An engine is essentially an air pump. There are a couple different ways a generic engine can do this, but in 1876 a man German named Nikolaus August Otto (Otto... auto... pun intended?! What a knee slapper!) innovated the first four stroke engine. Even today, most things from an Escalade to a Harley have this four stroke design as its base foundation for an engine. It is a hollow block of metal containing a spinning crankshaft with pistons attached to it. As the crankshaft rotates, the pistons move up and down inside of cylinders to pump air in and out. In order, these four strokes are called the intake, compression, power, and exhaust strokes. This process of the four strokes make up a single pistons total vertical travelling cycle, requiring the crankshaft to make two complete revolutions (four 180 degree strokes).
*The stroke of an engine is the combined measurable distance that the throws of the crankshafts move up and down from the center line of the crankshaft. A bicycle has a crankshaft that you put your feet on to rotate and generate movement though the wheels. It is like measuring your foot from the bottom most distance of travel to your foot at the top most distance of travel while peddling. Each stroke is one movement of a single piston.
Gasoline. Known as a solvent to some people, for most of us it is the primary fuel that powers all of our vehicles. The numbers on the pump aren't just a measurement of how much extra money you can spend by getting the "good gas" when filling up the ole' mini van on your way to yoga. If you think that higher numbers give you more power or better gas mileage, you may be right... but you may be wrong also. Just like everything else in the automotive world, it depends. Keep this in mind: Higher gasoline octane numbers = more resistance to combustion. So why do they provide different octanes at the pump? The answer is simply because of the different compression ratios of different car manufacturers engines. Engines that make high compression provide more performance, but they require higher octane to do it. Compressing gas makes it hot, and given enough compression, it will light itself off before the spark plug does its job. The spark plug will still do its job, creating two flame fronts inside the cylinder that build a high pressure area above the piston and will lead to an uncontrolled high temperature explosion. Because of this thermodynamic science, putting the cheap gas in an engine designed for premium can cause the pistons to actually melt down. Consequently, putting high octane in an engine with low compression will make the engine work harder to ignite the gas which would reduce gas mileage.
*Compression ratio: 1 unit of air when the piston of an engine is at the top of the cylinder compared to the units of air when the piston is at the bottom of the cylinder. An 8:1 compression ratio means that the engine compresses 8 units of air into 1 unit.
*Heads are the top half the engine that seal the cylinders in which the pistons move up and down. They are sized by the amount of space around the valves, referred to as combustion chamber volume measured in cubic centimeters. Bigger chambers provide lower compression while smaller chambers increase compression. They contain passages known as ports in which air flows through. At the ends of these ports there are valves mounted to the combustion chamber which open and close to allow air in and out of the cylinders.
*Mickey Thompson (12/7/1928 - 3/16/1988): A pioneer in the racing and hot rodding industy, he innovated and manufactured automotive parts and competed in the Pikes Peak Hill Climb, Drag, Land Speed, Indy Car, and Baja rally racing just to name a few. His accomplishments are substantial, and his efforts have had a direct impact on the modern world of automobiles as we know it today. He was murdered in 1988. R.I.P. M/T :(
In an effort to improve performance, I cleaned up the cylinder heads using a process called porting and polishing. This involves using a rotary grinding tool to cut, grind, shape, and then polish the airflow passages (ports) to improve airflow. Using a Dremel tool given to me by my father when I was younger, the process took about 9 hours of my time. It's easy to screw up a perfectly good set of heads if you don't know what you're doing. The trick is to not get too greedy removing metal, and keeping the shape of the area near the valves nearly original is important to speed up the airflow through the port openings so that the cylinders can fill and empty easier. This works by way of the venturi effect.
*The venturi effect is process of air speeding up as it goes through a restricted area. It works on the basic principle that there is a pressure differential between each side of the restriction. In an effort to equalize the air pressure, the air must speed up because it can only be separated so much. This is why canyons and mountain summits are typically windy.
