reactor2

Turn up your volume (its hard to hear over the engine noise, supercharger, and new pulley chirp that just showed up this spring). This is a cold start. About 22 seconds into the video you'll here the clacking/knocking start (loudest at 33 seconds) and about 18 seconds later it will be completely gone. It doesn't do this on a warm start, it generally has to sit overnight for this. Oil pressure is good (40-42psi at idle).

Piston slap, lifter clack, or?

Maybe carbon build-up amplified piston slap (its always had some noise on a cold start just never this pronounced)? Would a few techron treatments help?

http://vid296.photobucket.com/albums...no35/knock.mp4

reactor2

I'm leaning towards lifter noise, anybody else? The reason is that it seems to be something related to oil pressure. If the lifter in the last spot in the oil channel takes awhile to get fresh oil then that could explain the 15 seconds of noise. Everything I've read about piston slap is that it takes several minutes for it to go away, not 15 seconds.

73Corvette

Use the old broom handle or long screw driver trick to PIN POINT where the sound is coming from... I know its a short window... be ready and have someone else start the car and find out where the sound is coming from...if, it's a lifter you should be able to get right on top of it and have a good idea exactly which one it is...

reactor2

Every once in a while my car starts in self preservation mode (p1516), not sure why. Today I let it run and the clacking noise seemed to be much less pronounced. Hmmm,now I'm leaning towards piston slap.