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The lean mean donut machine
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I'm pondering whether or not to do some minor porting to my Edelbrock RPM Air Gap intake manifold in search of more upper RPM power. Is this worth the time in terms of power gains or is it just a waste of effort that will do nothing but make the manifold look better from the inside?
 

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It certainly cant hurt to port match it to your heads. I dont remember from other threads what you have, but my Dart 230's were alot larger than my ports on my Victor Jr. intake. Plus being the EFI version I had big injector bosses sticking down. I decide it would be worth the few hours to port match and grind down the injector bosses. Like I say it cant hurt.

I found that a 1/2 inch drill and a HSS cutter worked very well on the aluminum. The slower speed seems to keep the cutter cleaner than trying to use a die grinder.

Chris
 

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The lean mean donut machine
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Discussion Starter · #3 ·
I took advice from an earlier thread on grinding aluminum and ordered a die grinder bit from Goodson. Man that thing chews fast and never clogs up either.

Just wondering, in addition to port matching the intake gasket area, is any work on the plenum going to help?
 

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Port matching the intake side of the manifold will definitely help upper rpm hp. If the intake is bigger than the head intake port, it will cause puddling though. If the intake is smaller than the head intake port, it will increase velocity of the a/f mixture. As far as the plenum, I'd leave it alone. If you get it too smooth, it will hurt atomization of the a/f mixture.
 

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Shop Owner And Troll Hunter
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If it is a divided plenum, you can remove some of the top center and it will improve the upper rpm range. If it is an open plenum leave it alone.

Troy
 

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It's best to buy the manifold that best matches the size of your runners. That way the whole manifold will be sized properly. Then as recommended above, do the port matching routine. And high speed grinders work great w/ carbide bits on aluminum if you use grinder's grease that totally prevents sticky aluminum clogging of the teeth Eastwood sells it. I have a tube that has polished three tranny cases, several intake manifolds, etc., etc., and still has many projects left. Probably a lifetime supply for a hobbyist.
 

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I have an add on question. I plan on working a Dodge 383 with MPI for the future, I'm planning on welding bungs onto a Edlebrock single plane manifold and matching it to a set of Edlebrock heads. I want to see if I can port the heads myself and I will match the heads and intake to the gasket. Question is, would I get any performance out of porting and polishing the single plane? I would think that it would. Most of the plenum will just be air, so I wont need the vaporization effect in that area. Oh almost forgot, I am looking at turbocharging it also. I feel that the smooth surface should help in the plenum, especially for the fact that it will be a positive charge. Any comments?
 

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Big Blocks Rock said:
I have an add on question. I plan on working a Dodge 383 with MPI for the future, I'm planning on welding bungs onto a Edlebrock single plane manifold and matching it to a set of Edlebrock heads. I want to see if I can port the heads myself and I will match the heads and intake to the gasket. Question is, would I get any performance out of porting and polishing the single plane? I would think that it would. Most of the plenum will just be air, so I wont need the vaporization effect in that area. Oh almost forgot, I am looking at turbocharging it also. I feel that the smooth surface should help in the plenum, especially for the fact that it will be a positive charge. Any comments?
I dont think there is any more need to polish the intake on a turbo application. However, I have read that a perfect turbo intake would have only an open plenium all the way to the valves rather than split ports. Personnally, I am not going to be the first person to try that:)

Chris
 

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Big Blocks Rock said:
I have an add on question. I plan on working a Dodge 383 with MPI for the future, I'm planning on welding bungs onto a Edlebrock single plane manifold and matching it to a set of Edlebrock heads. I want to see if I can port the heads myself and I will match the heads and intake to the gasket. Question is, would I get any performance out of porting and polishing the single plane? I would think that it would. Most of the plenum will just be air, so I wont need the vaporization effect in that area. Oh almost forgot, I am looking at turbocharging it also. I feel that the smooth surface should help in the plenum, especially for the fact that it will be a positive charge. Any comments?
I don't understand your statement "Most of the plenum will just be air, . . . .". Hopefully the plenum will be filled with a perfect mix of air/gasoline so the vaporization requirement will be the same as any other manifold. Smooth isn't necessarily desirable in intake manifolds. The turbulence caused by rough surfaces is useful in mixing and vaporizing the air/fuel mixture. If your car is a race car running @ 3000rpm and up, by all means get the single plane. However, if you want to do any amount of street driving, stick with the perfomace dual plane design.

On this subject, does anyone know if someone is still offering the 'extrusion' process where they force a paste loaded with carbide grit through a manifold, thus opening up the passages? It was hyped in the rod magazines for a time in the 90s and I have heard zero about it since.
 

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polishing intakes

I highly advise against polishing intake runners both in the intake and the head. The problem with polishing them is that it allows the fuel air mixture to become unsuspended, costing a lot of HP. What you want is a florentine finish. Something to do with laminar air flow, and since Im not an aeronautical engineer, I wont try to explain it. What I do understand is that you need a certain amount of roughness in the surface of the runners and ports to keep the fuel air mixture suspended.

