Runner/Port wall thickness.
 

When porting cylinder heads, whats the minimum thickness for the port walls? How much pressure will the cylinder heads see, what about on a boosted application that will see up to 20psi? Will the aluminum heat up enough to make it weaker in thinner spots, enough to say "blow a hole through the side of the wall"? And what are you DIYers using to measure thickness, since a caliper doesn't exactly fit in there very well. I've got my heads ported pretty much to the max just by feel alone, but would like to know if any more porting would be possible/helpful.

How do you have them "ported to the max" by feel alone? What are you "going by"?

Pinching the walls between my thumb and index finger. You'd be surprised how close I get on measurements just by doing that. Plus I practiced on a set of junk heads and deliberately ground through in a few spots just to know how far I can port. Aluminum sounds different against a carbide porting burr when it gets thin. So between the sound and feel, I can judge pretty well how thin walls get.

But how thin is "too thin"? 20 thousandths? 30 thousandths? 1/4 inch? :)

That's what I'm wondering. Is "just right" for a NA application "too thin" for a boosted application. Whats the general rule of thumb?

It's a good question. I don't have an answer except to say that enlarging the the areas where it would get real thin probably wouldn't gain anything by being a few thousands larger. The exception may be the pinch area where the pushrod runs between the ports. That's the area of the port with the smallest cross section and it pays to widen this as much as possible. Which gets back to your question!

Rich