Well, it may seem from the photos above that I've opened my ports more than karldergrosse using my porting method--perhaps even "overported"--however, I guess that a great deal of what you will wind up with depends on the original LIM casting (as mentioned by kdg already), and on gasket part number and/or manufacturing tolerances (like we've been told in this thread: http://www.bonnevilleclub.com/forum/...ic.php?t=72094
I took digital caliper measurements of the inside of the ports both before and after porting, as well as the inside of the gasket hole, at these points:
And the results are:
Point A (inside LIM port, at top, below corner radii): Before: 0.8125 in, After: 0.8880 in
Point B (widest spot in LIM port, at casting seam): Before: 0.9515 in, After: 0.9520 in
Point C (width of inside of gasket hole): 0.9670 in
Point D (height of inside of gasket hole): 2.0070 in
(Oops, also measured the height of the inside of the port hole, but forgot to draw a line for that in the pic above...that was: Before: 1.8750 in, After: 1.8955 in)
Being that the target is 0.9" wide by 1.9" high, my porting stayed within that...except of course for at point B, where it was wider than 0.9" to begin with.
I am curious kdg, since they change/update frequently, what is the exact part number of your GM gaskets (mine is 89017825), and could you take some calipers to the inside of your gasket hole? It could be that your gasket hole is significantly wider than mine...
Edit: Again, kudos on an excellent job...I think we'll both be OK with our respective portings (even if yours look better than mine