated.com
recently introduced its PRO 1 285cc CNC version
of this head and it’s worthy of a closer look.
To start, let’s take a look at what makes the
LS7 different from an LS3 because it is these
details that makes this cylinder head not entirely
interchangeable with its LS cousins.
Valve angles have been constantly evolving in the
last two decades. The original small-block Chevy
angle (referenced against true vertical) was 23 de-
grees for nearly a half-century before it became
obvious that standing the intake and exhaust valves
closer to vertical would improve airflow by making
the short-side turn in the port gentler. The standard
LS valve angle radically improved the small-block
Chevy from 23 to 15 degrees but the LS7 took that
even further with a push to a 12-degree angle.
Along with this angle change, the intake mani-
fold mounting surface and intake port location
also evolved, which makes the LS7 head unique to
its own valvetrain and intake manifold. This taller
12-degree angle also necessitates its own piston
valve reliefs in order to ensure adequate piston-
to-valve clearance with more aggressive valve lift
numbers that are part of the LS7’s design goals.
With this impressive factory effort, Dart
understood there were many areas where im-
provements could be added that would make
this cylinder head even better for both power
The Pro 1 chambers are also fully CNC machined and
reduced to 66cc volume to enhance compression.
The valves maintain a street-friendly 45-degree
angle for enhanced sealing while not sacrificing flow.
and reliability. When specific horsepower per
cubic inch capabilities with normally aspirated
engines move into the 2.0 hp/ci range, reliability
is an important factor.
Starting with the overall casting, Dart has
retained the stock position for the intake and
exhaust port flanges, valve angle, and valve sizes
to enhance interchangeability with the stock head.
The biggest reason for choosing the Dart head
relates to important additions that the Dart head
offers that do not exist with the factory castings.
Perhaps among the most important is two addi-
Issue 150
W
HEN THE LS7 DEBUTED IN
the 2006 Corvette as the Z06
option, it quickly became the
darling of the LS crowd. Com-
bining 7.0L (427ci) with the best cylinder head
yet for the LS family of engines, it has become
a performance staple for the true believers of
normally aspirated power.
But as good as the production LS7 was and is,
there’s always room for improvement. Dart has