How Air "Works"

[Whizbang]

INDUCTION (charge) PIPING

Welcome to my next section where i attempt to get you to understand what makes a "good" design and a "bad" design in regards to piping. Before we continue, i have to explain "mass flow" that was shown above. You need to understand what is happening in the formula to see why air behaves like it does in certain situations.

recall that: Mass Flow = (Density x Velocity x Area) [ M = DVA ]

So that means Mass Flow (M) is proportional to Density (D), Velocity (V) and the Area (A). Plainly, if you increase either D,V, or A, you will increase M. If one decreases, M will decrease. If they all change randomly, then it just depends on it multiplies out. Now also take into account the "Conservation of Mass" meaning that M[sub]1[/sub] going in will EQUAL M[sub]2[/sub] going out unless something is destroying the mass or its being diverted somewhere else. If you get this, then feel free to move on. If not, google.

There are some key ideas that you should follow when designing your charge pipes and for that matter, your entire induction track (head, charge pipes, throttle body, etc). These are as follows:

1.) Use the least number of bends at possible.

Why is this important? Air is a gas. Gases are kinetic, IE move around a lot on an atomic scale. This means they create more friction that say, water would. So when the air is moving through a bend, more friction is created than the straight section. This will slow the velocity of the air. So if the velocity does down and the density and area are the the same, then the mass flow would also have to go down. But the mass flow can not go down. So if the area can't change, then only the density of the air can.

D = P / RT

If you look again at the density formula you'll see that the pressure would have to decrease or the temperature increase, in order for the density to decrease. R is again a constant. Usually it is a combination of Pressure loss and Temp gain.



2.) Limit the change in diameter of the pipe as best as possible

The air will only flow as well as the smallest area in the pathway. So if you have a small throttle body and large charge pipes, it is no better and sometimes even worse than having smaller charge pipes. Even if you increase the throttle body size, the port runners of the intake manifold can present a problem. The reason why this happens is because of a few factors.

A.The Mass Flow rate is reduced. As stated, if the pressure and density are the same, but the area decreases, then the mass flow will decrease.

B. The areas where the diameter increases and decreases generates more friction and was i have previously noted, that isn't good. This will ALSO cause a decrease in mass flow rate due to the pressure loss resulting from the reduced velocity.


There are other factors that make up a "good" design such as overall length of the piping, but that is more for reasons of lag time, etc and is not the focus of this article.