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Exhaust Ports
Once you've gotten a feel for the carbide cutter, you can start with the exhaust ports. The first step is to mark the gasket match boundary. This will define how much you should open up the port. You should use the exhaust header gasket which best matches your headers. It is critical that the exhaust port not be ported larger than the size of the header flange opening. If the exhaust port is larger than the header flange, gases exiting the port will hit the flange and create turbulence. The objective is to have a smooth transition from head to header.

There are alot of cheap paper header gaskets out there, and most of them have awkward port sizes. We've found the Fel Pro 1415, as well as the Mr. Gasket Ultra Seal to be the best gaskets, in terms of port size (1.25" x 1.48") and also durability. Mount the gaskets using a couple of header bolts and some tape so that all of the holes are evenly spaced around your ports. Then use permanent ink marker to trace the edges of the gasket ports to the head surface. Finally, you can use a sharp scribe to make permanent edge limit markings.

You should also check the gasket against the headers, and port the flanges to match the gasket. Most headers have a fair amount of welding slag and excess flange material hanging into the pipe from the manufacturer. Cleaning this up will help significantly, but be cautious not to grind the welds or flange too thin.

Now that you have your outlines ready- start your grinder! The exhaust ports are the best place to start. Looking at the 'before' picture to the right, you can see the typical restrictions that are in most Windsor heads. Typically there is a lip on the roof at the mating surface, even as much as 1/16" piece of flash hanging there. If you have '66 or later heads with the smog bumps, they will be first to go. This is where you really should use a carbide bit. If you can combine that with a high-speed grinder, those bumps will be history in no time. This is another place for learning the feel of your tools. By the time you cut down all eight bumps you will be more confident in your abilities. Take the bumps down until they are even with the surrounding roof.

The valve guide boss is next. It does not protrude far into the port, but it does form an unneccesary obstruction, so grind it down. Most machinists and professional porters agree that there is plenty of iron above the port to secure the valve guide. Some shops will cut the new bronze valve guide flush with the roof, others leave it the full length. It's really a matter of preference. On aluminum heads, however, a full guide is recommened for stability.

There are many "generic" porting articles that say to only go about an inch into the exhaust port. That may be true for Chevys but is absolutely wrong for the stock Windsor heads. To make the walls and roof straight you will need to go almost all the way to the back of the runner. If you check your stock exhaust runner you will see, and feel, how it is actually smallest at the opening and larger at the back of the bowl. This is backwards from what it should be. You want your exhaust port to stay a consistent shape or even expand a small amount so flow is not impeded. Unlike the intake port, which has cooler air/fuel mixture being drawn in by the vacuum created from the downward moving piston, the exhaust gases are very hot and under high pressure and will take the fastest way out. The straightest port is the best flowing port. When you finish gasket matching, the walls, floor, and roof should either be straight or taper larger as you move from the bowl out to the port.

The runner then turns up a few down degrees to the valve seat. If you look at the pictures of our ported head you can see that it is almost a straight line from the port opening to the back of the bowl. The exhaust gases will flow best if they don't have to change directions. By the time you have made a nice straight roof you will have hours of grinding time under your belt.

Finally, the bowls need attention. Referring to the picture of the stock bowls, there are a couple of major ridges in the exhaust port throat that need removal. The first one is on the short turn radius. This ridge only needs to be ground smooth. Do not change the shape of the turn! This is where experience counts and inexperience can get you into trouble. If the radius is reduced too far your flow will suffer because the gas will have too tight a turn to make and become turbulent, slowing the gas velocity. So our advice is to stick with the sanding rolls when working the short-turn radius in both ports. There will be small ridges just under the valve seat from the machining process. Smooth these with the sanding rolls. Remember, you should get a three-angle valve job after you're done porting.

The last step will be creating the proper surface finish. For most applications going over the entire port and bowl area with the 80 grit (or "Fine") sanding rolls will suffice. For that last little bit of flow you can polish the surfaces to a mirror finish using a carbide impregnated rubber bit in the Dremel tool.


Bowls Before:
Shown here is a typical combustion chamber on a stock Ford windsor head.
Note the protruding valve guide boss. Grinding this flush with roof will increase flow dramatically.

Also note the ridges below the valve seat. Smoothing these out helps reduce turbulance; getting the gas through the head faster.

Tip:
Use your index finger to probe the stock ports. Follow the path of the gasses. On the exhaust port, stick your finger in through the bowl, and on the intake side, start from the intake port opening. Get a feel for all the obstructions, the surface of the ports, the ridges, bumps, and irregularities. Everything that feels like an obstruction to your finger, is impeding air flow, and needs to be worked on.

Bowls After:
Here is a close up of the exhaust bowl. The valve guide boss has been blended into the roof. The ridges in the throat area have been smoothed down. The entire exhaust port has a slight taper from bowl to exit. Finally the entire area is polished with fine grit sanding rolls.
Imagine how different this port would feel with your fingers, compared to the stock port.



(Flow Bench Results)

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Exhaust Before.
This picture of a typical stock exhaust port shows several important features:

1) Circled in yellow is
the "Thermactor bump". This obstruction on the roof of most post-1966 Ford Windsor heads is a huge impediment to exiting gasses. Grind this out!

2) The grey stem in the back of the port is the valve. Note the valve guide boss. This too can be ground even with the roof. There is plenty of above the port to support the valve guide.

3) Finally, look at the shiny clean border all the way around the exhaust port and header bolts. This is left by the exhaust gasket. While the intent here wasn't to scribe a "gasket match" boundary, this picture nevertheless shows you just how much material can be removed from the exhaust port. You can safely grind away all out to the edge of the black sooty border.

 

view larger
Exhaust After.
Looking at our home-ported head, you see the Thermactor bump is history. If you look hard you can barely make out where the valve guide boss used to be.

Compared to the 'before' photo, our port is opened up to match the size of the header gasket.

Note that the entire runner emmulates as straight of a line as posssible from the bowl to the port opening. This will result in the fasted possible exit of the exhaust gasses from the combustion chamber.

 

 


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