I recently had an engine failure and started checking everything out. I got it dyno tuned properly across the board and had no lean conditions. I was running around 11 psi. When I broke down the engine, I found that 3 of the six pistons were chipped, melted. They were all on the front back 2,4,6. The furthest (2) from the throttle body was all the way through loosing total compression. The middle of the front bank (4) was chipped moderately, the closest (6) was chipped slightly. I think that the plenum's uneven distribution of the air caused the problems. So I'm looking for another plenum now . If you have a better reason this may have happened, let me know.