In the below picture of the cylinder head, this is the combustion chamber that faces the piston. With the heads disassembled, you can see the large round holes which are the openings to the ports. The small holes are known as valve guides. Normally the valves are installed into the valve guides and slide in and out of the head to open and close off the ports. On the other side of the head are valve springs that pull the valves shut after the cam is done pushing them open.
In this next picture, the left port is shiny and shows all the areas where I have removed metal, whereas the right port is stock and untouched. Cutting the outskirts of the port near the opening is known as bowl blending, the art of smoothing the transition from the port diameter to the valve diameter. Removing too much metal here will ruin the venturi effect of the air flow. Cutting the valve guide bosses and the bottom of the ports into streamlined shapes to open the port up is called pocket porting. I cut the valve guides no problem, but stayed pretty conservative on the rest of the pocket. Impossible to see in the picture, I also trimmed the short side radius of the 90 degree bend into the main channel of the port in order to lessen the sharpness of the corner that the air must flow around. All this work should improve the intake and exhaust flow by at least 20%, which increases the engines volumetric efficiency and allows the engine to make more power with less boost.
The second biggest change to the engine that I looked into was the camshaft. Controlling the air entering and leaving the cylinder is a complex system of valve train components, the important one being the camshaft. As it spins its has egg shaped lobes which will push a valve open, and a spring will pull it closed when the lobe is done passing by. Camshaft design directly effects the power, torque, throttle response, idle quality, and fuel consumption of an engine. The lobes of the camshaft are designed to hold the valve open for a certain amount of time (Duration, which is measured in crankshaft rotational degrees), a certain amount of height (lift), and how fast the lift occurs (ramp rate). The tricky part about the camshaft is that it allows the intake valves and exhaust valves to be open for different duration, lift and ramp rate compared to the exhaust valves. Any time the intake and exhaust valves are open at the same time, it is called valve overlap. Have you ever been next to a Harley at a stop light and its exhaust sounded as if it was hunting and unstable or repeatable? This is due to its valve overlap. The more overlap there is, the more high speed breathing capability the engine will have, but the idle quality will suffer. The center line of the the intake lobe and the exhaust lobe compared to each other creates an important measurement of this overlap called a lobe separation angle (LSA). New engines have variable valve technology which can change this angle depending on load and engine speed conditions, but i'm sure you're lost already so i will not cover it. My engine is obsolete and far from equipped with this technology, and this is enough information, so all is good Charlie!
There is no magic cam, especially for turbo engines. Each one must be custom tailored to its specific engine design and use.
The current cam: Crower brand. 112 LSA. 284/290 degrees advertised duration on the intake and exhaust. Duration at .050" lift is 228/235 degrees. The lift is .479" for the intake and .494" for the exhaust.
Phone calls to different camshaft companies yielded many different results:
- COMP CAMS: "Keep the intake and exhaust duration identical and widen the LSA."
- CROWER CAMS: "Use the same cam you have but maybe try a cam with longer exhaust duration."
- CRANE CAMS: "Use a narrow LSA so that the car isn't lazy while waiting for the turbo to build boost."
- EDELBROCK: "We don't make custom camshafts."
- LUNATI: "Widen the LSA and separate the duration of the intake and exhaust by a few degrees."
Everyone and their grandma's pink Portuguese poodle seemed to have individualistic opinions on what to go with, and at the end it was clear that I was getting offered a bunch of SWAG. Wide LSA, narrow LSA, more duration, split the duration... blah blah blah!!! Arrrrgghhhhh! The problem is that a turbocharged engine is a complex system of many variables, so they are all correct and all incorrect at the same time. Their opinions depend on their frames of reference which have taught them what kind of drivability, performance, and engine characteristics would be "best". There are so many tech experts at each one of these companies. Some build race engines, while some keep it simple. Some are Ford guys, and some Mopar. Calling the same company three times can give you three different answers. I didn't have time to wait for success, so I proceeded ahead without it. My final decision is to see how my current cam sparkles and then evaluate the situation when that bridge needs crossed so that I can create my own SWAG.
*SWAG, a Scientific Wild Ass Guess
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