Well this isn't good. We have developed a knock in a 383 stroker. It sounds like piston slap. It only happens at very low idle or under load (stopped and in gear- it's an automatic). We did a hot compression test and found that #7 is running about 25 pounds higher than the rest. Most are running about 170, #7 is running at 200. We just ran it and started disconnecting plug wires one at a time to see if we could get the knock to stop. When we disconnected #7, it stopped knocking.

So the question is - why is #7 compression so high? Or why are the rest so low?