by Chirag Asaravala. Photography by
the Author and Dart Engineering.
Even though it's been over forty years
since the advent of the small-block Ford "Windsor"series
engines, the popularity of building-up these motors appears
to be greater then ever. Sure Ford has made considerable advancements
in engine technology since the old 289, 302 and 351 motors,
but the complexity of the 4.6 and 5.4 engines, coupled with
performance parts selection and pricing, simply prevent these
motors from gaining popularity with the average garage enthusiast.
There is also the fact that a Windsor motor is easier to crank
big power out of. Stroker kits are cheap, as are power adders.
In fact, in the last several years we're seeing virtually
every Ford enthusiast build a 302 or 351 based stroker when
it comes times for a new motor.
Are you choking?
With so many guys building 347's and 427's, we're unfortunately
also seeing a lot of horsepower left on the table due to poorly
matched cylinder heads. There is no doubt in most guys' minds
that the stock cylinder heads wont cut it for a stroked small-block.
However many of the aftermarket heads are also not a good
choice. Many of the well known heads on the market were designed
around stock displacement figures and their sub-200cc intake
runners are a stretch when it comes to maximizing the potential
of a stroked Ford. Add in a blower and there is no doubt that
bigger gains are probable with a better matched head.
If you've been following our own blown and stroked project
(see High on Carbs) you may at this point be calling us hypocrites.
If so, you'd be right. After all we put ported World Windsor
Jr heads (170cc intake runners and 1.94 valve) on a 331 cid
motor. Then we went and added 8lbs. of boost via a Vortech
supercharger. Sure the motor still cranked out 516 horse to
the wheels, but we know the heads were holding us back. In
fact, making our decision to seek out new heads was made even
easier by the fact the 54cc combustion chamber yields a boost-unfriendly
10.5:1 compression ratio. So when the opportunity came up
to evaluate Dart's new Pro-1 CNC ported heads, we didn't need
to be asked twice. In this article we'll look at the technology
behind the heads. In an upcoming issue we'll bolt the heads
on to our supercharged 331 and see what happens.
Dart of-course is a well known name in the bow-tie world.
Their Chevy stuff has routinely been in NHRA and IHRA winners
circles. Believe it or not, their Honda blocks and heads are
also top players in the import classes. It is only recently
that they've tapped into the Ford market. Fortunately for
Ford fanatics they took their Ford offerings just as seriously
as they do everything else. Dart first introduced all new
Ford 302 and 351 blocks, in iron and aluminum with four bolt
mains and a standard or tall deck heights. These stout blocks
are completely re-designed and, other than dimensional similarities,
they share none of the weaknesses of the stock blocks. In
fact, many power addicts who have inadvertently cracked stock
castings into a pair of four cylinder engines have turned
to Dart iron blocks and gone on to make four digit power figures.
The most recent contribution by Dart to the Ford crowd is
a selection of cylinder heads. Their Pro-1 aluminum heads
are available in "as-cast" form or CNC ported. The
as-cast heads are available as either 170 or 195cc intake
runners (1.94 or 2.02" valve respectively.) The CNC program
takes those volumes up to 210 or 225 cc's. Dart goes with
2.05" or 2.08" valves in the CNC heads respectively.
All heads are setup with 1.60" exhaust valves. Table
1 below outlines the major features of the four available
|Table 1: Dart Pro-1 Cylinder Heads
- Key Figures
Int. Runner Vol.
*Exhaust ports on CNC heads use spread-bolt/SVO
**All heads have 0.135" raised exhaust ports.
Technology makes Power
It's what Dart puts into developing the head that makes us convinced
this is the right head for big-displacement Windsors. The R&D
process relies extensively on the use of a wet-flow bench, a
new technology still only being used and understood in the highest
levels of race engine development. Wet-flow testing is based
on the principle that dry air has vastly different dynamics
than wet air. Conventional thinking has always been to develop
and test cylinder heads using observation and data gathered
from the movement of dry air through the intake and exhaust
runners. It of course stands to reason that on a live engine
the cylinder head must move an atomized mixture of air and fuel.
The physics of how a much denser volume moves through the runners
and around the valves turns out to be significantly different
than the properties of air alone. Consider that air molecules
move at a much faster rate than liquid molecules. Transitions
in the ports and runners may appear to move air efficiently
and with minimal turbulence, but on a wet bench they may show
the liquid falling out of suspension.
A liquid which has the same specific-gravity as fuel is used
rather than gasoline for safety reasons. A dye is added for
visibility. The mixture is injected into the port or cylinder
along with the air stream. As seen in the lead image of this
article, what develops is beautiful tornado-like movement in
the bore and around the valves. It is the analysis of these
vortices and their directions that reveal areas for improvement.
The position of a spark plug, for instance, can cause fuel to
drop out of suspension around the ground strap. This may result
in poor plug performance and flame ignition. Changing the shape
of chamber, or angle of the plug may alleviate this problem.
It is in this way Dart get's one step closer to designing cylinder
heads under empirical engine conditions.
The R&D team at Dart has a distinct advantage over many
other cylinder head manufacturers in that their observations
and improvements from the wet-flow bench can be effectively
implemented into production. Many times the prototype cylinder
head that comes off the production line does not meet the specifications
developed in R&D. This is usually due to the inability to
precisely manufacture the intended design. It's a problem in
any sort of manufacturing, from automotive to electronics. Dart's
Performance Technology Center in Troy, Michigan boasts some
impressive equipment and capabilities. The plant produces 70,000
heads and over 5000 blocks per year. Once the cylinder head
specialists finalize a port design, they use a Coordinate Measuring
Machining (CMM) to precisely measure the dimensions. The resulting
data is then used to create a model which can be edited via
a Computer Aided Design (CAD) program. Once finalized the data
can be transferred into a CNC program to precisely machine the
head using one of fourteen multi-million dollar Makino A77 machining
centers in the Dart facility and the Haas CNC machines for final
port work. The end result is a cylinder head or engine block
that has tolerances as tight as two-thousandths of an inch.