Originally Posted by 4.whoa
I read an article about porting heads(cant remember where) and it said that you do NOT mirror polish the intake ports, just get them very smooth -200 grit IIRC. that creates a little turbulance (not sure if thats the right term here) along the surface that the rest of the air slips on (kinda like a bunch of pipes on the floor, you put a safe on them and you can push it with out the drag that you'd have directly on the floor)and the flow/velocity/cfm/ whatever goes up! Kinda like golfball dimples
I hope that came out right
edit: WoW just realized how old this thread was
You are absolutely right. Its important though to note that there are deeper reasons for this to be done in cylinder heads than simply boundary layer issues.
This is more apparent on carbureted vehicles, but smooth intake ports tend to inihibit fuel pooling , because of the lack of tension/turbulence on the liquid mixture of fuel and air. To the best of my knowledge this can still happen in a fuel injected vehicle but this is dependent on where the fuel is actually injected. If I had a throttle body injected vehicle, I would likely leave the finish rougher than our port fuel injected trucks shown here.
Let me put it this way. When I get a order for a TB, unless specified otherwise, I do a near mirror (I typically sand or wetsand with either 600 or 1200 grit then buff) finish. Why is this? Because there is a myth in the performance/hot rodding world that shine=flow. Unfortunately they do not always correlate. Why do I do it then? Because people ask for it. To the point where its easier for me to do it by default, to keep all the TBs looking the same.
From all of my experience and research I have done, in these particular applications, the extra-fine finish on the throttle body does NOT hurt flow.
Now, if its one of my own personal TBs? I stop at maybe 320 grit (smooth to the touch), maybe 600 or 1200 grit. No buffing. Why? Because it just isnt necessary. The only thing it might aid is in carbon buildup....but thats what Catch Cans are for.
That polish makes for a negligible difference. Trust me, if I could get away with it and sell my TBs just with a smooth grit finish and not polished I would! Buffing/polishing is by far the most time consuming part of the process...Its not fun. Because I am stuck working on a given TB, trying to get it smooth and shiny, for 0 gains. I could spend an hour less per TB and still have the same great effects.