When your looking to gain a little more power out of a naturally aspirated engine the most important area to work on is cylinder head porting and polishing. Why? An engine is also thought of as an air pump, it takes in an air/fuel mixture, compresses and explodes it and expells the waste out the exhaust, in other words, getting the engine to pump more air by increasing the air-flow through the cylinder heads.
Cylinder head porting and polishing will improve the performance of production cylinder heads by removing the flaws that come from mass production but will not correct any design or engineering problems. If you're going to perform some basic cylinder head porting yourself start on a junk cylinder head,get the feel of things first and then move on to your heads. The other thing to note, is that this job requires some rather basic tools. You'll need a high-speed pneumatic die-grinder,carbide cutters, and a high-pressure air compressor to power the grinder.You'll also need a variety of sanding rolls and flap wheels.There are many companies you can buy these from but Standard Abrasives is very popular, they have a wide selection of porting tools and kits available.
Fortunately, there are a number of things that you can do to improve air-flow, particularly through the cylinder head. The first is to ensure that nothing obstructs or restricts the air flow to and through the cylinder head, from the moment air enters the intake system until the moment it exits out the exhaust. However, certain obstructions in the cylinder head ports, such as the valve stem and the valve guide boss, cannot be eliminated completely but can be minimized by narrowing the valve guide boss. Your main objective here is not remove to much material but to remove the restrictions and shape and blend the port so that the air has a nice smooth path into the cylinder.Some basic measuring tools could be handy here to check your work. Use an inside caliper to make sure all the ports are the same size.
When you have finished removing the restrictions and shaping the ports it's time to smooth them down with a sanding roll, no need for a smooth finish on the intake ports a 40 to 80 grit finish will do.The exhaust ports and bowls can be smoothed down and gone over with a flap wheel.
This project is has six basic steps
1. Intake port entry enlargement, surface finish and port match
2. Smooth the intake short side radius,valve guide bosses and pockets
3. Smooth the exhaust short side radius ,valve guide bosses and bowls
4. Exhaust port and bowl polishing
5. Intake manifold port matching
6. Combustion chamber polishing
Combustion chamber polishing will help reduce carbon buildup
Be very careful and try not to touch any of the valve seats with the tool when grinding and polishing.
When polishing the combustion chambers you can insert an old intake and exhaust valve to protect the seats .
When you are finished with your port job it is a good idea to send your heads to an automotive machine shop and have them grind the valve seats and valves and also any other machining that may need to be done, valve guides, surfacing etc.The rule here is that poor valve seats produce poor results almost regardless of how good the port might otherwise be. A good valve job is an important part of good performance so don't skimp here.
For more information and ideas on cylinder head porting and polishing
visit http://www.squidoo.com/How-To-Port-Cylinder-Heads
