Originally Posted by jeff denton
Oh, speaking of which, does anybody know anything about acid porting, you know, to hide the tool marks you just milled into your port openings?
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Jeff, I've tried hydrochloric acid (recommended by a chrome-plater friend of mine) for this before. It just happened that he had a 200 gallon tank of the stuff, so that was convenient as well.
We didn't use the acid to hide tool marks, but rather to enlarge the runners on intake ports. A piece of 1/2" polypropylene plastic was bolted to the intake face of the head to seal it, and a silicone plug inserted into the valve guide. The head was tilted so the valve seat was level, and acid was poured into the intake runner until just below the valve seat. Then you wait.....
In all, we let it sit overnight, drained it, refilled with 'fresh' acid, and then did that again two more times to get the results desired. Effectiveness apparently depends on the temp of the acid (we should have heated the head on a surface place in retrospect), and the acid concentration (I have no idea how strong his acid solution was.). So it was three days in this case, but you just fill it up and go home for the night, then drain and measure the ports in the morning. No waiting around really. IIRC, we removed almost 1/8" from the intake ports of a 'stock' class 305 Chevy head! But you didn't hear that from me.....