Porting cylinder heads for better performance is as much an art as it is a science. Strange as it may seem, just making the intake and exhaust passages bigger will not always improve performance, and may actually hurt it. The expert port polishers are still guys with a lifetime of experience and the ability to visualize the invisible gas flow at high speed in 3D. They are like wizards. But there are certain easily done basic techniques that even a beginner can learn and that work on all engines. Doing just the basic gasket matching, port smoothing and bowl blending it is not unusual to see 10% power increases across the board.
First things first, you need the proper safety gear. Porting and polishing involves grinding away metal and as such there will be grit, grindings and dust flying once you spin up the tools. Safety googles and a dust mask are a minimum; you may want a full face shield. Gloves are also a good idea, not only to keep your hands clean, but to keep from grinding off any fingerprints. Be extra careful around loose fitting clothing, jewelry and long hair; tuck it in, remove it, or tie it back before you start.
There are not a lot of tools needed to do your first porting and polishing job. You will need an electric or air powered high speed die grinder, some abrasive rolls and the mandrels they mount to, all of which are included in the Eastwood Engine Porting Kit with Die Grinder. Also available in a mini die grinder kit, or with just the rolls and mandrels. You may also want some carbide burrs, which are especially helpful if you are working with cast iron. If you are working with aluminum or other soft metals you may want a tube of Eastwood Grinder’s Grease too, to help keep the tools from loading up with metal.
The Three Basics
Gasket Matching – Gasket matching is the process of matching the size of the port to the size of the intake gasket. Often times there is an overlap where the intake manifold runner is slightly bigger than the opening it mates to in the cylinder head. By tracing the opening of the gasket on the mating surface of both head and manifold you can be certain the flowing gas has a smooth transition between the two. It is not important to open them up bigger, the important thing is that there is no step that disrupts the flow.
Port Smoothing – Here in the 21st century cylinder heads come direct from the foundry with ports much smooth then was imaginable back in the 1950s when most classic power plants were being cast. On top of improved casting techniques, the design of the ports is much better too. But most old school cylinder heads have rough cast ports that can be much improved with a little work. Firstly, you want to grind out any shark, jagged, left over casting flash in the ports. Secondly, you want to smooth any sharp transitions or obstructions in the port. And lastly, you want to generally smooth the port walls. Be careful on the intake as a slightly rougher wall helps fuel atomization. Above all remove as little metal as possible.
Bowl Blending – Blending the surfaces of the combustion chamber, or bowl, has 2 benefits. One, eliminating sharp edges helps stop pre-ignition from localized hot spots. Two, unshrouding the valve lets the mixture flow better into and out of the combustion chamber. It’s a good idea when working in this area to insert an old set of valves so you can avoid grinding too close to the seats. Remember, making the chambers bigger will decrease the static compression ratio, so again, take out just as much metal as you need too. Never use a carbide burr in the combustion chamber, they are much too aggressive and will remove too much metal.
- Take a good new intake gasket and attach it to the head loosely with a couple of bolts.
- Scribe a line around the ports, using the gasket as a template. A carbide scribe of finishing nail works great, you can also use a Sharpie but you will quickly rub off the ink.
- Depending on how much material you need to remove, start grinding away with the carbide burr or an abrasive roll. Don’t grind in any one area too much. Instead work around and around the port removing a little bit at a time until you have opened it up to your scribed line. Later you can use the same technique on the intake manifold ports too.
- Once the ports are opened up properly, continue to grind and smooth your way toward the valve seat. For the sake of durability and good sealing try to stop your grinding 1/2 inch before the actual valve seat.
- Feel and look inside the port to find any flash and rough jagged edges left from the casting process. You may want to attack these with a carbide burr first to speed things along. Grind these smooth.
- Then work the cylindrical and tapered drums around and in and out of the port until it is a uniform smoothness throughout.
- Flip the heads over and work the area under the valve seat. There is usually a sharp ridge in the port in this area that should be smoothed into a more gradual transition. Again, be extra careful not to cut into the valve seat itself, or weaken that area.
- A particularly important area of the intake port to smooth is the short side radius. This is the sharp turn the port has to take as it changes direction just before the valve seat. In this picture it is below and just ahead of the tapered abrasive roller.
- It’s a good idea to work all the intake ports, then the exhausts, then the chambers. That way you are more likely to get more uniform results. It will also take less time this way, as you will be able to work faster as you practice on each port.
- There is no need to gasket match the exhaust ports to the header or manifold. In fact popular wisdom holds that having a smaller port and a step will help scavenging and limit reversion. Reversion is the exhaust being sucked back into the cylinder during the brief period when the valve is opened and the piston is on its way back down for the intake stroke.
- Smooth the same sorts of casting issues and sharp edges you addressed in the intake as you work the exhaust ports. Unlike the intake, which prefers a rougher finish to promote fuel atomization, the exhaust can be polished to a mirror finish if you want. The smoother the finish inside the exhaust the less likely you are to get carbon build up over time. Eastwood offers abrasive drums in 240 and 320 grit specifically for this.
- Next on to the combustion chambers. The very first thing to do on the chambers is knock off the sharp edge all the way around left from milling the heads. Just take an abrasive roll and make one lap all the way around the edge of the combustion chamber.
- It’s a good idea while blending the combustion chambers to put an old set of valves in to protect the seats from your abrasive tools.
- Smooth and grind and rough casting areas within the combustion chambers. Remember, every added CC of metal you grind away will lessen the compression ratio, so grind away as little as possible (unless a lower CR is one of your goals).
- Depending on what motor you are working with, there may be problem areas in its design that are known to shroud the valves and affect flow. Consult the internet for more specific information about your project.
- After working the combustion chambers it is a good idea to CC them and make sure they are all equal. This is done by putting the valves in and covering each chamber with a flat piece of Plexiglas with a hole in it, sealed to the surface with a little grease. Use a graduated cylinder to measure how much fluid it takes to fill it entirely.
- Repeat porting process on the intake manifold runners and exhaust manifolds (if running OEM style cast iron). Headers do not need any extra attention; tubular headers are typically already smooth inside.
- Clean everything thoroughly inside and out to remove all the metal shavings and abrasive grit before starting to reassemble the motor.
That is all there is to porting cylinder heads. At least, that is all there is to the technique of porting heads. All you need to learn now is the art of exactly what and where to grind away in order to reshape the ports for best flow. That is going to be different for every motor, and even every different cylinder head casting for each motor. For more of the art behind optimal porting Eastwood offers a 160 page book by David Vizard called “How to Port & Flow Test Cylinder Heads”. This book delves deep into flow characteristics and how to improve them. It also shows you how to build a flow bench to test your work in the shop, before the motor goes together.
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