Talyn said:
So, making the intake manifold ports slightly larger than the head ports is the best way to go then?
Slo-Sho said:
That is the not so smart way to go. Having a rough surface area lets a 'layer' of air adhere to the surface. Since air can travel more easily over air this is beneficial.
The first line threw me off, but I think Slo is saying exactly what Talyn was getting at. Then, I started thinking the gasket was actually smaller than either the head or manifold ports, hence my next remark (I have absolutely no idea why I thought this, in retrospect- gasket matching can't work with a gasket opening smaller than either piece)
Slo-Sho said:
Gasket match is really all you need, although you can enlargen the gasket as well if you care to do so. Just don't make a ledge from the intake to the head...
I thought I had it figured out up to this point; Slo and Alex are taking contrary positions. Okay, no problems.
alex22 said:
You should not look at the intake port, gasket and intake manifold as one tube, not 3 pieces.
~Alex
Just an extra "not" in there? It seems to make sense again, but we're getting two conflicting perspectives. The first is that the lip created by having a smaller port on the head than on the manifold shears the boundary layer, and the second that a match of the ports on both sides (I believe this is what is commonly referred to as gasket matching- line the gasket up on both pieces, trace, grind until they all align) results in cleaner, unrestricted flow (unless I'm reading this wrong), but then, this.
alex22 said:
The gain in performance would have to do with how the boundary layer reacts to the step, i'm not sure what happens there.
One thing that is often overlooked is how well the header lines up with the port, many times the header is shifted to one side, you should check and then port accordingly.
~Alex
he mentions misalignment of the manifold and head, which would create some sort of lip which would obstruct the airflow. Why would this be worse than intentionally creating a lip?
So there's 3 situations now- smaller head port, larger manifold port; equally sized and aligned ports; and then slightly offset/misaligned ports. That's what I'm not understanding fully. I hadn't given much thought to any of this, but Alex's comments on the bulge created by gasket-matching (sort of the reverse of a Venturi), and the theory about the boundary layer and the Nascar testing all seems reasonable.
Part of my misunderstanding was due to some really odd thinking on my part. Having realized my fundamental mistake, I'm still trying to figure out if the difference in manifold and head port sizes is good or bad. Maybe it's just me, but it's not readily apparent which is the better situation. Would a smoother intake mean a thinner boundary layer? If misaligned ports create an obstruction or restrict airflow, isn't intentionally restricting the air uniformly worse? Is any of this even (the percentage of power gained /lost) relevant to our (or at least my, nearly stock) 4.0s? I think I'll just crack a beer.