Tech: Port It Yourself - Cylinder Heads
Tips and tricks for porting your first set of LS cylinder heads
From the February, 2013 issue of GM High-Tech Performance
By Justin Cesler
Photography by The Author
Porting cylinder heads has long been a right of passage for serious hot rodders looking to add power on a modest budget. Armed with the right knowledge, the correct tools, and a couple of nights in the garage, it’s an easy and almost free way to pick up airflow, which results in increased power and decreased e.t.’s at the track. However, with the wrong knowledge, or an overzealous hand, home porting of cylinder heads can literally ruin a set of castings, taking them from a quality off the shelf piece to a set of paperweights in less than a minute. And because of this, it’s pretty difficult to find anyone out there willing to show the ins and outs of a hand-porting job, since it’s easy to put the wrong info into the wrong hands. Well, that, and the fact that cylinder head porting is more akin to a witches’ brew of knowledge and experience than a straightforward bolt-on modification. But that doesn’t mean there isn’t hope for the budding enthusiast looking to modify a pair of heads in their free time and try them out on the engine of their choice.
 Gabe chose to start with...
 Gabe chose to start with a set of “317” castings, which were originally designed for GM’s 6.0-liter truck engine family (LQ4/LQ9). With large 71cc combustion chambers, and 2.00-inch intake and 1.55-inch exhaust valves, the 317s are a good choice for boosted LS applications, as they offer large 210cc intake runners and a substantial drop in compression over a factory LS1 cylinder head.
 The 317 ports are very...
 The 317 ports are very similar to those found on the LS6 cylinder head, with virtually identical specs on both the intake and exhaust side. Here is a look at the stock cathedral intake port, which measures in at 210cc and flows well into the mid-200 cfm range at .600-inches of lift in stock form.
 The exhaust runner on...
 The exhaust runner on the 317 casting can be opened up substantially, and can be matched to your exhaust gasket for maximum flow. But be careful, you don’t want to just go all out here and remove everything, it’s critical to retain the “short turn” (the bottom of the port), along with material near the bore wall, which is where the majority of the flow gains come from.
 Cylinder head porting...
 Cylinder head porting is much more about knowledge than it is about tooling, but every cylinder head porter worth a damn will have some well worn tools that they can’t live without. Gabe Darveau uses two different die grinders, the larger of which takes care of heavy cutting, while the smaller die grinder is used for finishing work and getting into the smaller areas.
 Gabe uses a plethora of...
 Gabe uses a plethora of aluminum carbide burrs to complete the porting job, with each burr being used for a specific purpose. While you may not need every burr shown here, you will need at least a fast cutting radius end cone, a big and small cylindrical burr, and a ball-end burr for getting into the tight areas.
 Working a cylinder head...
 Working a cylinder head by hand has many advantages, but it takes a sharp eye and a serious attention to detail to get each port similar to one another. Using red brush-on layout dye, Gabe marks around each port (intake and exhaust), allowing the dye to dry before making his scribe marks.
 Beginning with the intake...
 Beginning with the intake side of the cylinder head, Gabe scribes a new intake port opening that features a 2-degree tilt, which helps the intake’s “short side bias.” Note that we’re not looking to open up the actual intake port opening very much (if at all), we’re just trying to gently correct the air path going in before working on the actual runner.
 Looking into the intake...
 Looking into the intake port, you will notice a rather large obstruction along the right side wall, up near the top of the cathedral area. This bulbous obstruction is actually a casting boss for the rocker arm stud and can be removed completely during porting. The rocker arm stud will need a little thread sealer, but this shouldn’t leak any air once the stud is installed.
 With the rocker arm boss...
 With the rocker arm boss removed, Gabe began moving further down the intake port, working the area around the valve stem guide and along the short and long turn of the port. Notice how much straighter the right side wall of the runner becomes after grinding, while almost no porting is needed along the bottom portion of the casting.
This month, we’ve teamed up with Gabe Darveau, of Vengeance Racing, to go behind the scenes of a cylinder head porting job. Gabe’s been doing this type of work on LS cylinder heads for years and has been taught by some of the very best at the School of Automotive Machinists, where he honed his skills before heading out into the performance aftermarket. What Gabe shared with us was a meticulous approach to cylinder head porting backed by science and experience, both of which we can learn from and apply to our at-home projects. If this is going to be your first time jumping into a set of ports, we recommend you get a spare set of cheap castings and think of them as an experiment; cylinder head porting is tricky and you can “find air” on a set if you go too far…so take your time, do your research, and think before you grind. If you’ve been around the game for a long time, feel free to combine these tricks with your existing knowledge to tweak just a little more out of your hand ports, as there is practically never enough to learn about the world of airflow as it pertains to an engine combination.
 Looking at the intake...
 Looking at the intake runner from the combustion chamber, you can get a good view of the modifications done around the valve guide area. You want the valve guide to be narrow, with a blunt front side and a long sharp backside tail to keep the intake air moving quickly and with minimal disturbance. If you can picture an airplane wing, that’s the shape you’re looking for here.
 Gasket matching the exhaust...
 Gasket matching the exhaust port is the first step in the process and is mainly done by going upwards and outwards. Pay attention when working around the “short turn” section of the port (the lower floor of the port wall), as you want to keep this area intact. In fact, many aftermarket castings raise this upwards for maximum performance, but that’s not something a home porter can easily accomplish, so we’ll just leave it alone for the time being.
 With the port exit opened...
 With the port exit opened up to the gasket scribe line, Gabe began to work on the interior of the port, using similar techniques to those shown on the intake side. Again, you want to narrow the valve guide area while maintaining the proper shape, and smooth the transitions in front of and behind the guide for proper flow.
 Using a set of oversized...
 Using a set of oversized valves, Gabe began to work the combustion chamber. You have two goals here, the first of which is to slightly unshroud the valves, the second of which is to polish the chamber and clean up the area around the spark plug boss. Make sure you are careful around the valve seats; you don’t want to blend too far.
 Finally, it was time...
 Finally, it was time for Gabe to break out the sanding and polishing grits to smooth out the intake, exhaust, and combustion chambers. The ports don’t need to have a mirror finish, so just take care to get them smooth with some texture left in them. After this, you’ve only got 7 sets left…so break out the jams, get comfortable, and keep working!
241 Castleberry Industrial Drive, Suite B