Star Machine is the nicest stuff out there, but there are alot of companies offering them. For a typical setup, pull 10-12" of vacuum. When you are looking for any little bit of power, you can raise it. Be careful...too much will starve areas of the engine of oil. We run Star Machine's mountain motor pump on our 820" motor and have it set around 16". It will tell you how good your motor is sealed up, and will help with oil leaks as well.