"Polishing the intake ports can show slight improvements in air flow, but
can hurt power. A rough texture will make some turbulence at the port walls.
Fuel has a tendency to run along the port walls, especially on the outside
of turns and the floor. A rough texture will help keep the fuel suspended in
the air. Unless you really know what your doing, don't polish the intake
I know someone here who works in a junk yard was planning on, has done this
because they were going to ad an RV cam. What he said is basically what I
said, and I was just guessing. It seams like he knows what he's doing.
Lets convert that last paragraph to english.
I know someone here who works in a junk yard was planning on/has done this
because they were going to ad an RV cam. What that page said is basically
said at the time, and I was just guessing. It seams like he knows what he's
There's more to ports than the average person would think...
Have you ever tried adjusting the length of an exhaust pipe on
an engine (ie: drag pipes on a harley)? It makes a huge difference
in the sound due to the wave-length of the sound, the rythm of the
engine (speed dependent too), and so-on. So not just the polish of
port, but the rythm and operating speed have allot to do with it.
there are the turbulant/laminar flow considerations. Generally
laminar (smoothe) flows easier/faster. However, the turbulance
(roughness) can counter-act some of the rythmic tuning issues (ie:
polish it and get a 'dead-zone' at a specific RPM, roughen it and make
the tuned points fuzzier in tone and thus the engine more tolerent).
Got a blower? Ram air? If you're not going that far, and it's a
low-cost car it may be fun to experiment with. However you'd probably
get more out of a set of headers. And like headers, it will be hard
to prove it's really different without a power-test (got a place to do
a 1/4 mile? - my guess is less than 1/4 second on a ~15 second time).
Please let us know the results if you go through with this - if it
really kicks ass it wouldn't be too hard for me to pull a manifold and
try it too.
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.
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!
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.