The Heads
Modern day factory-grade engines often come with twin-cam configuration, which, in other words, translates into a performance and efficiency tuned engine for the car. At first sight, these performance based engines are not hard to spot, but these factory finishes can always be enhanced to give it the firepower it deserves.
When it comes to cylinder heads, terms like “port and polish”, “valve grind”, “valve springs and retainers”, “seals”, “camshaft”, “cam pulleys” and “gasket” are common vocab in the world of performance tuning. Simply put, tuning methods and parts swapping in the cylinder heads department work in a unison manner. There is so much that can be done to give your car its horns and you can’t expect to attain the power you seek with a single upgrade. If you didn’t know already, we here at Pro Tuners will shed some light onto this subject.
HEAD GASKET
A head gasket’s job is to seal the gap between the engine block and engine head. Sandwiched between the block and head, it is a known fact that the head gasket is the weakest link. Though this may sound worrying, rest assured that the factory unit’s head gasket, which is basically layers of paper compressed together, suffices for stock and lightly tuned rides.
However, as you take it up a notch to medium-performance tuning, it is with explosive importance that you take the head gasket seriously as your first line of defense against detonation. A factory head gasket with a good set of strong head studs and appropriate application of torque does the job just fine, sealing the combustion chamber under full noise. Despite this, bear in mind that the risk of it giving way is higher than that of performance head gaskets.
For street machines tuned with high-performance tuning, gasket failure can be catastrophic. In the worst case scenario, the head gasket will pop out as the engine continues to detonate, eventually resulting in bottom-end failure. Think of performance-gaskets as cheap insurance, it may be a pain to replace your gasket but it would be a bigger pain in your bottom-end to change or rebuild your engine’s bottom-end.
There are three types of aftermarket head gaskets: MLS, copper base, and ‘O-ring’ process.
MLS (aka Multi Layer Steel) – Most newer OEMs utilize this kind of gasket. Made from 3 layers of thin steel tightly compressed together, it can be extremely durable for performance-tuned street engines.when correctly installed.
Copper – Used mostly in race engines and high-performance street engines which generate massive horsepower, this type of gasket is more effective than MLS because it doesn’t pop that easily. It requires a very precise mechanical process to install. The delicate process, if not done with perfection, will have the opposite effect, turning your engine into a moving time bomb.
‘O-ringing’ – Known as the groove cut just outside each cylinder either on the block or the head (normally on the head) where an ‘O-ring’ is inserted to provide the copper head gasket with a solid bite to hold it in place, forming a more effective seal.
CAM PULLEY (AKA VERNIER AND CAM TIMING)
This is the most basic aftermarket part that is commonly upgraded by tuners, available from countless local and international brands. When applied to a DOHC setup, it allows drivers to independently advance or retard the inlet and exhaust cam timing to achieve optimum power output and shifting the rev range in which it appears. An SOHC setup, however, has limited room to shift both the inlet and the exhaust timing independently.
PORT AND POLISH
Porting heads are part of a popular performance tuning process. It involves porting the channels of the inlet where air rushes in before combustion. Porting the exhaust channels where hot gas leaves the engine after combustion increases its efficiency. The aim here is to eliminate rough surfaces, restrictions and restrictive angles in the channels of the engine head. The size of the port opening also becomes a factor here.
Port and polish heads can be found in most naturally aspirated performance engines for more power. A force fed engine (Turbocharged/Supercharged), however, sometimes does not really require the port and polish process, though a small amount of port and polish can be beneficial for the head’s efficiency and smoothness.
The whole process is a balancing act between the volume and velocity of air travelling in for combustion and exiting gasses after combustion. A common mistake is making the port too big, causing loss in velocity and torque. Done too small, it will result in restriction and turbulence. The right amount of port and polish needed for your cylinder head to perform at optimal efficiency very much depends on the tuning you have done on the heads, throttle body, inlet manifold and performance camshaft. The flow bench is used by porters to measure airflow through cylinder heads. Reputable head porters will have this machine in their shop to measure the changes they made to the cylinder head to se if it actually improved before bolting the head back to the engine block.
Hand Porting – Relies heavily on the porter’s steady hand and experience in performing a consistent grind while shaping each port/channel to precisely match. This is a cheaper solution if your tuning direction is down the cylinder head works path.
CNC Porting – A computerized machine re-shapes and polishes the cylinder heads. It is more reliable and has a higher consistency in perfect matching when porting and polishing across all ports/channel. It requires expensive machinery so expect CNC porting to cost you some serious dough.
VALVE GRINDS
Referred to as cutting and grinding valve seats which have sharp angles and cast iron imperfections, they can decrease and create travelling air turbulence when entering and exiting the combustion chamber. A valve job or valve angle grinds makes the valve as aerodynamic as possible.
The number of angles refers to the gradient of the valve seat itself. The more angles at which the valve job is performed, the better it will flow. Common numbers of angle grind are typically a 3-angle valve job and 5-angle valve job. However, if cost is a factor, determining number of angles performed, a 5-angle valve job is very costly compared to a 3-angle valve jobs when it comes common DOHC engine heads. Great improvements and efficiency on any cylinder heads can be expected when a common 3-angle valve grind is combined with ported and polished heads.
CAMSHAFTS
Another top priority on the tuning list in the quest for power are camshafts. Performance cams or hot cams can transform the engines response and performance. Since most of people are clueless when it comes to this department, the specs of camshafts are often neglected to the point where aftermarket and second hand units are purchased with disregard of the camshaft’s specs. Fret not though, here are some brief explanations that should help you better understand it.
Duration – The higher the numbers on the camshaft, the more you can to shift the powerband of any engine to the north, increasing its peak power at a higher RPM range at the cost of lower end RPM drivability. Most well known camshaft producers will quote their duration at a 0.050in lift, giving tuners the base in which they can do the comparison. 0.050in refers to the lifting ramp and closing ramp of the camshaft’s lobe. Without the duration number quoted at 0.050in, the figures are useless.
Lift – Measured in inches, it refers to the lift that the valve extends its distance from the head. More direct lift means more horsepower and torque.
Lobe Separation – The separation distance between the centrelines (aka peak points) of the intake and exhaust lobe pair. It dictates how quickly one opens after the other. It is measured in camshaft degree: a lower separations means that the centerlines are closer to each other, hence overlapping. You gain a stronger low to midrange torque, but be prepared to also gain rough idling. A more conservative overlapping is better for idling and a smoother torque curve climb. Force induction and NOS powered engines will benefit from more conservative overlaps as well.
Valve Springs – While this doesn’t increase horsepower or torque directly, it is recommended to include this, especially when you have aggressive camshaft installed. Factory units will give way easily with the added stress from ported and polished cylinder heads couple with hot cams. The tension of the springs varies in different applications and setups. Simple rules apply, the more performance-oriented a camshaft is, the stiffer the valve springs that matches it. A common set of brand new valve springs come with matching valve springs retainer. ‘Long lasting and durable’ are the keywords here.
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