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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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Quick inspection of the factory exhaust port shows a massive valve guide boss that hampers flow through the runner.
 

A look into the Edelbrock port indicates that the valve guide boss was designed flush with the roof of the bowl area.
 

The bowl area and valve guide boss on the Performer RPM head are shaped to promote smooth air flow without disruptive turbulence.
 


Stock exhaust bowl and protruding valve guide boss. Sharp short side radius is prohibitive to good flow through the runner.

 

 

 

 

 

 

 

 

 

 

 

 

 

Sources

Edelbrock Corporation
2700 California Street
Torrance, CA 90503

Flow Testing Performed by:
Cylinder Head Dynamics
Tracy, CA
(209) 815-0335

 

 

 

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