Port Polishing

Lets convert that last paragraph to english.

I know someone here who works in a junk yard was planning on/has done this procedure, because they were going to ad an RV cam. What that page said is basically what I said at the time, and I was just guessing. It seams like he knows what he's doing.

~KJ~

I'm afraid that's still a long way from english.

Tell me what is unclear, as in my drunken orange juice stupor I don't see what the problem is.

~KJ~

Wasn't planning on trying it. My stance (and this fellow's, in a way) was that a rough-cast finish should allow the air to go through the manifold better then a smooth surface, just like the air can go around a gold ball 'betterer' when it has dimples then when it has none. While he concedes that polishing can improve flow (Mine was just a WAG that I asked the NG to see what their thoughts were) he says it can hurt performance. Most certainly NOT why I said the rough-cast surface is best - but I wanted to bring the subject back up.

~KJ~

I happen to be an aircraft mechanic so maybe I can help a bit. A golf ball or aircraft wing is primarily trying to achieve "lift" and does this be creating "pressure differential". Other objects that must contend with the air around us do not concern themselves with "lift". As strange as it may sound, the shape and characteristics of a body designed for lift or drag will be quite different.

The surface airflow for small lowspeed objects has a characteristic "stickiness" not exhibited in larger or faster objects. A very smart aerodynamics experimeter by the name of Renold came up with a mathematical computation to estimate this change in properties based on size and speed. Co-incidentally this is referred to as the "Reynolds" number for the object.

For example a Bee or house Fly have hair to keep the molecules of air from "sticking". However, as the size and/or speed of an object increase, it's "Reynold Number" (a way of measuring how air acts) increase and the "stickiness" is no longer as important a factor as it's smoothness. Therefore, what works for a Bee or golf ball at low speeds (trying to produce lift) is not what you want at larger sizes or higher speeds; that's why bullets, cannon shells, baseballs, planes, missiles, and arrows don't have dimples or hair!

The effect of "Reynolds" numbers may be tested (to the displeasure of animal rights groups) by throwing a cat from top of the Empire State building; notice how it will walk away. Now, you jump (or push an elephant off) and notice the big SPLAT! Remaining in the pool of gook is the effects of "Reynolds" number, and its effect on size. (The elephant and cat have the same density per cubic area, but the air sees them as entirely different properties.

Unfortunately, many folks hear just enough information about some quirk in science that they misapply it by generalizations. A classic example is where many young hot rodders think that a larger carburetor is going to increase engine performance. As you know, that is only true under certain circumstances and there must be a "match" between the machine parts and engineering performance design :-)

Hope this helped! Jan Zumwalt

I do believe that you C&P this from the last time I posted my opinion about this.

~KJ~