Yeah, I'm skeptical about the exhaust system causing the problem since it doesn't seem to be restricted at all. The technician said that the timing was right at the specified advancement. He retarded the timing a little bit on the chip's program to help save the engine. Also, I forgot to mention that it only pings under heavy load, but not necessarily WOT. I can be cruising along in 2nd gear at about 2500rpms, then suddenly put the pedal down an inch or so and hear the preignition for a second or so until it self adjusts. That'd be really cool if you could ask your mechanic about it! Thanks for posting.