[Walt Fricke]

I share Shane's puzzlement over this, but I have always been lazy and just measured piston to head clearance with solder on one hole, and assumed that, with matched cylinders, new copper base seals, pistons, rods, and heads, plus a true case, that all would be identical.

On my latest motor, with 12/1 CR, I started with NGK 9s to be safe. These were clearly too cold after a dyno run, so switched to 7s. They seemed to be fine, though the run was short for other reasons. I can see a plug which is too hot causing the plug to break. Would that also be a source of pre-ignition/detonation? Still hot enough for the next compressiin cycle to cause the fuel to light off before it was spark time? Still leaves unanswered the question of why one bank only, with only small deck height differences between the two.