High Compression Setup

[XiKeiyaZI]

(Ahem) So I'm working with an engine that was setup with a higher compression setup. One thing I've noticed with this engine is during each stroke of said piston, there's a deep dull thump. Not like metal, as music slap or anything. Everything sounds mechanically good. It just sounds like a dull vacuum being ruptured. Car sounds great, runs great, performs great. Upkeep is flawless - It's just... it sounds odd to me. The engine is bored .20 over and it was built with slightly lower compression pistons. Is it usual for these to give that dull chugging noise as opposed to the higher combustion compression noises found in stock engines?

Just looking for some education.

 

[vr4scott]

The noise you hear, is this while you are turning the motor over by hand or while it's running? Are the spark plugs out? Is the oil pan off?

 

[XiKeiyaZI]

This occurs during normal running operation. It's just a very dull compression noise. Engine and performance are well above expected levels. I'm just not used to the noise. I wouldn't think that 8.7 pistons, a milled head, 272/264 cams, and a .20 over bore would cause a dramatic difference in compression noise. It did it slightly before the cam install, now it's just more prominent.