Modding the stock intake manifold (Upper not lower)

[infernosg]

Originally Posted by vex

Turbulent flow=good
Laminar flow=bad

Yes, but this

Originally Posted by vex

Edit: Let me clarify it a little bit: Rough up the surface of the intake runners. The rougher the better. If you smooth out the surface of the runners you create a laminar flow which slows down the flow going to the intake ports. As such you will reduce the airspeed velocity which results in a lower torque curve.

is not correct. Turbulent flow != higher velocity but rather, more energy. Laminar flow is typically considered to be uniaxial whereas turbulent is not, so in the direction of your flowlines laminar flows will always have the greater velocity. Due to its higher energy a turbulent boundary layer is smaller and more stable than a laminar boundary layer so it will adhere to the surface better (think golf balls).

To the OP, smoothing out the transitions is good, but for finish you don't want a mirror finish, nor do you want something resembling sandpaper in there. Too smooth and your flow area will actually decrease (due to large laminar boundary layers) and hurt flow into the engine. Conversely, too coarse will result in excessive friction, which will slow down flow significantly despite utilizing the entire flow area.