To clear things up, I’m not saying that people can’t tell the difference between a smooth running engine and a rough running (misfiring) engine. I am saying that when people switch from one brand of oil to the next and claim that the engine is smoother and quieter, that it’s all in their heads, or they are comparing the hot oil with the thicker fresh cold oil. Switching between oils of the same viscosity won’t change anything. Going from a 2.7 HTHS oil to a 3.5, maybe, but not from one oil to another that has the same HTHS, and certainly not from mixing up two different brands