Intake runner surface

[sierra4000]

Hello,
How way intake runner surface affects flow numbers and power results?
(two same runner volume with different surface)
(rough vs smooth)

Thank You

Radek

 

[sierra4000]

Clarification
if the intake runner is roughened along its entire length,
can I expect any gain?

Thanks

Radek

 

[3DDave]

Changes in section, direction, and surface roughness tend to increase pressure losses due to increased turbulence.

 

[EdStainless]

How much it matters depends on the intake.
With short runners made to optimize low end torque it doesn't really matter as the flows will be slower.
At top end with long runners ever bit of air flow resistance matters and smoother is better.
An ICE is just an air pump.
Anything that obstructs air movement is bad for performance.

 

[GregLocock]

An exception to that is cold start with carbs, where a rough surface finish can help get some of the pools of fuel in the intake up into the moving air. Hopefully that is not a significant issue any more. I suppose it is possible that turbulent air might help the combustion process but I imagine going through the port will introduce far more turbulence than a rough intake.

 

[lucky-guesser]

Performance heads are "ported", where the surfaces are ground smooth (as opposed to the rough cast surface) to promote airflow. This would apply to intake runners as well.

 

[BrianPetersen]

If there's no fuel mixed with the air (i.e. upstream of injectors), smoother is better but this being a boundary-layer effect, my money would be on "too little difference to measure". N.B. I am referring to what would commonly be described as "surface finish", not "leftover casting flash and grossly excessive corners because your sand-cast core shifted by millimeters and the way your casting core blended into the valve seat sucked to begin with".

Down near the intake valve in a port-fuel-injected application, some roughness can supposedly help with vapourisation (due to having more surface area) and atomisation (due to roughness-induced boundary layer effects) but properly quantified test results are hard to come by.

The highest-performance engines that I've seen the insides of, have 4-valve-per-cylinder intake runners aimed pretty much straight at the back of the intake valve with the port coming in at a roughly 45 degree angle to the cylinder axis, and any roughness left in the surface is too small to be meaningful.

I have seen intake ports in which what would ordinarily be called the short-side radius, has an intentional ledge or ski-jump in order to intentionally break the boundary layer away on that side of the port in a deliberately chosen location, knowing that the bulk of the flow is going to go over the top-side of the port anyhow.