I didn't have a high performance free flow exhaust to go with it. The pump didn't discharge as well when the engine was really hitting it good. I could hear the air escaping from the bypass in front of the check valve used to prevent backflow.
A good low restriction exhaust would spare all of that, but I can't stand the sound of a loud exhaust. An exhaust that pronounces itself with a really good sound is one thing, but just loud is just annoying to me.
At the end of the day, I feel it was a waste of time. It's a lot easier just to route the hose to the air box than to modify the exhaust.
There's no need for venturi in the exhaust anyway. Use one pump, and you'll get 7-9" on a vented crankcase (has a small air inlet to allow fresh air in). Double up and run two pumps in a series and you'll get 16-18" vacuum.
I wouldn't do that, because too much vacuum in an engine not built for it can cause the wrist pins to run a little dry.....so I've heard.
I first did this because I was dealing with an engine that had enough blow-by to force oil out of pretty much anywhere, including the PCV system. I attached an extended oil filler neck, and stuck a 5/8" nipple through the top of the neck just below the oil cap, to keep it from being an oil vacuum pump. Catch can in between that and the vacuum pump.
Engine runs completely dry to this day. I could replace the seals and what not, but I'm interested to see how long this trend lasts. So far it's gone 27k miles without exposing a drop of oil. I'm liking where this is going.
I've also run these systems with no vent at all, to where you had to struggle to remove the oil cap, and it released with a loud pop.