5. Gasket matching is a cheap...
5.Gasket matching is a cheap and easy way to get more airflow. The scribed circle in the picture was made by placing the gasket on the head and tracing it. All that's left to do is grind away till we hit the lines.
Important TermsCCing:The volume of the combustion chamber of the head has a direct effect on compression ratios. A smaller-than-stock CC volume will increase the compression ratio (CR), while a larger combustion chamber will decrease the CR. Because of this, it is important that all the combustion chambers are the same size, or each cylinder will have a different compression ratio and cause tuning problems later. CCing is performed by filling each combustion chamber with water or another liquid. The amount of liquid it takes to fill up each combustion chamber tells us the volume of each chamber. Material is then removed or added from individual chambers until they are all equal.
Intake Manifold Gasket Matching:As they come from the factory, the ports on most intake manifolds don't line up perfectly with the ports on the head. This is because of loose manufacturing tolerances to keep machining and tooling costs low. As a result, there is often a lip or bump where the head and manifold meet, causing a significant restriction and reduction in airflow. Gasket matching removes this restriction and can increase power-all for free! All you have to do is place the gasket on the head, then bust out the Dremel and hog out the ports until they perfectly match the gasket. Repeat on the intake manifold and, viola, you're done!
6. A must-have for any serious...
6.A must-have for any serious cylinder head shop, the trusty flow bench measures how much air (cfm) actually flows through the head-before and after the headwork.
Flow Bench:Without this device, porting would be a strictly hit-and-miss deal. A flow bench measures airflow though cylinder heads. The bench lets head porters see if the changes they made to the head actually improved airflow before they actually bolt it to an engine. In addition, it gives quantifiable numbers that can be compared to the numbers from other heads on other flow benches. This is a must-have for any serious head shop.
Aftermarket Valves:While multi-angle valve jobs can improve airflow, if you want even more airflow, it's probably time to look at bigger and better valves. Obviously, bigger valves can flow more, but that's not the only benefit. High performance and particularly turbocharged engines can see very high exhaust gas temperatures (EGT). Valves made of stainless steel and those that are filled with sodium can withstand higher temps that OEM valves, making them a wise investment that can not only increase power, it can help with engine longevity too.
7.A beautifully sculpted intake...
7.A beautifully sculpted intake port. This porting was done by a computerized CNC mill.
Unshrouding:Unshrouding is the removal of the excess material on the head immediately around the valves. Ideally, there should be at least 1/3-inch around the valve and the cylinder head at full lift. If there isn't, airflow will be impeded as it flows past the valve and hits the wall of the head, impeding flow. By clearing a space for the air to transition smoothly past the valve in a tulip-shape funnel into the engine without running into a restriction, more power can be made. Unshrouding clears the path for this tulip-shaped funnel.
Hand Porting:The old-school way of cylinder head porting is also the most common. With "hand-porting" all the grinding and shaping is done by hand with a Dremel-type tool. The porter relies on their eyes and experience to get everything just right.
CNC portingCNC uses a computerized machine to re-shape and smooth the cylinder head. Because a computer controls it, the chances of getting each port and combustion chamber matched perfectly are higher. CNC mills are extremely expensive, which is why most people still do it by hand.
8.Here the valve guide has...
8.Here the valve guide has been ground down to further increase airflow. In picture number 7, the guide was not ground down.
Extrude Honing:A method of porting where material is removed from the head by forcing putty mixed with sand through the ports. This only slightly enlarges the ports while keeping the basic shape and contours the same. The real benefit comes from the cleaning up and smoothing of all the walls in the ports. Things like intake manifolds can also benefit from extrude honing. Good for street and race engines alike.
PolishingPolishing of the combustion chambers and exhaust ports is standard fare for a good porting job. Polishing the combustion chamber can prevent the buildup of carbon and help ward off detonation. Polishing the exhaust ports can also increase airflow. Intake ports are typically not polished. This is because leaving a slightly rough surface on the intake ports can help prevent fuel from sticking to the walls of the head and causing drivability problems. So if your head shop wants to polish your intake side too, you'll have good reason to question their expertise.
9.Here's a view of a head...
9.Here's a view of a head that's received some work. The port on the left is an intake and the one on the left is an exhaust port.
Valve springs/retainers/keepersIf you plan on spinning your engine to higher RPMs than it did from the factory or using bigger camshafts, it's a good idea to upgrade your valvesprings, keepers and retainers if you want it to live a long and fruitful life. Soft OEM valvesprings are oftentimes not up to the chore of holding the valve closed at high RPM and can physically bind if used with a cam that has additional lift (this is extremely bad). Stiffer and specially designed valvesprings can prevent this from happening. This is also a good time to look into things like titanium retainers, which in addition to being stronger, are lighter and can reduce wear on other valvetrain parts (good for performance and longevity). Many people are unaware that every time a valve closes on, it bounces on its seat. As the valve bounces up and down, the valve leaks. So even engines with mild camshafts can often gain power with slightly stiffer valvesprings and lighter retainers.
Intake Manifold SpacerThere are several different types of spacers on the market that sit between the head and the intake manifold. These spacers are made of materials that are supposed to isolate the manifold from the head and reduce the temp of the intake manifold. We've tested these in the past and found intake temp reductions of about 15 percent, on average. In theory, a 15 percent reduction in intake temps should yield a 1.5 percent increase in power.
10.Aftermarket dual valvesprings...
10.Aftermarket dual valvesprings are often overlooked when doing headwork. Custom valve springs are a good thing to look into if you've got your head apart.
QuenchQuench is one of the least understood cylinder head dynamics. Basically, a quench zone in an internal combustion engine is an area where the piston and the head come extremely close (0.05 inch) to each other at top dead center (TDC). The area where the piston and head almost touch is called the quench zone. Quench zones are usually around the perimeter of the head and are designed to force the air/fuel mixture towards the spark plug. Quench zones help reduce preignition and detonation, so it's important not to screw them up. For what it's worth, using oversized head gaskets can make the gap between the piston and head so large that it can negate the benefits of having a quench zone at all-which can bring on detonation despite the overall lowering of the compression ratio that the thicker head gasket would cause. You've been warned.
 11.Titanium retainers are...  11.Titanium retainers are lighter and stronger than OE units. These Skunk2 pieces are a nice example. |  12.Stainless valves come in...  12.Stainless valves come in all different sizes and shapes for virtually any application. If you expect to see high EGTs, look into a set. |  13.Here's a diagram to help...  13.Here's a diagram to help you bring it all together. |