vaccum and forced induction
Thread Starter
Drifting
Joined: May 2001
Posts: 1,329
Likes: 12
vaccum and forced induction
I was thinking the other day (doesn't happen often :D) about how a blower should negate any vaccum in an engine. Am I right? And if so, how would you keep your vaccum operated accessories (power brakes, lights, etc) operational?
Le Mans Master
Joined: Feb 1999
Posts: 5,877
Likes: 1
From: Park Ridge IL
Re: vaccum and forced induction (Lohkay)
Check valves. Since the engine isn't always under boost, and does see some negative manifold pressure at light load cruise rpms, when the throttle is closed, etc, the check valves will maintain a vacuum for the headlights, hvac, and brakes - most of the time.
Thread Starter
Drifting
Joined: May 2001
Posts: 1,329
Likes: 12
Re: vaccum and forced induction (Monty)
Really? I thought that since a blower always turns, the manifold pressure would always be in the positive. Or humm...maybe not on idle, but anything above...So the check valve opens when the pressure is negative. Makes sense.
Melting Slicks
Joined: May 2000
Posts: 2,148
Likes: 1
From: Chandler AZ
Re: vaccum and forced induction (Lohkay)
Remember where manifold pressure is measured from- with throttle plates closed the engine is sucking thru tiny idle air bypass and will pull vacuum. Only after the plates start to open can the blower build positive manifold pressure. The surge valve is there to relieve turbine backpressure on the other side while the throttle is closed.
