Minimal blowby means a sound engine. See a youtube test. With crankcase well sealed and oil cap tight, block Valve Cover vent. If engine shuts off in > 10 sec, little blowby. Crankcase pressure builds until it pushes out the vacuum shutdown valve.

Others describe a bad injector spray as "nailing", like hammer taps, not a thudding sound. I have a pop-tester, which also lets you judge spray pattern.