All Things Being EqualA few months ago, a friend asked me to explain how equal length headers work and why they make more power. I explained scavenging effect and resonance tuning and how you have to decide on a specific powerband to tune for. I went through my half-hour lecture with elaborate gesturing and virtual diagrams in the air that made me resemble something between Bill Nye The Science Guy and an angry gorilla. The end of my momentous speech ended with my friend saying: "So, they just work."
It's been bothering me for quite some time that I wasn't able to fully explain why hey work and I've been losing sleep over it. I needed to put in more thought.
Much to my wonderful girlfriend's chagrin, I have a bad habit of drifting off into deep thought whenever I stand still for more than a few minutes. She says I am daydreaming; I call it a concentrative state of meditative contemplation. Some of my best contemplation is done standing in line-and really, there's no better place to stand in line than Disneyland.
Last weekend, we went on what was a fairly normal day at the park. Tons of people, but the lines weren't that bad. I already had my churro, pineapple float and heard all about the latest politics from my girlfriend's job, so it was time for some quality thinking. Ah, The Haunted Mansion, the perfect line.
You start out in New Orleans Square, with everyone milling around trying to get through the gate. There is always an appropriately dressed mortician ushering people into one of two lines. Everyone thinks one line is faster than the other, but I'm convinced they're the same. We got the left one. They keep the lines alternating so there is always empty space when they switch from one side to the other. This keeps people moving quickly-you see empty space, you want to fill it. By the time you get to the end of your line, the two lines are merging. Timed just right, the first person in the left line directly follows the last person in the right line. Now there is one continuous line moving through the front door.
This seems perfect, so why does everyone hear stories about waiting for an hour to get into a Doom Buggy? Well, the length of the line is fixed, it only works perfectly for a certain volume of people. If there are too many people, they get backed up into two separate lines and things slow down. If there are not enough people, then you don't have a steady stream and lines end up running into each other at the merge point, or there is no real sense of urgency and people end up slowing down or stopping in the middle of the line to wait for friends, take pictures, whatever.
This really is an exact science, one that Disneyland has been working on for over 50 years. At some point, they had to decide on a certain line length, based on how many people they thought would be the peak amount, and how fast they walked through.
It was just a wonderful coincidence that I just happened to be there on a day when everything worked perfectly. I was able to walk onto the ride without having to slow down. It really didn't give me much time for contemplation, but I did find the perfect way to explain how equal length headers work, for the next time someone asks.
This is, of course, a gross simplification of how headers work. However, it expresses the theory perfectly. Individual header tubes need to be sized so that one exhaust pulse is just leaving as the next one enters. At the collector, you want a pulse from one tube to immediately follow the one before it. Just like the line at Disneyland, this keeps everything flowing at maximum efficiency. It's pretty amazing when you look around and find examples of physics at work in everyday life.