Dumb supercharger question...
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Le Mans Master
Joined: Jun 2003
Posts: 5,409
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From: Kentucky basketball is life the rest is just details
Dumb supercharger question...
Alright so maybe I should have noticed before now, but the other day as I was driving up the on ramp to the highway I left the car in second and ran the RPM all the way up to redline at around 1/4 throttle. I glanced at the boost gauge at around 5K and noticed it wasn't putting out any boost...just sitting at 0. So now I'm curious and when I shift into third I go to WOT and, besides the car going sideways, it made its 7 psi.
Now this may be a stupid question but I always thought an s/c was tied directly to RPM and had little to do with throttle position. I know turbos have wastegates to do this for them, but s/c's do not. So now I'm just curious what on the s/c system controls this function? I've heard of a blow off valve...is this its function? I'm just trying to learn all I can about the system.
Sorry if this is a :_dupe: and thanks for any input. :cheers:
Now this may be a stupid question but I always thought an s/c was tied directly to RPM and had little to do with throttle position. I know turbos have wastegates to do this for them, but s/c's do not. So now I'm just curious what on the s/c system controls this function? I've heard of a blow off valve...is this its function? I'm just trying to learn all I can about the system.
Sorry if this is a :_dupe: and thanks for any input. :cheers:
Melting Slicks
Joined: Jan 2001
Posts: 2,361
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From: Sugar Land, TX USA
Re: Dumb supercharger question... (SleepieAce)
If not mistaken, on my Vortech, you have to got to WOT where the manifold pressure drops to 0 which triggers the BOV and allows boost to build into engine. Bet someone comes in to educate both of us. :thumbs:
Drifting
Joined: Apr 2003
Posts: 1,764
Likes: 31
From: Fort Collins CO
Re: Dumb supercharger question... (MySea5)
You guys have basically got it - the BOV is open under light throttle conditions, so you don't see pressure at the manifold, even though there is pressure in the piping before the throttle plate.
Differential pressures between the pre-throttle body and post-throttle body locations are what determine the behavior of the BOV.
Under part throttle, you see relatively higher vacuum. The vacuum signal at the manifold is run to the top of the BOV, and the boost signal is on the bottom. So, when you have high boost, but low vacuum, the boost pushes the BOV's valve open, and it recirculates, rather than going through the motor.
When at full throttle, there is no differential between the manifold and IC piping, and so with equal pressure on both sides of the BOV's diaphragm, the spring pressure of the BOV keeps the valve shut against the boost.
-Jake
Differential pressures between the pre-throttle body and post-throttle body locations are what determine the behavior of the BOV.
Under part throttle, you see relatively higher vacuum. The vacuum signal at the manifold is run to the top of the BOV, and the boost signal is on the bottom. So, when you have high boost, but low vacuum, the boost pushes the BOV's valve open, and it recirculates, rather than going through the motor.
When at full throttle, there is no differential between the manifold and IC piping, and so with equal pressure on both sides of the BOV's diaphragm, the spring pressure of the BOV keeps the valve shut against the boost.
-Jake
