Porting 420A intake manifold

[Risstanomak]

When porting the intake manifold how deep should I go into the runners?

 

[VelocitàPaola]

Do you really feel confident porting an intake manifold by yourself if you have to ask questions like these? No offense, but there are so many facets to the function of an intake manifold that this job is really only suited for a professional. Even something as seemingly mundane as the texture on the interior of the runner has consequences when it comes to performance. Porting is definitely something I wouldn't want to attempt without many years of experience, and maybe a flow bench...

 

[Blitzeclips]

I agree with ^^^^ on this one. Although I can't say the same for myself. I used my dremel w/ the flex shaft. Essentially you want to knife-edge the runners to increase the velocity of air passing through. I went about 4-5 inches back. Then switched the wheel to polish pad and polished it all up.

 

[Risstanomak]

Thank you, I appriciate the concern and I love this forum. I'm a tuner noob but not a metal working noob, I do subtractive scupting with all mediums, I'll get that surface to a mirror.

 

[VelocitàPaola]

I'll get that surface to a mirror.

That's what I'm saying... a mirror finish isn't always best, especially you were "polishing" a wet manifold. Since we have dry manifolds, however, a mirror finish would be fine (in the intake manifold, not the intake ports).

 

[Risstanomak]

Interesting. What are the physics behind having the smoothest possible finish being bad for air flow? When you say the intake ports do you mean the lower half the manifold that bolts onto the head? What is the point in porting the manifold if the ports on the head arent the same size too?

 

[Blitzeclips]

That's what I'm saying... a mirror finish isn't always best, especially you were "polishing" a wet manifold. Since we have dry manifolds, however, a mirror finish would be fine (in the intake manifold, not the intake ports).

Sounds like Paul is referring to the exterior of the manifold, rather then the inner part. I think he's saying even the micro-scratches caused from polishing can deter the rate of airflow? That's what I'm getting out of it...

I don't know though, I was told by a good friend who studied motors in Florida for 4 years, that the best pattern would be of a golf ball on the inner ports. Since a golf ball is designed to fly rapidly through the air, I'm assuming this would be oopposite effect when reversed(object flying through air vs. air flying through object). I can't say I agree with him though, so don't hold me to that.

 

[Risstanomak]

Whaaa? You guys are just trying to confuse me so I won't port it. A golf ball has dimples to produce lift the same dimples cause drag so any drag in the manifold doesn't seem good to me. I'm p&p the ports that attach to the head and the ports that mate together of the 2 manifold halves to a smooth surface using the gaskets as templates. Now I'm seeing that the ports on the head itself are smaller than the gasket used as a template. I didnt notice this before I had started porting the ports on the lower manifold. Should I just stop there or have the intake ports on the head enlarged to match?

 

[bullettdsm]

Polish away, my friend. What Paul is refering to (when he says "wet manifold" - Paul please correct me if that's not what you are refering to)) is a manifold that has both air and fuel moving through it . You need to have a somewhat rough surface inside to generate a bit of turbulance to keep the fuel from puddling somewhere within the manifold. Our manifolds are "dry" in that they only have air moving through them. If you look at the location of the injectors you will see that their spray is located at the head, therefore, you can polish the intake without worrying about the puddling.

As for porting; You can actually make your air flow worse. Bigger is not always better. That being said what I did was knife edged the dividers inside of the head and did a bit of porting within there. I also opened up the initial part of the chamber a little and matched it to the intake side. I took out the "humps" in the intake manifold and opened up the runners a little....................

BUT I DO NOT RECOMMEND THAT YOU DO ANY OF THIS!!

I have seen/worked with different porting processes and heads over the years. I wish I had a flow bench, but I don't. What I am doing is making educated guesses based on past experiences. I ruined heads to get to the port that I think is OK. Mine is an approximation that I'm comfortable with. Some may disagree but that's racing.

I would suggest that you just do the polishing and maybe a little porting to fix up casting irregularities. You can go further. My next step would be to cut down the humps (at the injector port side) some. You will want to measure each one as you do it to try to maintain a consistant size.

I'm not trying to scare you out of this, just giving info.

Mb

 

[VelocitàPaola]

Polish away, my friend. What Paul is refering to (when he says "wet manifold" - Paul please correct me if that's not what you are refering to)) is a manifold that has both air and fuel moving through it . You need to have a somewhat rough surface inside to generate a bit of turbulance to keep the fuel from puddling somewhere within the manifold. Our manifolds are "dry" in that they only have air moving through them. If you look at the location of the injectors you will see that their spray is located at the head, therefore, you can polish the intake without worrying about the puddling.

Precisely.

 

[Risstanomak]

Ah, I see. I have ported the head end of the manifold to the inner diameter of the gasket. I'm sorry I did that because now I have to match the head to that diameter. Will I have to adjust the fuel/air ratio if I port the intial intake part of the head to match the gasket inner diameter? If I do I'm thinking of just sculpting some jb marine weld to make up for the part I shaved away on the manifold A Frankenstien monster manifold. Simply put: Will I be ok if I match the intial part of the head to the newly sized ports of the manifold? After this I swear I wont probably wont have anymore questions for a long time

 

[VelocitàPaola]

By all means, ask questions. That's how you learn.

We aren't grumbling over the questions, but rather, the risk to your car. My advice would be: stop where you are, and wait until you have the resources to have a professional port the head. Having those mis-matched air passages will pose much less of a problem then a head that's been improperly ported.

 

[Risstanomak]

Sensible enough. I'll just smooth the manifold and be done with it. Thanks for the education.