jeffy can you explain further? this is the first for me..pressure pulse? 
OK, I guess I'll address this here in general terms so bare with me. Your engine is a air pump. Actually make that four air pumps (#1-4) Each pump turns on (Intake) in the order of 1324. This corresponds to each cylinder in the engine. When ever one pump turns on it creates a high-pressure wave of air. Behind that high-pressure wave is also a low pressure wave. Then the next pump turns on and you get another pulse generated. Basically, you have created a sign wave.
Keep in mind that each time the pump takes in air, it may not be the wave that is initially started on that cycle but one that has already been created. Now here comes the confusing part. The wave goes both ways. The wave will bounce back as it reaches the pump and travel back out to the end then start again traveling towards the pump again.
Timing of the wave will be dependent on the length of the tube. Keep in mind that when the pump starts up the wave that arrives at the pump is already in the channel so to speak. Optimally, you want the wave to arrive at the pump right before. As the pump starts, the wave will push it's way into the pump. This helps crap the pump with the most air possible. Now, if the timing is off, and the high-pressure wave passes the pump the low-pressure wave will arrive at the pump. The air charge entering the pump won't be as strong as it should and performance will drop.
Now that only covers the intake. There is still the exhaust. In simple terms, the same thing happens but in reverse. Here are the differences though; As the pump turns on (exhaust) creates a pulse as the exhaust. So the pulse travels out the exhaust then returns like with the intake. What you want to happen is the pulse to arrive back at the pump right before the pump creates a new pulse. The pulse will then pull any remaining air from the pump.
Theres a lot more but it's a start.
