![]() This is a very detailed technical article so feel free to bookmark and share. What is a phaser?, What does it do? I get into the details of how the 5.4L's variable cam timing system works. Many are confused about the rattling sounds they hear on light acceleration and many people have been told it is the phasers. But at higher engine speeds these conditions are minimized due to the slight lag time it takes to get the intake charge moving into the cylinder.The Ford 5.4L Triton 3 valve engine is a wonderful masterpiece that many hate and do not understand. It also causes the loss of low rpm power and economy that larger cams experience. This is why a longer-duration camshaft produces power higher in the rpm range. Higher engine speed causes greater exhaust-gas velocity, which relates to greater momentum of the exiting exhaust gases. This effect on performance is directly linked to engine rpm. Smaller amounts of overlap produce a smoother idle, and a slight benefit in top end horsepower. Too little overlap causes the lack of complete expulsion of the exhaust gases, and less intake charge filling the cylinder. More is not always better, as too large of a lobe center angle can result in too little overlap to make good power. ![]() The intake valve on the other hand, opens before top dead center, and uses the momentum of the exiting exhaust gas to start pulling the intake charge into the cylinder. This helps keep the momentum of the exiting exhaust gases to maximize the amount of exhaust gas pulled out (scavenged) from the cylinder. When an engine is running, the exhaust valve needs to stay open slightly after the piston passes top dead center. Increasing lift duration and/or decreasing lobe separation increases overlap. This "overlap" occurs at the end of the exhaust stroke and at the beginning of the intake stroke. This is also known as Lobe Center Angle, and is the crankshaft degrees that are measured when the intake and exhaust valves are both open. ![]() Just to give you an example of cam timing theory, a cam with 107 degrees of intake-lobe centerline will actually be centered at 103 degrees ATDC when the camshaft is installed four degrees advanced. We know that advancing or retarding the camshaft's timing moves the engine's torque band on the rpm scale by moving the valve events farther ahead or behind the movement of the piston, but how much, and in what direction? As car guys, we all like to think that we are expert engine builders and tuners, and a lot of enthusiasts will experiment with advancing or retarding a camshaft from "straight up" (zero) and see what timing position works best for their application. We wanted to know-and verify-what really happens when we install a camshaft at "zero" (straight up), and then simply advance it four degrees. You could spend hours on the computer reading and learning about how a camshaft works, and what the terms like lift, duration, and valve events are, but we wanted do a simple test in regards to camshaft timing. What this means is that we want to keep the intake valve open as long as possible, but as you can figure out, keeping it open too long has a detrimental effect on power. But, if we leave the intake valve open just a fraction of a second longer, the momentum of that fast moving air/fuel mixture continues to force more of the mixture into the cylinder (scavenging effect) as the piston starts its compression stroke (return to top of cylinder). If we close the valve immediately after the piston finishes its downward motion, that incoming airflow abruptly stops. When the piston reaches the bottom of its intake stroke, the air/fuel is being pulled into the cylinder at a high velocity (speed). Basically, when the intake valve opens and the piston starts downward on its intake stroke, the air/fuel mixture developed in the intake is pulled into each cylinder. To keep things running smoothly, there is a direct relationship between the shape of the cam lobes and the way the engine performs at different speeds. As the camshaft spins, the lobes open and close the intake and exhaust valves in correlation with the motion of the piston. But it isn't really that hard to understand. When it comes to camshafts, and the timing thereof, a lot of guys feel that understanding it is a black magic.
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