Gasoline engines burn a mixture of fuel and air. In order to create horsepower, your engine must maintain a good quantity and velocity of air/fuel charge into the combustion chamber. Think of the engine as an air pump. The more efficient your engine can pump air into and just as quickly out through the tailpipe, the more horsepower can be created. To get that, aftermarket components such as quality cylinder heads and high flow exhausts aid for better breathing and improved performance.
Porting and polishing an engine's intake manifold is an essential step in optimizing its performance, particularly if it is modified. Ask any reputable head porter and/or engine builder the key ingredient in porting and chances are 9 out of 10 will tell you porting less offers more. For DIY porting amateurs, we recommend port matching. This means only openings at the end of the runners on the intake manifold do not match up to the port openings on the cylinder head. The resulting mismatch causes congestion of the air/fuel mixture as it travels toward the intake valve, which slows down the velocity of the airflow.
The main focus is to not make the port shaped like a balloon. The bulge slows the airflow (the cross-section becomes larger), and this causes the airflow to "stack up" behind the slowed flow and cause turbulence, which is harmful to good flow. With a little planning, the proper tools, and some patience, the average DIYer can clear up this congestion by port matching (gasket match) the intake manifold to enable your engine to breathe easier!
Essential tools for home porting are either an air operated die grinder or an electric die grinder, carbide bits, a long shank, abrasives, sanding/cartridge rolls, and flap wheels, which you can purchase at your local industrial hardware store.
1. Outfit yourself with safety glasses and a breathing mask; flying metal chips can easily penetrate your eye or ingest in your lungs.
2. With the intake manifold removed, use the manifold gasket to determine where and how much to port the manifold. Place the gasket over the surface that mates up to the engine. The material between the edge of the holes on the gasket and the edge of the holes on the manifold is what needs to be removed.
Mark the area to be removed using the gasket as a guide to eliminate the chance of over-porting. Always refer back to using the intake gasket for dimensional purposes; take horizontal and vertical measurements using a caliper to ensure all the ports are dimensionally sound.
3. With your air grinder set at 40 psi, remove the excess material and open up the ports. Move the aluminum carbide bit consistently around the edge of the port, taking care to not remove material that is covered by the gasket itself.
4. Smooth out the edges of the port once the material is removed with 80-grit sanding rolls. Smooth the edges of the opening into the manifold to give the air a smooth, progressive passage. Inspect the insides of the intake tracts for casting marks and rough areas.
5. Remove the casting marks and smooth out the bends where the manifold changes direction before using the flapper wheels.
6. Polish the inside of the intake manifold with increasingly finer polishing cones. Finish the polishing with a 120- to 180-grit flap wheel. Notice the advantages of using a longer shank to get deeper into the manifold. Periodically remove your glove and run a finger up the runner to ensure you have no waves in the wall surfaces. As with any engine modification, we recommend an experienced mechanic or machinist to properly port your parts.