ĦMR.AWESOME!

iTrader: (2)

So basically, scavenging occurs when the exhaust pulse from one cylinder helps to suck out the exhaust of another cylinder, right? This works best with equal-length headers, right? Wouldn't the firing order have to be something like 1-2-3-4-5-6-7-8 so that each pulse is equally set apart from one another? If that's true than it doesn't really apply to our cars. I feel like I'm missing something here. Can someone help me out?

Apeiron

Scavenging is when the exhaust pulse leaves the primary into the larger volume of the collector, causing a negative pressure wave to be reflected up the primary, arriving back at the exhaust valve ideally right at the overlap period while both valves are open, to both pull remaining exhaust gasses out of the cylinder and to pull the intake charge in to more completely fill the cylinder.

ĦMR.AWESOME!

iTrader: (2)

Does the pulse only travel back up the primary from which it came? Or does it only effect the primary from which it came because of the time it takes the pulse to travel? If so, then that's why you would want equal length, so that the scavenging is occuring all at the same rpm, and you get more power there, right? And that's also why the firing order doesn't matter. Is there a way to figure out at what rpm scavenging will be best? Thanks for helping me figure it out, btw.

Apeiron

There are some smaller reflections up other tubes as well. Back in the days when cars were bigger and understanding of them was smaller, you could get "180 degree" tri-T headers with crossover tubes for some applications that would attempt to maximize adjacent-cylinder scavenging with the firing order issues you mention. The effect on performance is small, and the systems were expensive, complicated, and difficult to fit in a car.

ĦMR.AWESOME!

iTrader: (2)

So basically, it's not going to cause a huge difference, and I shouldn't worry about it too much when buying headers.

Apeiron

If you're not designing your own headers, its not something to worry about. You're stuck choosing from a small selection of headers on the market that will fit the platform.