Polishing on the exhaust port side, however, is an excellent idea.
besides not needing the rough surface to keep the fuel air mix together, polishing the exhaust side reduces the ability of carbon etc to cling to the runners causing restriction.

I heard a lot of hype about extrusion several years ago, but the cost was so prohibitive, compared to any benefits. I think it kind of died on the vine.

You dont want to just go in and start cutting down the divider in a dual plane, indiscriminately.
There is an outfit in Wisconsin called Brezinski that specializes in doing this with factory steel intakes for stock car racing, where stock intake manifolds are required. They also do a lot of other internal work in the intakes.
Ive talked to them a few times. It takes a lot of time and work to get that just right.
Take too much and you mess up a manifold, take too little and youve done nothing.

Plenum chambers are a very finnicky area to play around in.
 

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Right, it's not for the novice. I've see a lot of butchered intakes at swap meets. The norm for the street on a duel plane is one inch deep and two inches long in the center of the divider. other than that it would take a lot of flow testing.

Troy
 

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Re: polishing intakes

Max Keith said:
I highly advise against polishing intake runners both in the intake and the head. The problem with polishing them is that it allows the fuel air mixture to become unsuspended, costing a lot of HP. What you want is a florentine finish. Something to do with laminar air flow, and since Im not an aeronautical engineer, I wont try to explain it. What I do understand is that you need a certain amount of roughness in the surface of the runners and ports to keep the fuel air mixture suspended.
You are correct. To make a short story long, gasoline in an intake manifold likes to condense into a liquid (@ its dew point in the manifold at many temperature/pressure conditions) and liquid/air don't distribute equally plus liquids do not burn - only gasses burn. To keep the gasoline vaporized or at least well atomized and in suspension in the air stream, there must be turbulent flow in the intake manifold runners. Turbulent flow is a precise technical term but it's meaning is pretty plain in non-technical terms.

There are several ways to induce and sustain this turbulence. One is to have the gas go around a bend which induces turbulent flow. Most manifolds don't have sharp bends so the only other alternative is to add roughness to the passages. Envision the gas flowing in a conduit and the molecules in direct contact with the conduit wall are by definition not moving. The next molecule out is moving a little but due to friction with the stationary one, it is not as fast as the next molecule out. Speed of the molecules increases as they are spaced away from the wall. This virtually no-flow region is termed the boundary layer and the thicker this is, the worse it is for an intake manifold. Continue looking at the molecules as you go to the center of the flowing stream and you will find they get faster and faster until the very center ones are fastest of all.

There is a definite break-over point in any flowing stream which is a function of fluid viscosity, velocity, and conduit roughness where fluid goes from 'laminar flow' with a very large boundary layer where there is no turbulence to the desired full turbulent flow which nearly eliminates the boundary layer. In the former case, gasoline will tend to condense and drop out of the stream causing many problems so it is good practice to design the intake runners with significant roughness.

Incidentally, this is why golf balls are designed with the rough surface - by breaking up the boundary layer of air flowing over it's surface, the ball will fly significantly farther than a smooth ball. This drag or resistance to flow by very smooth surfaces can be overcome with aerodynamic design which is why airplanes and race cars can be smooth and go fast but for shapes that can't be designed that way like golf balls, rough surfaces are preferred.
 

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Max and willys,

You are missing his point. On a MPEFI intake there is no fuel in the intake. Fuel is injected at the head entry point. So, intake port finish is not needed to keep fuel suspended. Only in the head is this an issue.

Chris
 

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TurboS10 said:
Max and willys,

You are missing his point. On a MPEFI intake there is no fuel in the intake. Fuel is injected at the head entry point. So, intake port finish is not needed to keep fuel suspended. Only in the head is this an issue.

Chris
Hmm . . . I recall the initial question was about an Edelbrock RPM air-gap manifold which I though was a carburetor application. Correct me if I am wrong.
 

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Race it, Don't rice it!
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Willy, Some circle trackers of old are stilll doing this to there exhaust manifolds or those bound by rules with stock two barral intakes, steel heads, No porting is often a rule to help keep cost's down. Everyone knows rules just drive up the prices of power, leaving the poor man to suffer against a team with money. I currently know no one who does, for I've never asked for it. But I do know its still around.
 

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EXTRUDE HONE

Willys, the method was called extrude hone, and I think an abrasive clay like media was used.

I've done something similar to this before, which is kind of an extreme sand blasting operation. High air pressure and some fairly rough sand ran though a port for a period of time.

I've even finished hand port jobs with fine white silica sand, and it really smooths the work out.

The rougher sand does more "removal" , and the finer sand leaves a cleaner finish. I usually do this after hand porting, because the effectiveness works better on iron that has already had the factory porous cast removed.

It will surprise you how much you can change the port by doing this. Does it help? I think it does to a small degree. After all, if you are blasting sand suspended with air through a passage, the airflow through it is similar to air/fuel mixure passing through the port on a live engine.
I like the asthetics of my work after blasting it, but that's more fit and finsh than anything else.

Alot of racing rules prohibit this practice as well as acid porting
 
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