CNC Mill Mark Removal in Intake Port

When considering mass airflow then the burr finish or whatever method is used to rough up a surface you can mostly see that on a flow bench.

After spending a stupid amount of time on the dyno watching the numbers and such that it isn’t really about mass airflow but it’s about eliminating or more accurately reducing wall flow that’s always present when and where fuel is added to the intake.

Getting that wet fuel off the surfaces and back into the airstream can pay big dividends.

You just have to overcome the way some people think in that if the jet size gets smaller than orthodox they panic and rather than learn they want to stop because they are sure it’s going to eat itself when the fact is it’s getting hurt with all that unneeded fuel running through the engine.

That makes sense. A 'macro' rough finish (as opposed to a sandpaper like finish) would be expected to create a bunch of little eddies which keeps the flow energized near the wall and maybe more importantly is going to create little depressions that help vaporize fuel back into the airstream. It also seems like it would help the port operate over a wide range of velocities/flow-rates which would likely help the gear change a whole bunch too.