Im trying to understand one small thing here, is there ALWAYS vaccum pre blower rotors on a PD blower like a Whipple or a TVS for example?

Im trying to tweak my PCV system but i need this small piece of information first.

 

There is always vacuum after a closed T-body.

 

There is also a vacuum in front of the throttle body, but not as much as after a closed one.

 

Simple answer, yes there will always be some level of vacuum pre rotor inlet. This vacuum will be the highest at high rpm with the throttle blade closed, lowest vacuum at low rpm and wide open throttle blade. When you consider the entire intake track, that is when blower displacement, inlet size, throttle body size and intake tubing factor in to determine how much intake vacuum you will have and where you will have it.

 

ok so what happens during WOT high RPM, is there still vaccum BEFORE the supercharger rotors but after the throttle body? I guess that was what I was trying to ask but didnt word my question properly

 

Assuming the throttle body is not a restriction (Which is a reasonable assumption) then the pressure before and after the tb will be the same, a partial vacuum per bernoulli's equation.

 

Just curious, what tweeks are you making to your PCV system? I am thinking of changing mine up from the current setup of a breather on the pass side valve cover and a catch can between driver side pcv valve and inlet manifold behind throttle body. I do like the idea of using the blower inlet vacuum to evacuate the crankcase fumes under normal driving but I don't thing my current setup is providing enough ventilation under wot as the breather will be come saturated in oil and drip on the headers. My current solution is to use a remote mounted vented catch can with -10 from each valve cover. This would be great for wot but would eliminate the vacuum source for normal driving. If I could place a vacuum source at the valley cover, I think it would give me the best of both worlds however this is unrealistic with the Kenne Bell occupying that space.

 

ok let me tell you what im thinking of, and im saying this without looking too close at my engine, the LS7's have a vaccum source under the valley cover. The drivers side breather hose goes to the supercharger after throttle and pre supercharger rotors so it pulls vaccum during cruise/part throttle, however the passenger side breather line goes to the filter which means its just circulating air this way.

I will cancel out the passenger side breather and put a vented catch can with a CHECK VALVE. This way the driver side breather connected to the blower can pull vaccum on the crankcase aat any part throttle/cruise scenario, and in case of WOT if there is the slightest hint of positive pressure in the crankcase the check valve will open up and vent the air out of the vented catch can while holding any excess oil in the can.

I think it will work nicely but im not sure.

 

I think you need to do away with the check valve as you are going to want a fresh air source for the crankcase. I have read that too much vacuum in the crank case will pull oil off the rings (someone please correct me if this is wrong), although some vacuum is good for ring seal.

 

well then were stuck, how can you get "little" vaccum if youre using the intake manifold as a source of vaccum youre gonna have to live with whatever vaccuum it pulls, not sure either but maybe someone can let us know?