Abrasive flow finishing

[Chris Conlon]

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Hi,

First I owe a big thank you to Tom Cloud, Tony Cooper & everyone else who helped
me out w/knock sensor info. It's amazing how black boxes aren't so dark once you
break 'em open ;)

> I read in an article on the net (or was it a magazine)somewhere about the surface
> texture of ports in a cylinder head. It was something about the benefits of porting.
> What they mentioned was that the exhaust side would benefit most from having a smooth
> finish vs the intake. 

I was thinking about the "random bumps reduce drag" effect. Perhaps there's a
difference between drag on an object in free space (planes, golf balls) and mass
flow through a tube. It seems weird, but it might be true. Supposedly when you
have laminar flow over a surface the flow speed right at the surface is near 0,
increasing (as distance squared) to whatever max value "far" from the surface.
I *think* that this nice, smooth flow over the surface also provides maximum
drag, kind of like being perfectly wrapped in sandpaper. The bumps cause turbulent
flow, which results in little pockets of air where the "sandpaper" isn't touching
you... and thus less drag.  Where I think the difference between free space and
a tube lies is that, in a tube, the turbulent flow near a dimpled surface has to
intrude into the limited flow area of the tube itself, where it interferes with
and reduces the smooth flow that was there. Clearly more of a problem in smaller
tubes. Anyway that's my thought. Someone with a better understanding of
aerodynamics please feel free to correct and clarify this!


> One reason mentioned for leaving the intake side unpolished is
> to help the turbulance effect which serves to homogenize the fuel mixture for more
> thorough combustion and thus better power.

I have heard this enough that I'm willing to believe it. But it says one thing
to me, which touches on one of my curmudgeony theories, and that is "the fuel
isn't evaporating thoroughly." Comments? Is this just a well-known fact?

   Thank you for your time,
   Chris C.

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