I had a set of Big block heads and a port matched aluminum intake manifold. i have since sold the heads, but my question is: can I use this intake on another set of heads when the ports won't match up perfectly. The ports have been opened up on the intake and I think the air will be crashing into the heads as it tries to enter the intake port. Short of having the heads ported, what can I do?

your a 100% correct in your evaluation. if not portmatching the heads next best thing is a new intake

You can get away with a mis-match if the head port is larger than the intake manifold port, but not if the intake port is larger than the head port. The smaller head port will creat terrible turbulence and cause poor performance, due to the "lip" that will protrude into the port.

So, why does the rectangular intake on oval port heads not slow the car waaaay down - that's a significant mismatch of much bigger intake than head port??? I've seen dyno runs on a 555 to check what a port match is worth and it was less than 5 hp on a 925 hp engine, everything else remained the same. Ports weren't waaay off, but over 1/8" in several spots.