Porting and Polishing Chevy Heads

The heart of your chevy muscle car engine is the cylinder heads.  A time-honored method for increasing chevy muscle car horsepower and torque has been improving the air flow potential of the engine cylinder heads. There are many ways to do this; expensive "bolt–ons" such as aftermarket heads, supercharging or turbo charging. For the real gearhead with little money and basic mechanical skills, porting and polishing the OEM heads is always an option.
With just a few key modifications, most heads can be made to flow 5 to 10% better than stock and the effort only requires a few basic tools, patience and a weekend’s worth of sweat labor. That’s free horsepower! If you are doing a valve job anyway, especially if upgrading to larger valves, this improvement could be in the 20 to 25% range.

The Basic Steps Are: 

1. Remove ridges from the intake and exhaust port bowls; this is formed when the valve seats are cut and once the heads are disassembled you can easily feel it with your finger; it's in the head just below the seat. Blend the ridge into the port walls using a carbide burr with a ¼ inch die grinder. A variable speed grinder and a light touch are best. Be very careful that the shank of the burr does not come in contact with the valve seat. Remove as little material as possible. The entire port should feature a continuous smooth radius. The valve guide bosses can also be cleaned up but be sure to leave .125 of material surrounding the valve guide hole. You can use abrasive rolls to polish the exhaust ports but do not polish the intake ports.  With the intakes, too smooth and you lose the turbulence needed to thoroughly mix the gas and air being pulled into the combustion chamber.

  

2. Unshroud the valves by gently removing material from the sides of the combustion chambers. Match the head gasket with the bolt and dowel-pin holes in the head and then scribe a cylinder-bore line around the chambers. Using machinist bluing or a dark felt tip marker will make the scribe line easy to see. You then know how far you can safely grind but do not go outside the scribe line or serious sealing problems may result. Again, remove minimal material to avoid reducing the compression ratio. Use some old valves in the chamber to protect the seats while grinding. You can also polish the chambers with abrasive rolls; it will reduce the tendency for carbon buildup.

3. Port match the intake runners to the intake using the intake gasket as a template for a scribe line. Some say this is worth 4% more CFM, 2% is more likely, but every little bit helps.   Do not polish the intake runners or fuel puddling and loss of flow turbulence could result – leave them a little rough.

Tools Needed:
• Variable speed die grinder with 25,000 rpm potential; an air grinder is ok but an electric with variable speed control seems easier to modulate
• Carbide burrs; ½ inch head and some smaller sizes for tight spots all with 2 inch long shanks

• Abrasive rolls (basically medium to fine grits, try to stay below 1/2 inch diameter)
• Leather gloves
• Ear plugs
• Eye protection
• Dust mask
• Duct tape (wrap the grinder tightening nut and tape around the combustion chamber scribe line just in case); running a burr across an unprotected head surface will ruin your whole day – the duct tape offers a little extra protection.

Key Learning: A valve job will be needed after this process because I have never seen anyone port and polish heads without nicking at least a few of the valve seats, no matter how careful they were - so plan accordingly.

Your chevy muscle car can really benefit from this "sweat labor" modification. Do this right and you can feel the added power and torque in the seat of your pants - improves gas mileage too!  The products listed below can help you in your quest for greater performance.

More detailed information can be found at: http://www.chevyhiperformance.com/techarticles/95518_small_block_cylinder_head_porting/