I didn't install it to increase the engine's efficiency. It's there to keep as much of the blow-by oil out of the intake and combustion chambers as possible. Any amount it collects will always be a positive result versus having no catch can at all. There really aren't any cons to adding one. I consistently drained about 2.5 ounces from mine at every 5K-mile OCI. A couple oil changes ago, I stuffed a stainless scrub pad in it to increase it's coalescent efficiency and I'm now almost filling those 3-ounce cups that I drain it with. So, there is room for improvement. Since trapping oil particles out of the flowing air is the key, running two of these in series should show further improvement. I'd like to know if there's a better design that has the efficiency of two of the ones I have before I mount a second one. I'll never be able to recommend NOT running a catch can on one of these engines.