I bought a used GZ pump off of a member on here, it was the next higher price unit above the cheapest one and it pulls around five inches at 5000 RPM in neutral on my 505 C.I. BB wedge bracket motor. That motor has 1/16,1/16 3/16 ring pack and it wasn't built for a vacuum pump to start with so that may have something to do with that low reading My next motor will have a Moroso three vane vacuum pump on it, I'm shooting for between 12 and 15 inches at or above 5000 RPM with .043,.043 and 3MM low tension ring pack so maybe that will seal better