Chris Grayson's (of MC2Racing) Guide to a Reasonably Priced, Street Setup for Handling

Chris Grayson has been involved in Merkur XR4Ti performance for a very long time. He formed MC2Racing to provide quality performance parts t...

Saturday, December 12, 2020

Throwback: Head Porting By David Godfrey

David Godfrey's Article About Head Porting

David Godfrey is somewhat of a legend in the XR4Ti circles, being a prolific problem solver and fabricator, he came up with some good solutions to deficiencies in the XR4Ti platform. In this case, he's documented how he thought about and went through with getting the head ported. 

David no longer maintains his website, so I pulled this out of the Internet archives to give it a new place to live, so people can see it, and take some inspiration from his ideas. 



I proposed to the MCA folks giving this seminar so that perhaps some of the DIY types might have a game plan on a possible way to port their own cylinder head. Hopefully the results of this seminar will be that this individual will be able to act as their own general contractor and be able to oversee the cylinder head rebuild.


I have been tinkering with cars, motorcycles, bicycles, radio control sailplanes, etc, for all my life. I have probably built at least 25 motors, some of them when I was working for a speed shop but most of them for myself. I have never built a motor for my personal use, even on a daily driver, where I did not port the cylinder head. I ran the IHRA points circuit and set 6 national record with a modified compact Pinto. This car had a 2.0L normal aspirated motor coupled to a Doug Nash 5 speed. Prior to that I ran a 67 Shelby GT500 with a boss 351 Cleveland motor. This car ran in what was then called formula 2, B modified, which is a single 4-barrel class. There were restrictions on the amount the motor could be modified, and, of interest to this topic, particularly how much the heads could be modified.


Porting cylinder heads is rewarding but nasty work. Running the die grinder for the amount of time required is a carpal tunnel syndrome sufferer's nightmare. I know cause I have it! As a minimum ear plugs, safety glasses, and a mask is required.

Since March I have ported three 2.3 heads and manifolds and have been to the eye Dr. twice to get particles removed from my eyes. This is with using safety glasses. The first time a shaving got up underneath my glasses. I switched to protective goggles and got a particle in my eye anyway. I think it occurred when I pulled the goggles off and something fell out of my hair. Now I brush out my hair and dust of my clothes before I pull the protective gear off.


The main tool required is some type of grinder. I have used both electric and air powered grinders and my current preference is the air-powered grinder. I have a 110v 1-horse compressor that works fine. It runs all the time, but it works well.

For rough in type work I have several different types of carbide burrs. Note there are burrs for aluminum and steel. Aluminum burrs have fewer teeth. If you use a steel burr on aluminum be prepared to spend a lot of time cleaning the aluminum out. If you use an aluminum burr on steel it will chatter and dull quicker.

I also have several different shapes of burrs on different length stems. I tend to do most of the rough in work with the large "tree" shaped burr.

A couple of old valves have been ground down on the face that I use to protect the valve seats when working the combustion chamber.

I use several different types of cartridge or sanding rolls for the finish work. I tend to use a lot of the 3/8 diameter 60 grit rolls when working the valve pocket. I will go to 180 and 240 grit rolls for final polish.

When you are using the rolls remember that most of the work is done on the tip of the roll. They will were out fairly quickly so change them often. A worn out 60-grit roll does not become a 120 or finer grit roll; it becomes a worn out 60-grit roll. The "teeth" wear down and the cutting action becomes more of a burnishing effect. One can waste a lot of time trying to use a dulled cartridge roll.

The big diameter rolls are handy for smoothing out bumps and removing casting flash. If there is a ridge in the port such as where the mold seams meet the small diameter rolls will tend to fall on one side or the other. The big diameter rolls really do a nice job of making things round.

I also have a couple of different length arbors. The long arbor is used for intake manifolds and working the short side radius. The short ones are used for general work. The disadvantage of the long arbor is it tends to vibrate more, especially with large diameter rolls.

You will see porting kits from places like Summit or Jegs. I would suggest you get your supplies from an industrial supply house or MSC or McMaster Carr. I buy the 3/8 diameter rolls in bags of 100. Also get a roll of emery cloth to use for smoothing the short side radius.


