So what you are saying is that it is ok to match the intake port on the heads to the gasket and manifold as long as I'm just opening the initial edge of the runner on the head?
Scottie
I am surmising by your question wording that your manifold is bigger than the entry to the head?
If that is so, then there may already be a problem.
Ignore the size of the gaskets, they are not sized to be anything related to performance. Make your own gaskets that are the right size.
I can't say if it is okay to open up the port entry to match. Maybe it is, maybe it's not.
I would have to see the rest of the port in question.
We are dealing with a system that begins with the bellmouth, and ends in the cylinder, and every millimeter of that entire system must be designed to work together to achieve the goal. Just "matching the ends" of two parts, when it's likely that neither one is actually the right size for the system, is not getting anywhere.
This is entering an area which is a big issue with people who are just beginning to get into the performance area, and it's very common in Enfield "DIY" circles, where people just "put parts together" expecting something good to happen. I can tell you that is where a lot of people go wrong. If you look at what we do at ACE, the whole system is matched to reach a certain goal.
You need to measure those parts out, find out what the relationships and shapes are like from the bellmouth to the valve, and get some strategy going, BEFORE you cut anything.
Here's some good basic criteria.
Find out your bore size.
The intake valve should be about 53% of the bore diameter.
The exhaust valve should be about 80% of the intake valve diameter, but it might be larger because Enfield commonly used a large exhaust valve. This can be compensated in cam design.
The intake valve throat should be 89% of the intake valve diameter on a typical street application.
The port minimum cross sectional diameter should typically be about 75% of the valve diameter for a port that has the usual angle that an Enfield port has. The carb should be the restriction, for best atomization.
As you can see, this is not even addressing the matching of two parts. The matching of the parts comes in AFTER you know what the sizes and relationships and tapers and shapes need to be. THEN you can match things up.
So, given what I have just explained, IF your intake manifold is larger than the intake port entry at that junction, here is what I would do to it.
I would leave the port alone, if you are not going to do a full porting job.
I would bolt the manifold to the head in such a way that the tops are aligned for best flow, and leave the mismatch at the floor.
Then I would fill the floor of the intake manifold with some JB-Weld, and shape it so that it matches to the port entry nicely, and sand it and finish it with that rough surface finish that we discussed previously. I'm not saying to JB-Weld the manifold to the head, just use the JB-Weld to fill the floor for shaping inside the manifold to match the port floor in the head, for flow matching purposes.
Make a gasket that fits that hole exactly, and use it.
Put it all together carefully with the carb off, so you can see that everything lines up the way you want it to at the junction of the ports, and then put the carb on it.
This gets you the flow match you want, and doesn't cause potential damage to the port entry when you don't know for sure what is going to be needed to be done to the port in the future. We never want to cut ports until we know exactly where we are going with them, because if it gets done wrong, then it's very hard to deal with later on when we want to do it right.