While it is very common to port match an intake manifold to a set of cylinder heads to ensure that there is proper port alignment so that the air /fuel mixture can enter the intake side of the head without restriction, much less has been discussed about the flow of exhaust out of the head and into the exhaust headers. The difference between a vehicle that runs well, versus one that runs circles around similar vehicles, often comes down to the details and the level of attention that the enthusiast applies toward maximizing performance and efficiency. This particularly applies to the exhaust side of the performance equation. A high-flow exhaust system starts at the exit of the cylinder head, and port-matching a set of headers is highly recommended to maximize performance.
Never assume that a set of headers will align properly with the cylinder head of your choice. Unless the header manufacturer is using header flanges that have been cut on a CNC or water-jet machine, be wary of the port alignment. The majority of header flanges are die-stamped out of mild steel. As the die accumulates more stamping time, the header flange will begin to lose precision. The same manufacturer's part number may have perfect alignment at the beginning of its life cycle and poor alignment by the time the die is replaced.
Steve DuSold of DuSold Enterprises states, "Port matching of exhaust manifolds and headers is an old racer's trick and should be the first thing done before other exhaust components are installed. Any material on the header that restricts the flow of exhaust from the head will have a detrimental effect on torque and horsepower output. It doesn't matter if the headers are very expensive 'premium' brands or less expensive alternatives, each header should be checked against a cylinder-head template and repaired according to the port-mismatches found, to maximize performance. To ensure a leak-free fit and optimize the flow of exhaust out of the head and into the header, the header must have port openings that are larger than the cylinder-head port; don't port match a cylinder head to an exhaust-manifold gasket."
Header-port matching can be...
Header-port matching can be done with the cylinder heads installed on the engine or on a work-bench. The passenger side header from a set of "premium" long-tubes for a '73-77 A-body with D-port heads is being removed from the engine bay to allow access to the head ports.
Follow along as we show you how to create a cylinder-head exhaust-port template, and then perform the most common port-matching repair procedures on headers. Depending on your level of skill and access to tools, you can follow the steps outlined and have peace of mind that you've eliminated an exhaust restriction.
Tools & Supplies
Grinding tools
Header bolts
Marking pen
Razor blade/scissors/hole punch
Poster board
Welding and brazing torch
Welding and brazing rods
3/8-inch bolts with flat washers and nuts
Header And Header-Port Matching Tips
Always verify that the template you created for a single head lines up properly with the opposing side's cylinder head before beginning repairs on the "other" header.
Before brazing or welding can begin, the area to be repaired has to be free of any surface contaminants.
An MAPP gas torch can be used to braze, but use a 1/16-inch pre-fluxed brass rod, since the MAPP gas is cooler than a traditional oxygen/acetylene torch.
A MIG welder with 0.025-0.035 wire is the fastest and easiest way to weld a bead around the header tube-to-flange junction. A 110-volt MIG welder will work on 5/16-inch flanges, while a 220-volt welder may be required for thicker 3/8-inch flanges.
An oxygen propylene (propane) torch kit is capable of welding around the header tube-to-flange junction, but much like the 110-volt MIG welder, thicker 3/8-inch header flanges may pose a problem.
Welding and brazing brass are skills that are developed over time with practice. For beginners, practice on expendable parts.
For frequent header-port matching repairs, strongly consider using a junk cylinder head and having a machine shop slice off approximately 1 inch from the exhaust side. Paint or powdercoat the head slice white to allow a good contrast to the exhaust header that you are working on.
Supplies to create a cylinder-head...
Supplies to create a cylinder-head exhaust-port template are minimal and include poster board, a marker, a razor blade (hole punch optional), and a header gasket.
A header gasket is placed...
A header gasket is placed on the poster board and the gasket outline and bolt-holes are traced with a marking pen. A line is then drawn across the poster board and cut down to 4-inches in width.
The bolt holes are then cut...
The bolt holes are then cut out with a razor blade and the mounting hardware is readied. A total of six 2-inch long 3/8-inch bolts, flat washers, and nuts are all that is necessary for installation (four shown).
Next, the poster board is...
Next, the poster board is taken to the cylinder head and the template's bolt holes are lined up. A 2-inch bolt is then threaded in the front cylinder's exhaust bolt hole, the flat washer is slid over it, and the nut is threaded on, so that the poster board is just tight enough against the head to allow proper alignment of the other bolts.
The remaining bolts are installed...
The remaining bolts are installed from front to rear through the template as previously described. After the template is affixed, the nuts are tightened so that the poster board is flat against the exhaust ports.
The outline of the head ports...
The outline of the head ports is traced by using a pencil or by applying pressure with a finger to leave an impression of the exhaust ports in the poster board.