Most of ya'll probably don't remember this, but back in the early 80's both the NHRA and IHRA had single 4-barrel modified classes. In NHRA they called it super modified. IHRA called it formula 2. These classes had restrictions on the amount of cylinder head work that could be done. They would let you match the intake manifold gasket to the head, but the matched area could not extend more than 1/2" into the port. The bowl are could be worked also, but again, the reworked area could not extend into the port more that 1/2" from the valve seat. The combustion chambers could be reworked as needed. It ended up that the main benefits or power increase was due to rework within 1/2" from the valve seat. This holds true for most cylinder heads.

You can see from the head sections I have that the port is very flat, actually it is parallel to the head gasket surface. You can also see how much material there is around each port. The amount of benefit one can get from porting is limited due to the starting point. No amount of grinding is going to transform this casting into a super breather comparable to today's motors. A significant increase can be made, but recognize the limitations of the design from the start.

Port layout

Recognize that no amount of grinding is going make this into a Vtech head, so instead concentrate on removing obstructions to flow around the valve seat. Keeping with the super-modified rules, reworking the port within 1/2" of the valve seat, is not a bad rule of thumb. The 2.3 head is pretty ugly in this area and the main benefits to be gained will occur from working this area.

When Rick Byrnes went to the Esslinger head on his race car he got a 20% power increase using the same valve size and cam. This increase is due entirely to the port shape. In Rick's case he was able to run 20% less boost and get the same power. The overall shape of the 2.3 head has been determined by Ford. All you can do is try to clean it up. Where I live folks have been racing mini-stockers for years with 2.0 and 2.3 Ford motors. I have seen some pretty radically modified heads show up at my friend's machine shop. These include heads that have had steel tubes furnace brazed in place to change the angle where the port enters the head. Some of these modifications had varying degrees of success, but most were a lot of trouble for little gain. This is due to the base, early 1970-'s design of the head.

I tend to leave the intake port shape and general size alone and except for the bowl area just clean it up. You can see from the head sections that there is no a lot one can do to change the port shape. The exhaust ports get more work. I increase the diameter of the port and reposition it upward. I use to do this by hand, but on the last two heads I've done I did the majority of the work on a milling machine. I set the head up and bored the port to 1.375" diameter with the bottom of the diameter tangent to the existing port floor. I took this to a depth of 1.10" into the port. The remainder of the port was worked with carbide tools and cartridge rolls.

Combustion Chamber Layout

The 1/2" valve seat rule of thumb works on the combustion chamber side as well. There are some obstructions that can be removed or blended and some you can't. The main restriction to flow, especially at low valve lift, is the side of the chamber next to the quench area. This restriction gets worse when big valves are installed. Opening this area up is called unshrouding the valves. One thing you can't to anything about is where the cylinder shrouds the valve. A big valve makes the shrouding worse in this area.

When reworking the combustion chamber I put dykem blue on the gasket surface and then bolt it to a bare block. I then reach up into the cylinder and scribe the cylinder bore to the head. This scribe line defines the "stay out zone". I then scribe lines on the head indicating where I will unshroud the valves. The rough in work is done with the small round and tree shaped carbide cutters. I then use the cartridge rolls to blend and smooth all the surfaces.

Intake Manifolds

There are several areas in the intake manifolds to rework. The main problem area is the ports at the head surface are way undersize. Ford did this to ensure there was no obstruction into the port. The manifold can be opened up significantly to match the head.

To transfer the head port shape accurately to the intake I use a template. Do not try to match to the intake gasket! It is grossly oversize. If the head and manifold are matched to the gasket you will end up with a configuration where the charge air will expand and then be funneled back down. The expanding part is not bad, but the squeezing back down is.

I make a template of the ports by taping a piece of card stock to the head and then using an Exacto knife cut out the port shape and a couple of the mounting holes. With the template still taped to the head I bolt on the intake manifold and scribe or cut the template to match the outside of the intake mounting flange. This gives me a good point of reference of where to place the template on the manifold. I then remove the manifold and template, put dykem blue on the manifold gasket surface, align the template and scribe the port shape to the manifold. Using the carbide cutters the intake can quickly be opened up. After grinding on cast iron one can appreciate working with aluminum.

