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Discussion Starter · #1 ·
I was reading an article about horsepower improvements made due to porting and polishing cylinder heads. Im sure polishing is just as it implies polishing the ports or intake and exhaust ports etc. But Im not too sure what the porting aspect implies. Reshaping the ports maybe? Also, is it hard to do for a beginner, or am I better off paying to have them done. I have a 305 sbc I am working with due to money issues etc, and want to use this engine as a learning tool, not to mention I bought it pretty cheap. It runs fine, I just want to try and understand why cams make a car breathe better, and a intake lets a car suck in more fuel/oxygen etc. Thanks for all the help
 

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You have it right. When a head is ported, the contours of the intake and exhaust port are reshaped in order to improve flow. Some of the flow improvements come simply because the port has been enlarged.

The value of polishing the port is debatable for a street engine. Polishing smooths the surface of the ports and creates less friction as the air moves thru the ports. The downside to this is that less turbulent airflow allows fuel to drop out of the air/fuel mixture. Also, polishing is very labor intensive and costly for the minimal gain most people see. I suspect the real value of polishing comes into play at very high RPMs where street engines don't go.

To me, porting is one of those "black" arts that only a few people truly master. Sure, you can to a basic port job on a set of heads, but it won't come close to what a professional can do. That said, I would still do a little research and learn the basics like bowl blending, gasket matching, and general clean up. Those are worth a pretty good amount of power and you don't have to be an expert to do them. It just takes practice. I would find a set of junk heads to practice on so you can get comfortable with what you are doing before you work on the heads you are going to put on your engine.

When thinking about an engine, remember that it is basically an air pump. The more air that moves thru it, the more power it will make. A bigger cam helps an engine make more power because the bigger cam keeps the valves open longer, allowing more air to flow into the cylinders. However, this does not mean that the bigger cam will always make more power. Engine components have to be optimized as a unit as opposed to being choisen individually.
 

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When I think of porting, I always include capacity matching in there as well. That might actually belong under blue-printing, but you would have to grind the chamber some to get each to match.

It is definitely left to skilled sculpturer, not just to anyone who owns a dremel tool.

------------------
David
Camaro - '68 327 Coupe, '86 Z-28 IROC 305 TPI
Corvette - '73 Mako Shark II, '82 Cross-fire, '01 Coupe
 

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Discussion Starter · #4 ·
Thanks for the explination, I am going to try practice a little first as you mentioned. The thing is, I want to learn to do things on my own this way I know why certain changes in my motor composition make things move up or down. I like to know how things work and in doing so I get a better understanding of a part like a competion cam or dual plane intake, I am just beginning, and think I am better off learning rather than just throwing my money out there, not to mention I dont have a lot of money. Thanks for the help I appreciate it.
 

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Peter,

If you can find a junk motor and tear it down, you would learn a lot. It's much easier to understand how an engine works when you can see the parts in place. You should be able to get a small block pretty cheap.
 

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Standard abrasives has a kit I used available through JEG'S at about $40.00. It comes with instructions to clean up bowls, and match ports. They also have instructions on their website about porting. Porting or matching ports and under valve clean up is worth some HP. The kit makes it easy, but, it is time consuming. If you do your own, it will help and save you big $. I like what I've done so far on my BBC with ovals.
 

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Discussion Starter · #7 ·
Hey guys thanks for all the information and help. I am going to go to a local swap meet around here and see what I can find as far as used parts to practice on. I find working on my car very interesting and self rewarding. Thanks for the help.
 

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I saw a skit on Horsepower TV once that did a dyno comparison between bowl blending, gasket matching and port polishing. I can't remember the improvement gains specifically, but do remember this. Bowl blending gave you by far the greatest horsepower improvement followed by gasket matching. I'll guess by saying that bowl blending gave about 10%, gasket matching 5% and polishing 3%. At times, port polishing is a bad thing on a carberated motor as it can reduce fuel atomization.

You have to be careful when doing any of this, but especially when bowl blending. You can easily nick a valve seat and have to have it replaced. It is also possible to get into the water jacket, or signifintly weaken the casting if you try to take too much out of the port.

-dnult

[This message has been edited by dnult (edited 09-26-2002).]
 

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Here's what I've learned from Vizard and other good sources:
1. Don't polish the intake port if it is a wet flow port.
2. When porting, try to gain as much airflow as possible BY REMOVING THE LEAST AMOUNT OF MATERIAL.
3. Always bowl blend your ports if possible.
4. Gasket and port matching can have a negliable effect on street motors (sometimes it works, sometimes it wont, but it can't hurt I guess).
 
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