CYLINDER HEAD TECH
The diesel engines of today are quite advanced compared to those first found in farm and commercial equipment from decades ago, with electronically controlled injection events, highpressure injection pumps and variable-geometry turbochargers. It seems federal standards for cleaner emissions is really what drives the OEMS now, but lucky for us bigger horsepower and torque numbers keep coming year after year. While the motors of today have some excellent technology and parts inside them, there is always room for improvement when it comes to absolute peak performance. Just like in the gas engine market, custom cylinder heads are still one of the best ways to find hidden potential within the Duramax, Cummins and Power Stroke engines.
Turning to the crew at Industrial Injection for a little insight on aftermarket cylinder head technology, we can get a little info on just how in-depth diesel cylinder head machining can go. Industrial Injection offers street and competition oriented cylinder heads based on what a particular application needs to attain a specific horsepower goal. There are a few major changes made to improve the cylinder head potential for both stock and modified engines.
Porting of the intake and exhaust runners, performance valves and highrev valve springs are the ones we all expect, but there are other upgrades that can further enhance a head’s durability and potential under the most extreme conditions.
Heads that are cleaned up and pass the crack and pressure tests can start the machining and assembly process. To allow complete access to the intake and exhaust port runners, valve guides and valve seats are removed. Through years of testing flow patterns on a flow bench, master porting dimensions and CNC programs were written to bring the cylinder head to maximum flow potential without sacrificing durability. The cylinder ports’ wall thickness has to be taken into consideration if durability is a concern, as porting too thin can lead to premature failure. This is especially true in a diesel, which experiences such a large heat absorption and temperature change in such short amounts of time.
On a 5-axis CNC machine built specifically for cylinder head porting, state-of-the-art CAD/CAM software runs through each intake and exhaust runner for a lengthy machining process. Angles and smoothness of the bore are done to exacting specifications to ensure proper air distribution to the valve, which will help with overall flow and make for a more useful power band. After the port match work is completed, machine work begins on the valves and other areas of the head. New high-strength, iron-based alloy guides can be installed, which are heat treated for unparalleled durability and wear resistance. The new valve guides also offer a spiral groove on the inside bore that aids in oiling and lubrication of the valve while the engine is operating.
The cylinder head will then get new valve seats made from a nickel-based, non-magnetic material. These valve seats were developed to perform under the most extreme conditions and are extremely resilient to heat stress fractures and cracking. Dropping a valve seat in a brand-new engine is not something you want to be concerned about, and these seats have proven themselves in plenty of engines sold by Industrial Injection. The valve seats receive full multi-angle machining to maximize airflow in and out of the cylinder head.
At this point, the mating surface of the cylinder head can be machined and milled using CBN or diamond tooling depending on the surface finish required by the chosen head gasket. Depending on the application, the cylinder head may also be machined for fire rings, which places a small machined ring groove around each combustion chamber. This is extremely common on both the 12-valve and 24-valve Cummins heads, as fire ring gasket kits have proven to be the most reliable way to seal a cylinder head to the engine block in high-performance and high-boost applications. Some cylinder heads will also have the freeze plug ports drilled and tapped for threaded inserts, which will replace the factory-style pressed-in plugs. Once all the machining has been completed, the cylinder heads will undergo one last wash and the final assembly can be done. New valves and high-rev valve springs with titanium keepers can be installed as well.
This 24v cylinder head is being prepped for installation on a fully built competition 6.7L Cummins short block. Industrial Injection’s competition head includes full CNC porting on the intake and exhaust, new valves, guides, performance valve springs and fire ring head gasket grooves. The factory intake manifold is also machined off, leaving a flat milled surface that is drilled and tapped to accept an aftermarket high-flow manifold.
On the Street Duramax heads, additional machine work is done around the valves. This is referred to as an “unshrouded valve.” Since most diesel engine cylinder heads have the valve face recessed from the deck surface to allow for proper piston clearance, the amount of time the valve is open and the amount of air that can be passed through it is affected. Machining small grooves around the valves gives the air that much more area to travel through before the valve is fully closed. You’ll also notice the groove doesn’t go all the way around the valve, as this portion gets too close to the outer cylinder wall and could cause issues with the head’s sealing surface with the engine block.
Because of the 5-axis CNC machine and CAD/CAM software designed specifically for cylinder head porting, the intake runners on the Duramax cylinder heads are nearly perfect every time. The smooth internal bores and matching profiles eliminate restriction in the air stream’s path and will help with overall engine efficiency. The cylinder head porting should also help increase turbocharger performance, especially when paired with the right camshaft profile that will allow the valves to open and close at the exact moment they are needed to.
This cutaway of a Competition Series 12-valve cylinder head shows the intake runner’s path. If you look at the water jacket pathway on the right, you can see how imperative it is that the porting job be done correctly. If the port work is taken too deep, that dividing wall can become too thin and will be more likely to crack and leak, at which point the head would be unrepairable and needs to be replaced.