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Old 11-07-2006, 05:51 PM
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Intake runner clean up

I have a lot of time on my hands and an Edelbrock RPM intake that's telling me I should be smoothing out/polishing the inside of the intake ports to maximize flow while I wait around. Being a novice, this "seems" like a good idea. So is it? and if so, can I accomplish the task without signing away the rest of my life and can I do it using shadetree garage type tools? I know I can screw things up big time so what should I avoid doing (besides smoothing/polishing the darn thing) Maybe I should get a hobby while I wait for parts? Thanks.

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Old 11-07-2006, 08:02 PM
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Unless you have the equipment to measure air flow. About the only thing you can do is smooth out any casting "boogers" and port match the intake. Some roughness is desired on the floors and lower walls.
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Old 11-09-2006, 11:38 PM
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I have heard that some intakes have rough areas or grooves put in intentionally to fight fuel puddling and distribution problems.
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Old 11-10-2006, 07:23 AM
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check these out.http://brodix.com/parts/turtles/turtles.html
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Old 11-10-2006, 10:09 AM
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You don't want it smooth, you want some texture. The roughness does two things, 1) creates turbulence to keep the fuel droplets suspended, and 2) creates a lovely little thing called a boundary layer. The air that directly touches the walls stalls and acts kinda like an air lubricant. If you smooth out the walls that boundary layer goes away and you're dragging air directly across the aluminum. Just smoothing the passages can reduce flow.
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Old 11-10-2006, 11:15 AM
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The reality of the matter is if you have time and it bothers you tweak away at whatever bothers you inside the runners. As long as you don't change the shape of the runners or do anything silly your not going to hurt anything. In stock form those runners flow 275 CFM or better. Unless you have a killer stock 23 degree cylinder head flow is not going to be an issue.

As for any improvement in flow, I'd bet $100.00 that it's zippo. The amount of work we do on intakes to get them to flow and match to the cylinder head runs in the $600 to $1000 range. A lot of that work is in the plenum.

So in my mind the bottom line is if it makes you feel better, and there are obvious, significant casting imperfections, grind away. The odds of gaining any meaningful flow though are slim to none.
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Old 11-10-2006, 12:23 PM
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Smoothing intake ports

Thanks for the input. I think I'll stop "fixing" it and leave well enough alone. What a great site! There is so much to learn and know and so many folks who are willing to take the time to share their knowledge. That's what it's about. So if anybody wants to know how to make killer chili verde just ask me. That, I know. I'll be B-A-C-K!
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Old 11-10-2006, 01:35 PM
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After reading this post I have a question, I'm a newbie too. Does the roughness creating the turbulance in the intake runners mean that you want the same type of roughness on the intake port of the head? If so why do so many people spend so much money on porting and polishing intake and exhaust ports? I understand that a majority of the fuel/air mixture occurs in the manifold and maybe this is the reason. I used a die grinder to remove all the excess casting flash in the runners of my heads but feared going much further than that. I contemplated grinding all the roughness in the ports smooth but decided I didn't know enough about what I was doing and figured I should stop before I ruined a perfect set of heads.
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Old 11-10-2006, 01:55 PM
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Most porting leaves the intake ports rough. Its just a carbide bit so its pretty rough when all is said and done.

When you hear "ported and polished" it typically refers to ported runners in the heads and polished chambers. The roughness of the casting in the chambers can cause little hot spots which can lead to detonation. Polishing them smooth eliminates that problem.

I do have some CNC ported heads that are very smooth, but it was just a pocket porting job; the area just inside the valve seat. The amount of distance that the fuel travels isn't really affected by 1/4" of smooth metal, especially that close to the hot valve seats. If any fuel does come out of suspension onto the walls there, its quickly evaporated again.

A full CNC porting job leaves 1/8" smooth steps the whole way through the port which has the same basic effect of casting roughness. Some shops that CNC port will also roughen up the surfaces again for you if you want after the porting. At that point though we're really chasing down the last 1/4 hp.
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Old 11-10-2006, 03:48 PM
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CNC porting does not really leave "steps". What you see in pictures with CNC ports is simply the shadowing of the cutter along the port walls. The overall finish is pretty smooth. With all the heads we port for customers they will be finished with a cartridge roll to smooth out the port shape. No matter if they go through the CNC machine, are hand ported or both.

Let's look at the bottom line here and put this in perspective. Porting a head is not a cosmetic thing. Cleaning up the walls is not going to gain you much of anything unless it is a very rough dirty casting. Bang for the buck on porting is chamber work bowl work, and that doesn't even have to "look" pretty to have an amazing affect on flow. Making it look pretty by itself is not porting.
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