Hi Bill
I had a similar situation a few years back, which turned out to be an exhaust valve guide, which initially came loose under hard acceleration. It subsequently slid back into place and was fine for a while ( I drove a lot easier after this) but eventually it came loose again and I knew it was time to get the head serviced. Joe A. helped talk me through this and his understanding was, as Al mentioned, that exhaust valve guide leaks don't end up in the cylinder and actually burn off the hot manifolds without entering the combustion chamber, so the plugs looked fine. Apparently because of the different expansion rates, the bronze guides can become loose with age and some folks have even resorted to having the guides knurled in an attempt to keep them in place. The new guides are slightly oversized and require machining to fit properly. The cost of the guides themselves was under $20 each, so I just replaced them all along with seals and haven't had any smoke since in over 20,000 miles. As Joe pointed out, if the problem was rings/pistons, the head would need to be done anyway and often the bottom end is fine, with the top end needing work 2 or 3 times before the bottom needs attention, so head work would not be wasted if you had to do a complete rebuild later.
I certainly have an embarrasing memory of the day I tried to blow past a little old lady and buried her in smoke so bad she had to pull over...a virtual fog machine on wheels :evil:
