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.
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.
Check out the Eastwood Blog and How-To Center for more Tips and Tricks to help you with all your automotive projects. If you have a recommendation for future articles or have a project you want explained don’t hesitate to leave a comment.