I have a SBC 377 and over reved it today and now I have a knock but only at idle and it is a solid knock not a tapping my oil presser gauge reads 20psi at idle it has a scat forged crank and the crank was ordered with the right main journal so I didn't use spacers any ideas what it could be

 

Spun rod bearing or bad wrist pin is the most common source of a knock.

Main bearings don't knock. Spun cam bearings don't knock.

Getting a knock after over reving the engine could still be a failed rod bearing (stretched rod bolts). You could have floated the valves and at least one is now bent.

Doesn't really matter. If your engine has a knock, it will need to be stripped down for repair. The longer you put it off, the worse the damage can become.

Pull all the spark plugs to see if one is damaged.

 

Yeah wrist pin is what I was thinking would it still have good oil presser if it was a spun bearing the engine only has 25000 miles on it