Knock

I have seen many threads about this but just to get updated. I have a loud knock. Oil pressure stays up. Already replaced 6 lifters. How would I diagnose this further? How would I verlfy that it has a cracked exhaust manfiold?

This may sound a little primitive, however, it works and works well for certain things. Take a piece of heater hose, usually about 2' long is plenty. Hold one end to your ear and the other end near where you think the noise is emanating from. This will work for locating an exhaust leak, engine vacuum leak, vacuum leak under the dash and determining which pulley is noisy under the hood among other things, but probably not an engine knock. A piece of ¼” vacuum hose increases the accuracy in pinpointing the leak/noise. I call it "The poor mans stethoscope". Don’t knock it until you try it!

Lifters tap, bearings knock. You could have a bad crank bearing in line causing this.