The lower intake has pretty severe projections into the port on runners 2 & 3 where the fuel injectors plug in. I remove these by TIG welding the outside of the manifold and then smoothing out the bumps inside the ports. They cannot be completely removed, but they can be made a lot better. Epoxy such as Devcon or JB weld can be used instead of welding. Both these epoxies will hold up well.

The runner junction in the upper manifold is another ugly area. I gain access to it by cutting the manifold apart. The junction can then be smoothed and the manifold TIG welded back together. Some folks remove runner walls completely. This would not be my choice for a street motor, but if I were to do so I would still cut the manifold apart to make it easier to get to.

Exhaust manifold

The exhaust manifold ports can be enlarged to match the head by using a template similar to the intake manifold. There are some rather nasty corners and bumps to clean up at the port. I do this using the large round and tree shaped carbide burr.

The opening to the turbo needs to be matched to the stainless steel gasket. This is a lot of grinding but well worth it.

One area to look at is the turbo outlet. I open this up to the inside diameter of the down pipe.

Head Rework Process

I mentioned that the purpose of this seminar was to provide the DIY types with enough info to do their own head porting and oversee the machine work. The steps I use are as follows.

1) Disassembly and Inspection

No special tools are required to take the head apart. A valve spring compressor is handy, but not necessary. A large socket and whuppit (hammer for city folk) can be used to remove the valve keepers. Placing the head on a surface with the springs pointing up. Put the socket on the retainers and smack it with the whuppit. The retainers will pop out. Remove the springs and valves and inspect the seats for cracks. Some cracks can be repaired by a method called posting. Not all cracks can be repaired so it's best to get the machine shop to inspect and magneflux the ports. Most cracks will be in the exhaust seats. Have the machine shop check the valve guides also. It's hard to get a feel for how good the valve guides are until the head has been cleaned.

2) Machine shop tasks, first round.

When the head has been disassembled I take it to the shop for the following task's to be performed. I get the cam bearings removed and the head hot tanked or cleaned. The guides are checked and the seats magnefluxed. If guides are necessary they are replaced at this time. The exhaust seats are then cut and seats for the oversize exhaust valves are installed. The intake and exhaust seats are then roughed in for a 3-angle valve job. Also get the intake manifolds degreased.

3) Porting

When I pick up the head and manifolds they are ready for porting. As I mentioned earlier I lay out the cylinder diameter and scribe the combustion chambers. If there is not an bare block available to scribe the cylinder diameter a head gasket can be used but keep in mind the diameter of the fire ring on the gasket is larger than the cylinder diameter. The lines you scribe will have to be adjusted to provide for the proper reference lines.

The exhaust ports can be layed out and either worked by hand or on a mill. If you have no access to a mill the job can be farmed out. I did two heads including set up and cleaning the work area in an hour.

Working the short side radius is the biggest problem. Its hard to get it nice and round. I rough it in as good as possible using the die grinder and then smooth it using what I call the shoeshine method using the emery cloth from the shop roll. I tear the emery cloth into a strip about 24" long and 1/4" wide. The strip is then placed through the port and drawn back and forth in a manner similar to shining a shoe. Any ridges can easily be smoothed down.

When the intake and exhaust ports are done the templates can be made and the port pattern transferred to the manifolds.

4) Machine shop task's, second round.

When all the port work is done the head and valves are returned to the machine shop for the final valve job and cleaning. The seats are cut to the final dimension and the valves are back cut. If an after market cam is used make sure the retainer to valve stem seal clearance is checked. If necessary the end of the guide can be shortened. After the valve work is done the head gasket surface is level cut. If needed the intake and exhaust manifold surfaces can be cut as well. When all machining is complete the head goes back in the hot tank for final cleaning. The head is then ready for assembly.


I hope this has been of benefit to those who would like to do some of the work themselves. If the task seems to large or is to intimidating as a minimum rework the valve bowl area to remove the ridges and sharp edges and then port match the intake to the head and the turbo to the manifold. Even if stock valves are used clean up the valve bowl. I hate to put a number on it, but probably 75% of the advantage of a ported head is due to work in these areas.

Tell the guy at the machine shop what your plans are and most will work with you. If not find a shop that will. I have been doing this for many years and have used several different shops with good results. So be brave and try it!

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