Port Matching vs Gasket Matching, which should i do?
 

I am getting ready to port my 416s.

my question is should i gasket match to a gasket, like fel-pro 1204 or 1205, and do this on both the heads, and the intake.

or would i be better off using the port size on the intake (Weiand 7525 Port Size: 1.94" height; 1.15" width) and make a gasket based on the ports on the intake, then transfer that over and port the heads to match the intake?

or option #3 -- the one you suggest?

this is the first time i have ever ported anything, and need to know what the best way to do it is. and what is going to get me the most power!

You should port match. You can use the gasket as a guide.

The most common problem with gasket matching is the way people do it. They just enlarge the first 1/4"-1/2" to match the gasket on both the heads and the intake manifold. This causes the end to be bell mouthed. It's very large compared to the rest of the intake runner, and will actually hurt flow.

When you get an idea of how large to make the runner to match the gasket, blend the transistion smoothly about 1"-1 1/2" into the runner. That way it won't disrupt flow.

If anything, it's OK to have the intake runner a little smaller than the runner in the head. It can actually help atomize the fuel more.

If the runner in the head it smaller than the intake runner, that's bad. That step will really disrupt the flow for obvious reasons. Plus the fuel will puddle up right there.

that is what i was thinking, i know alot of BB guys have alot of luck with oval port intakes on rectangler heads, because of the opening effect from the smaller intake port to the larger head port, do you think i am better off porting the heads out to a 1204 gasket, which is about 0.05" larger than the intake ports? or going with a smooth transition, it doesn't much matter to me, i am griding either way, but i want to do this right, and do it the way that is going to make the best power.

How do I say this.........?

The conservative way is the safe way. ;)

Unless you REALLY know what you're doing, you shouldn't pretend you're Sam the butcher (from Brady Bunch). ;)

Anything you do (as long as you stay conservative) will only help. All you're doing is helping the intake and heads do their job.

It's when you start hogging material away that you start to change the flow characteristics. Unless you really know what you're doing, don't do it. http://www.mx6.com/boardnew/images/s...icon_darin.gif

Use a gasket.

In addition to the simple port dimensions, the ports have to be in the same place as each other, after the parts are bolted together. There are other ways to get that right; but by far the simplest, is to use the gasket as the "indicator" for where the ports are.

As far as making the most power, if you choose the correct gasket (such as a 1204 for 416 heads and not a 1206 or something), it shouldn't matter.

Also, there's no law that says you have to port exactly to the gasket; if you decide that both the heads and the intake can be matched to .050" inside the gasket, that's good too. Again, think of the gasket as the "indicator" or measurement method, not necessarily as an absolute template.

i guess that was my real quesiton. is it better to open both ports up to the gasket, or since i know that the intake port as is is about 0.50" inside the gasket, should i leave it alone and match the head ports to that. so it is a nice smooth clean transition.

That's really up to you. When you pick up a die grinder, you're on the way to becoming an "engine builder", not merely a "parts assembler". It's a decision you have to make based on the shapes of the parts. You should carefully examine the specific parts in your hand.

Like AJ said, simply hogging both sides out all the way to the gasket may not be the best thing to do. If you can maintain a constant port cross-section through the intake, into the head, and through the head runner, you'll get better overall results than if you create an aneurysm in the ports at the gasket surface.

Certainly avoid a squared-off restriction like having the intake manifold matched to the gasket, and the ports .05" smaller. If anything, you want to make it bigger after any step change in flow area.

There is a line of thought that the head ports should be matched to the gasket, and the manifold ports slightly smaller than the gasket. The theory is that this small step will help prevent "reversion" of flow back to the manifold when the valve closes, but not have a significant effect on power. The biggest benefit of this approach is at idle/low RPM's with a cam with a lot of overlap. Mild cam engines wouldn't see much difference (but wouldn't need the porting as much, either). I followed this approach with the Camaro and it idles like stock. I haven't decided yet which way I'll go with the 396 (full manifold port matching to the gasket, or leave slightly smaller) - I'll probably go ahead and do a full gasket match on the intake (already did so on the head ports).