Thanks gentlemen, helps a bunch and yes that is the area I was referring to and your logic is understood.
Seems like ideally one would want a port cross section (size and shape) to be equal to the intake runner feeding it as much as possible and for as long as possible, not just matching at the intersection. Then deal with the turn radius and bowl to minimize turbulence in the valve area as obviously this is generally where all hell breaks loose.
Almost seems like from an intuitive perspective, for what that's worth, one would want to optimize the far side and sides of the bowl to enable a nice flow on that surface as it is getting blasted from general flow direction while optimizing the floor and short turn radius to shear as little as possible and not interfere with the rest of the flow. Short side work is to minimize it's negative impact on long side, top, etc..
Is that how you guys see it in concept? I won't belabor this discussion any longer, I appreciate your time.
Thank you.
There is a velocity "profile" through the entire intake tract. It starts at the runner entry in the plenum. First critical target airspeed in my program. This is the slowest airspeed that we see in the tract. We want to accelerate the airspeed from there. We do that by gradually reducing the cross section. We are working with a fixed airflow or "demand" for purposes of this discussion based on engine displacement and what rpm you want to make peak power. As we reduce the cross section, there is a critical area where we want a maximum velocity in the port. There is a specific velocity that I target at this point. Depending on architecture and some other variables, this can either be somewhere int the port upstream from the short turn (known as a minimum cross section area), or it can be at the valve itself. Most of the time the upstream minimum cross section will make more power. From there, we begin to
reduce the velocity for several reasons. One, we want to slow the air down a bit to help get around the short turn, and two, as velocity decreases, pressure increases and in simple terms, that additional pressure helps with cylinder filling. The third velocity "check point" I work with is the valve throat. This is sized for another specific velocity value.
Where the intake manifold and cylinder head come together is arbitrary. When you start looking at the entire intake tract, from entry in the plenum to the valve job, it helps visualize what I'm talking about. This is all based on math.
When you start probing a port with a velocity probe to find where the air really is, you learn a few things. Most of the air (airspeed) is on the floor of the port. It is not equal through the port by any means. There can be 200fps variance in airspeed through any given section of the port. There are dead areas. The roof and back of the bowl don't play much into how well a port flows. A lot of air does flow over the top of the short turn and to the back of the bowl. We also have a valve influencing a lot of this. Ideally you would like even air/fuel distribution 360* around the valve and though the port, but that never happens. Again, architecture dictates a lot of what the air does in a port and we have only so much influence within a given architecture. Even the most advanced, highly developed ports are a compromise between efficiency and packaging.
