Affordable Port Work
Affordable factory head porting is available from PowerHeads in Southern California. PowerHeads uses CNC technology to hog out the intake and exhaust ports on 260, 289, 302, and 351W heads to make them one of the greatest performance values in the industry. For under $1,000, PowerHeads takes your cylinder-head castings and after CNC-port work along with hand-massaging finish work, vastly improves performance. PowerHeads will install your valve springs at the same time. You can provide the head cores or PowerHeads can provide them. The choice is yours. If you want your cylinder heads ported and returned to you, please advise PowerHeads and document your request. If you don't, expect a different set of heads.
PowerHeads begins CNC port work at the bowls as shown, opening... | 
...them before moving on to the ports. |
This creates a smooth airway to the valve face and seat. | 
Once the port bowls and valve pockets are cut, the CNC process moves on to the intake and exhaust ports. |
This process cuts out all of the bumps and irregularities to improve flow. | 
For example, this process completely removes the Thermactor hump in smog heads, making them usable. |
The finishing process includes hand grinding for a smooth finish. The CNC process makes this affordable because labor is greatly reduced. Finish work doesn't take long and yields professional results. | 
PowerHeads wraps up the port work with a valve job that includes new guides, hardened exhaust-valve seats, valves, seals, and springs. |
Here's another example of core shift during the casting process that causes exhaust-port irregularities. PowerHeads has worked this port as much as it can. This is why proper head selection is so important to good porting.
Wild, Weird Science
The science of port work is little more than common sense. Think of the flow of air and fuel as water. Water ripples and aerates as it cruises over surfaces. So do air and fuel droplets. Our objectives are smooth surfaces and turns. We want increased velocity while we're at it. Velocity is simply air speed, how fast air and fuel move through an intake port. On the exhaust side, we want hot gasses to leave quickly without a traffic jam. We actually want those hot gasses to help with intake flow when we have valve overlap.
Matchmaker, Matchmaker
Intake manifolds and carburetors are just as significant to porting as the human eye and a grinder. Carburetors must match intake manifolds. Intake manifolds must match cylinder heads. When perfectly matched, airflow becomes smooth and plentiful. We cannot overemphasize proper port matching.
Flow begins at the carburetor base and intake plenum. Sharp edges need to be rounded, properly radiused to where they are smooth. Mark treats this area just like he does the short turn of a port. Keep the ride smooth around corners. | 
Another consideration is intake runners. Very few of them are straight, especially with dual-plane high-rise manifolds. The vintage Cobra high-rise manifold is based on Edelbrock's F4B manifold of the period with large runners that offer good medium- and high-range torque. Runner size varies a lot, which also affects porting. There's not much you can do about runner size. However, you can make the transition smoother. |
When you're shopping intake manifolds, be sure port size is close to cylinder-head port size. Port matching is only effective when port sizes are similar already. Ideally, manifold port size will be a pinch large before porting begins. | |