Exhaust flow talk

[Mux213]

Split time it is

Ok scavenging, that was the thing I read about, now I remember!

Okay in my lamemans terms what I remember from it.

You have say 4 cylinders like the hachi, all exhaust ports eventually meet up in the header. If they meet up to quickly or to late the pressure from the exhaust gasses from your first cylinder (which fired a little while back) will hinder the exhaust gasses from the 2nd cylinder (or whichever fires next) to exit which means you loose power, the pressure from the exhaust gasses from the 2nd cylinder then hinder the exhaust gasses from the 3rd, etc.

However if they meet up at the right time the exhaust guesses of that first cylinder have moved so far down the exhaust pipe they have created a vacuum behind them that will help 'pull out' the exhaust gasses from the second cylinder (or whichever fired next), the gasses from the second cylinder then create a vacuum for the third, etc.etc.etc. Increasing the power output. Offcourse there is a certain RPM at which this effect is at an optimum for a certain length at which the header meets up.

This is the whole theory behind equal lenght exhaust headers if I'm not mistaken.

The thing with backpressure was that if you had no backpressure, there was no vaccuum created and you wouldn't have any scavenging effect (or the thing causig the backpressure was the same thing keeping the vaccum intact or sumething like that). But you only needed a little or something because more backpressure means more slowing down of the gasses means less gasses escaping meaning less room for fuel/air mixture meaning less power output.

But again, this is just my lamemans understanding of what I read and I may be repeating it in error.