Manifold porting

[Vikingdude]

So I have a spare intake manifold at home. As I wait for my bottom end stuff to get machined for my 383 build, I thought I would take a crack at porting the intake manifold.
My goals for this project are very small improvements in flow. If I wanted huge numbers, I would ditch the stock manifold/injection system. I'm not looking to rework the runners in a big way. I'm more scared of having a negative impact on flow, but without access to a flowbench.... it's all just guessing.
The stock lower vortec manifold has a lot of cast in ridges surrounding the ports. I have about 3 hours into this so far with a flame shaped carbide burr. Next up is 80 grit cartridge rolls, followed by 100, and 120s.
I'm open to any criticism, critique, or advise anyone with experience porting might have for me. This is my first attempt at this, sobi expect there is a lot of room for improvement. I'll update as I make progress

 

[Orpedcrow]

I was think about doing the same with mine while I have it off. Thanks for sharing.

 

[L31MaxExpress]

If you are sticking with the stock Vortecs, go with a composite fiber gasket like the Felpro 1255 or Edelbrock 7235. The dimensions of them are very close to the vortec head ports. My manifold was opened up to the larger gasket size to match my ~210cc heads, but I have ported several to the smaller dimension. Do not port match to the larger OE gasket dimensions.

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[L31MaxExpress]

Even with 210cc ports my manifold ports are still smaller than the OE style gaskets. The 7215 Edelbrock Etec 200 gasket that my heads and manifold were ported to are a different look than the stock port. They are a larger rectangle shape.

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[L31MaxExpress]

This is why I say to use one of the fiber paper gaskets. The fit is excellent, in addition to them lasting much longer than the plastic/rubber or metal/rubber garbage. Glue the gaskets in place with Edelbrock Gasgasinch to hold them where they belong while you install the manifold. The paper gaskets have the correct port dimensions to transfer to the manifold prior to cleanup port work.

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[tayto]

This is why I say to use one of the fiber paper gaskets. The fit is excellent, in addition to them lasting much longer than the plastic/rubber or metal/rubber garbage. Glue the gaskets in place with Edelbrock Gasgasinch to hold them where they belong while you install the manifold. The paper gaskets have the correct port dimensions to transfer to the manifold prior to cleanup port work.

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do you use stock bolts/torque specs here (11ft-lbs) ?

 

[Orpedcrow]

This is why I say to use one of the fiber paper gaskets.

That’s seriously close!
Is that head gasket matched?
What do you put on the opposite side of the gasgacinch? I’ve used grease on paper gaskets with good results.

 

[L31MaxExpress]

That’s seriously close!
Is that head gasket matched?
What do you put on the opposite side of the gasgacinch? I’ve used grease on paper gaskets with good results.

Head has stock ports, no gasket matching done to them. I use gasgasich on both sides, I replace intake gaskets in/when removed. I learned my lesson on that years ago on a TBI that I had to replace a roller lifter on right after the first startup. The intake gaskets looked perfect, I reused them and then ended up with milkshake.

 

[pressureangle]

You're on the right track. Simply radiusing the intakes improves flow enough to matter. One important thing to know is that a gasket that is larger than the port, when sandwiched between to matched ports leaving a gap, has no meaningful effect. As a general rule, there is a boundary layer of air that moves slowly against the port walls, so the airflow never sees that gap. Flaws that cross the port cost more than flaws in line with the port. Sharp edges are never good except on the valve itself.

 

[L31MaxExpress]

You're on the right track. Simply radiusing the intakes improves flow enough to matter. One important thing to know is that a gasket that is larger than the port, when sandwiched between to matched ports leaving a gap, has no meaningful effect. As a general rule, there is a boundary layer of air that moves slowly against the port walls, so the airflow never sees that gap. Flaws that cross the port cost more than flaws in line with the port. Sharp edges are never good except on the valve itself.

Radiusing the entry helps as does thinning material in the center divider for more of a knife like shape. I also opened up the ports to the edge of the plenum, so that with the plenum installed, it could help guide air into the ports rather than the air coming off the plenum slamming into a ridge thus disrupting flow from turbulence. That is mostly theory but I can guess it does make a difference. I sacrificed a cracked plenum by cutting the top out of it. I then bolted it in place and used a scribe to mark the lids alignment to the ports.