polishing ports a "myth?"

SON240sx Automotive
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Trying to see if my thinking is correct. Read this and then discuss:

The whole point of polishing ports and cumbustion chambers is to keep carbon from sticking to these places. Suggesting that you should polish only your exhaust ports and cumbustion chambers. You polish the exhaust ports to keep carbon off them and you polish your combustion chambers for the same reason and to aid in reducing hotspots.

Furthermore, you do not want to polish your intake ports for the following reason. Based on flows in pipes, laminar flow is caused by smooth pipes. The head of the flow will take on the shape of a porabila because the centre is flowing faster then the outer parts of the flow. Why you ask? Because the outer parts of the flow is sticking to the smooth surface of the pipe. Meaning the flow there is slower then the centre.

So, applying the above you would think when air and fuel are entering your engine. Fuel being heaver then air, that the fuel would stick to sides of your ports and flow slower then the air causing an ill effect to your air fuel mixture. It would make more sense to have a rough surface to keep the flow turbulent and keep the fuel kicking back up into the air.

Andrew.

2

I guess I’m a dumbass, but I thought the pupose of polishing the intake
side was to alow the air to flow better, with less turbulence/resistance.

Thus following the theory that more air = more power.

3

I read that you want to leave the head a little bit rough to promote fuel mixture with the air.

Either way, port, polish until its pretty smooth, its not going to be perfectly smooth, its been proven to create power, can’t argue with that

4

porting opens up the ports and alows more air to flow in at a given time. Polishing is a whole other thing. As I said above, its not for flow its to reduce carbon build-up.

Looking at it from a fluid mechanics prospective, polished intake ports would cause crappy combustion since the fuel isn’t kept fully mixed with the air. If the flow is turbulent little swirls will be kicked up off of rough portions keep the fuel mixed in the air. Fuel is heaver then air so if the ports are smooth your going to have your fuel sitting on the ports and flowing in slow.

BTW I’m talking about the head and not the intake runners.

Andrew.

5

I didn’t know it was for the purposes of reducing laminar flow, but I have heard before that you should only polish the exhaust ports.

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yep a P&P should be reffered to as a PPP with the final ‘P’ being ‘prep’ as in conditionn the intake port to promote turbulence smoth flow means less turbulence, less turbulence means less air/fuel mixing creating hot psots and poor expasion during ignition. brush head to X hatch the intake after you’ve cleaned it out or ported it is what you want to do.

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A perfectly smooth, polished intake port or manifold runner will have gasoline condensing on it.

You need and want some fine roughness to discourage that, and to induce a bit of turbulence and tumble to make the mixture as fine as possible.

8

My thoughts exacly. Thanks roto and spite for confirming that for me. Sometimes my schooling does help out in the real world :lol:

Andrew.

9

That seems right in theory, would figure it’d be still true in practice. But instead of polishing the intake ports, wouldn’t it make sense to do just port and do swirls to promote better mixing of air/fuel?

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