Acceleration and deceleration are pretty different engine loading conditions. Using the “knocking” word makes everyone think rod bearings, but even “knocking” can be different stuff. Frequency is a big thing to think about, how fast/slow it is can help pinpoint it. IE, does it match engine RPM, or valve train, or driveline revolutions.
Based on your description I would also look at drivetrain stuff, or maybe suspension. With acceleration and deceleration you’ve got angle changes with the driveline and loading and unloading of the suspension. Could be the driveline hitting the exhaust, bad or loose u-joint, or some kind of suspension interference. Bigger horsepower means bigger weight shifts and harder loading of the suspension.
Another thing to consider would be detonation, not sure what compression you’ve got, what octane you’re running, or the timing info.
