I may be jumping the gun a little bit, as my helper hasn't ruled out all other possibilities. It is his opinion that piston slap is causing false knock. We asked for .004 piston clearance but my shortblock builder didn't double check it. When he asked they said they clearanced them to .005 like a typical SBC and that it should be fine. Buddy who's helping me with it says it should really be .0035 on these LT1's due to the reverse flow cylinder head cooling (less metal expansion).....(Speed Pro forged pistons). He says he can hear the slap and it appears to be causing the false knock. Anyone else dealt with this? Any way to fine tune the frequency for the knock module to listen to so it will ignore slap sounds and still listen for knock sounds?

He thought of maybe taking some torque out of the sensor in the block. Hopefully it could still hear knock but not be able to hear slap?