Tech Corner: Porting and Polishing Your Own Cylinder Heads

Porting and polishing cylinder heads is something every engine builder knows they should do. However, having the job done by a machine shop can cost a lot of money. Not to mention, you have to take the time to research the best place for the job, so you know that money is well-spent. And speaking of money, porting and polishing cylinder heads can cost hundreds of dollars that you might not have to spend.

So, what about doing it yourself?

Well, let’s explore what that would entail. What exactly is porting and polishing? How is it done? What will you need? Let’s get an introductory look at exactly how you can teach yourself this new skill.

What Tools Do You Need?

Porting and polishing cylinder heads is one of those jobs that is heavily dependent on the tools you have access to.

First, you’ll need a Dremel tool to perform this task, along with the right bits and extensions. Now, the good news is you can purchase Dremel kits that have everything you need to port and polish heads, which is a great way to get yourself started. But keep in mind that these kits generally consist of sandpaper bits. For the port work and for knocking down heavy burs and casting marks, investing in carbide bits and stone bits is going to make your life much easier. (But don’t write off those sandpaper bits just yet—they’ll come in handy later.)

If you are just working with bits, make sure you have 3-inch and 6-inch shanks. Additionally, a whip extension for your Dremel is going to make getting at hard-to-reach areas much easier. (It’s not essential. Though, if you intend on making this a regular process, it’s a worthy investment.)

Also, you’re grinding up metal—so do not forget eye protection, ear protection, and respiratory protection. Safety first, kids.

You’ll also need the proper tools for tearing the head down and reassembling it—namely, a valve spring compressor. Because the head will be disassembled and small fragments of metal can get in the seats and valve guides, you will want a way to clean the heads properly when you are finished. A light oil lubricant like WD-40 should be on hand. It also wouldn’t hurt to lap the valves when you are finished.

Porting Cylinder Heads

Porting is the more intimidating step when tackling this job, as you are working to physically enlarge the ports. It’s actually something many DIY guys leave behind, but it’s really pretty simple. The process starts by securing the intake gasket to the cylinder head and scribing the openings. Then, remove the gasket and gradually open the port up to match the gasket. So long as you gradually taper the port to match the head and don’t try to reshape it, you can’t really damage anything.

What you’re trying to achieve here is matching the port of the intake to the gasket you are using—no larger. Take your time and work gradually around each edge. Because you are removing metal, it’s a good time to break out your carbide bits. Using an arrowhead bit is going to help taper the opening to the rest of the port internally. After the carbide bit is used, go back over your work with a sandpaper or stone bit, so you can smooth out any rough spots or burs that may have been left behind.

One thing many people suggest is that once this step is complete, you should stick with the gasket you are shaping the ports to. I definitely recommend this as well, because any variables may change the seal and flow qualities of the port work.

Also, you won’t want to do this for the exhaust side, just the intake side. Exhaust headers and manifolds often feature ports on the header or manifold that are larger than the head, which creates a step. This step works to create a low pressure area that helps with drawing air out of the cylinders. Port matching can result in the loss of this low pressure area, which can be detrimental to power.

Polishing Cylinder Heads

Polishing is the easy step in this process but is still time-consuming. When cylinder heads are cast, many of them skate through as-is with a rough finish in the ports and some casting marks or burs. Your goal here is to get in and polish these imperfections to a smooth finish. (This is where you’re going to thank yourself for picking up long bits and even a whip attachment for your Dremel tool.)

When you start the polishing procedure, you may still want to keep those carbide bits handy. Start by looking for burs and heavy casting marks, as these are the first things you want to address. Taking the time to knock them down will not only speed up the process but also will save you from having to swap out worn bits.

You want to take your time here and work over these marks gradually. Sandpaper bits and stone bits will be eaten up in this process rather quickly, so having fresh sets to swap through is going to make your life much easier.

You will find that many people like to work around the ports of their cylinder heads in a swirling motion from the outside in toward the valve. This is because the natural wear marks left behind are believed to cause a swirling effect on the air as it moves into the engine. This is favorable to those looking to help better mix the air and fuel before it is delivered to the engine. In either case, you will want to polish every part of the intake all the way up to about half an inch away from the valve seat.

Surface Finish

Now, this brings us back to the level of polish you are trying to achieve. So many people are back and forth on mirror finishes. A good rule of thumb I’ve found, is that a mirror finish is good for direct injection engines while a semi-rough finish is good for carbureted or throttle body injected engines. This is because the rougher finish is good for atomizing the fuel mixture before it reaches the combustion chamber. However, if no fuel is present in the intake side prior to reaching the cylinders, you might as well make the surface as smooth as possible to speed things up.

I also can’t leave out the combustion chamber. You don’t want to reduce material here as you can reduce compression. Though, you still want to smooth out sharp edges and remove any casting marks or burs. These areas can soak up heat and cause pre-ignition of the mixture as the engine runs. The idea of polishing this area is to help air flow from the intake port into the combustion chamber. Because you are working close to the valve seat, you may want to throw junk valves in the head to reduce your chances of damaging the seat. Also, you won’t want to use your carbide bits here, as they are much too aggressive.

There are many techniques out there of blending out and polishing the combustion chamber and we can really dive down another rabbit hole of what works and what doesn’t. But to stay on track, your goal is to just smooth out rough edges here and not remove material.

Why Are We Doing This Again??

Many of you already know why porting and polishing cylinder heads is a favorable trick. So, to save some time, I dropped the meat and potatoes up front. But for those of you who don’t know, porting and polishing your heads is beneficial for power and efficiency of the engine. In a lot of cases, because of the increased CFM of the heads, as much as 30 horsepower is typical with good port work.

Just remember, it doesn’t come for free. This is a slow-moving job—some people will spend up to 20 hours total perfecting their cylinder heads. While you might not be putting in that kind of time investment, you’re still looking at several hours of work. But it’s rewarding work, nonetheless, and you’re left with a valuable skill in your DIY arsenal as well.

Don’t Forget The Intake Manifold

To close, if you want to get the most out of porting and polishing cylinder heads, do not leave out your intake manifold. Before you even go this far, I would have the intake matched to the heads by the machine shop to ensure the perfect match between mating surfaces. Then you follow a very similar process of port matching and polishing the surfaces within. Doing this in combination with polishing the heads is going to get you even more power and efficiency out of your engine.