Gasket matching vs. port matching.

[iScamp]

I"ve asked this question to a couple of people and they don't seem to understand what I'm trying to say.
We've all seen or are engine builders that gasket match intake runners to cylinder head ports.
The intent is to make a seamless transition from the intake to the heads.
No step. Got that.
However, the intake gasket is always larger than the blueprint dimension of the intake port by design. I was told by one manufacturer their spec. is .030" larger all around for the gasket. Many times I've seen .060" excess gasket border dimension on SBM engines. So when you grind away the port to the gasket size; you are taking the intake port cross section area, only at the mating surface, way beyond it's blueprint dimension.
I was told this really doesn't affect flow. Maybe so. But, why do it if your intent is to blueprint (or close as you can).
There is an aluminum intake for sale here on FABO and apparently someone has gasket matched the ports. You can see the expansion of cross section area in the pictures. Really got me thinking about this.

 

[famous bob]

I"ve asked this question to a couple of people and they don't seem to understand what I'm trying to say.
We've all seen or are engine builders that gasket match intake runners to cylinder head ports.
The intent is to make a seamless transition from the intake to the heads.
No step. Got that.
However, the intake gasket is always larger than the blueprint dimension of the intake port by design. I was told by one manufacturer their spec. is .030" larger all around for the gasket. Many times I've seen .060" excess gasket border dimension on SBM engines. So when you grind away the port to the gasket size; you are taking the intake port cross section area, only at the mating surface, way beyond it's blueprint dimension.
I was told this really doesn't affect flow. Maybe so. But, why do it if your intent is to blueprint (or close as you can).
There is an aluminum intake for sale here on FABO and apparently someone has gasket matched the ports. You can see the expansion of cross section area in the pictures. Really got me thinking about this.

I use hughs gaskets , for a r/b , I match all three...

 

[iScamp]

Why do you grind material away to reach the edge of the gasket?
Just asking an honest question. Sometimes the head intake port mismatch may only be a few thousandths of an inch or may even match without any grinding.
I'm thinking once you grind enough to take care of the mismatch, there is no reason to go any further.

 

[famous bob]

Why do you grind material away to reach the edge of the gasket?
Just asking an honest question. Sometimes the head intake port mismatch may only be a few thousandths of an inch or may even match without any grinding.
I'm thinking once you grind enough to take care of the mismatch, there is no reason to go any further.

in my case the cnc`d victor type heads were a fair amount bigger than the intake , could have got by with it I guess , but that aint my way , always want the max. ...

 

[C130 Chief]

The gasket port sizes are sometimes oversize as you note, and so are the mounting bolt holes. Also, what if you wish to open the port size beyond gasket size? The answer is a transfer plate. Start with a sheet of metal approximately gasket thickness, drill for bolt holes and install between the head and intake. Now, drill a pair of .125 holes trough the intake flange and plate into the cylinder heads. These will serve as locating pin holes. Remove intake and grind port openings in plate perfectly flush with ports in head, transfer plate to intake manifold and use as template for grinding intake ports. Modify gasket as necessary. Now you know that with the engine assembled the ports will in fact line up.

 

[iScamp]

I have done the port matching using a template before. The original port mismatch was very minimal in the one engine I did. If I had gasket matched, I would have had to grind away a significant amount of metal.

My question; why grind to the gasket outline?

I've seen dozens of videos of this. Guy sets the gasket to the head and scribes the outline. Grinds away metal to the scribe line. Repeats for the intake.
If you are only trying to correct the mismatched port, what is the point of going all the way to the gasket edge?

Grinding that much metal increases port size in that local area and would slow airflow. Correct?

 

[RustyRatRod]

Gasket matching and port matching are not the same. Is that what you're getting at? You can port match without gasket matching and gasket match without port matching. ....and I reserve judgment on whether gasket and or port matching increases flow until I see results on a flow bench. It's not something I would just arbitrarily say "no it does not" without proof, because I believe in a lot of instances it certainly does, especially if the transition from intake to cylinder head is smoothed out, opened up and made as one.

 

[iScamp]

"made as one" I get that's a good idea.

Yes, I'm saying port matching and gasket matching are two different things.

Port matching is correcting the head/intake mismatch just enough so the runners are aligned. Make a template method.

Gasket matching is grinding the head/intake runners to meet the edge of the gasket. This will increase port cross section area over a short distance. Removes a lot of metal beyond what is necessary to bring the port in alignment.

"Why gasket match" is the question. That takes time and effort to grind the additional metal away to the gasket edge. When removing a small amount would get the transition smooth.
Plus a large change in port cross section area for a short distance.
Why grind to the arbitrary size of the gasket opening?