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Exhaust
Port Analysis
Airflow through
a cylinder head is more sensitive to shape than size.
Sudden changes in direction, volume, or shape do not
encourage good flow. For these reasons the factory 429
casting did not fair well in our exhaust flow test.
To demonstrate the difference in exhaust runner shape
and contour between the Edelbrock head and the factory
429 head we took silicone molds of both heads.
 A
mold of the D2VE-AA exhaust runner clearly shows why
exhaust flow numbers are poor. Constriction due to the
massive valve guide boss hampers flow along the top
of the runner. Protrusion of the pushrod passage pinches
the runner. Perhaps most crucial is the steep angle
of the short turn radius. The sharp turn disrupts the
flow of exhaust gasses transitioning from the bowl into
to the runner. Gas flow becomes turbulent in this area
which further hinders flow. The overall volume of the
runner is insufficient to support the amount of air
the intake runner is bringing in. Exhaust to Intake
flow ratio drops to 59% in the mid-lift range.
 It
doesn't require much more than basic physics to see
why the Edelbrock exhaust port flows over 20% greater
than stock. It is important to note that this is not
achieved by simply making the runner larger. The short
turn radius is laid down at a less severe angle. The
valve guide boss is cut flush with the roof of the bowl
area. The overall "macaroni" shape of this
exhaust runner promote smooth laminar air flow. Perhaps
most impressive is that the results are achieved without
modifying the exhaust port location.
Design Strategy Q & A
Edelbrock Engineer, Jim Dralle, answers our questions
regarding the development of the Performer RPM 460 Cylinder
Head.
Q: FordMuscle flow tested
the Performer RPM 460 Cylinder Head against a standard
factory iron head (D2VE-AA). We were surprised to find
that the factory 429 head flowed quite well on the intake
side. The Edelbrock head flowed as advertised with excellent
improvements over the factory head on the exhaust side.
From this data we concluded that a great deal of the
development of the Performer RPM 460 head was spent
on improving the exhaust runner to achieve a better
balance with the already well-designed factory intake
runner. Would you say this conclusion is accurate?
A:
I would say this conclusion is accurate. I have always
found it funny that the highest performance stage in
the Ford performance handbook for 429 Fords is to remove
the Cobra-Jet heads in favor of ported Standard heads
modified to fit with a CJ intake manifold. The layout
of the 460 Ford engine favors the intake port design.
The exhaust port with the exit flange position given
by the stock design made it very challenging to design
an exhaust port that performs well. Designing ports
that can be consistently manufactured is also a big
part of the development process.
Q: What
was done to the Performer RPM 460 Head to improve the
exhaust flow over the factory design?
A: One of our best
port designers has said "it is not important where
you
remove material in the port, it is were you leave the
material that is most
important". The short turn area is the most critical.
If it is too-high
the flow will separate. If it is too-low, even if it
may flow well, the port
will not be consistently manufacturable. If I was going
to detail only one
area of the ports it would be the exhaust short turn
area. Careful
detailing of this area will yield more power potential.
Q: Did the development
of the Performer RPM 460 Cylinder Head require any compromise?
A:
The most difficult application for which to design a
cylinder head is an
application that is required to mate with stock intake
manifolds and exhaust headers. The fact that the 460
Ford engine was designed with two different intake port
configurations (standard and Cobra-Jet) definitely created
some issues that had to be decided at the beginning
of the design process. In general the head is designed
specifically for the largest customer base but material
is placed in the the head at the right locations to
allow easy modifications that will suit other potential
users. Combustion chamber
size was also another issue that presented itself early
in the design process. Some customers wanted an CJ size
chamber and some desired a larger volume chamber that
would produce lower compression ratios with stock configuration
pistons. In this case we decided to design and offer
two different combustion chambers.
Conclusion
Whether you are building a 460 or not, when having a
pair of your own heads power tuned or when shopping
for aftermarket heads, keep in mind that the areas of
a runner that are the most difficult to see and reach
offer the greatest performance gains. In the case of
a cylinder head modifier, this is where they will spend
the most time massaging the head. In the case of the
manufacturer, this is most likely where the greatest
Research and Development work will be performed. Sure,
when we received Edelbrock's Performer RPM 460 heads
for our recent BBF build we knew we were making a leap
towards better performance. However, it wasn't until
we compared the head by flow testing and taking molds
of the runners that we realized our decision was a sound
one. Watch for FordMuscle's continuation of the article
Streetwise 460 for real world testing of the Edelbrock
Performer RPM 460 cylinder head. 
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