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Its 5.25 with filter. Didn't you say you were told the engine was just rebuilt? Then there should be little IF ANY carbon in the cylinders. I sent you an email about the causes for mechanical noises in the engine. But on a fresh rebuild it will not be carbon.
reasons for engine knocks and other noises:
Pre-ignition (incorrect plugs)
Timing - early timing causes knocks similar to carbon
Crankshaft worn or main bearings burned out will cause a dull knock when accelerating under load
Crankshaft end play excessive will be indicated by intermittent knock
Connecting rod bearings worn or burned out
Loose wrist pins
There are about a half dozen more reasons.