bypass valve operation

[bikerdan]

Does the by -pass valve begin to close and begin to build boost at exactly O PSI or does it begin closing as the vaccume begins to reach 0 PSI? It sems I have more pull even though I am not in + boost on the gage. This my be due to tune.

[jordan 572]

Originally Posted by bikerdan

Does the by -pass valve begin to close and begin to build boost at exactly O PSI or does it begin closing as the vaccume begins to reach 0 PSI? It sems I have more pull even though I am not in + boost on the gage. This my be due to tune.

The bypass should stay shut all the time except when your in boost and you suddenly get out of the throttle, the bypass relieves the built up pressure by bypassing it back before the compressor housing so there is no compressor wheel surging. At least from my understanding, someone please correct anything wrong.

[A_VAS]

bypass is a vacuum signal operated canister, with a restricter in the vacuum line to slow it's operation. It vents off the pressurized air from the rotors under light load, cruise, idle.
As vacuum drops to near 0, depends on engine load and throttle position, it will slowly close. The boost pressure doesn't affect this canister, it only operated off vacuum. When vacuum drops, the canister diaphram closes the bypass valve and pressurized air then hits the intake ports.
That's my explanation of it's operation....at what vac reading does it start to work, you'd probably have to put a vac gage on it and drive to see for sure. At 0 vac (wot) it for sure is reacting, but not immediately since the restrictor in there slows it down. Takes 1 sec or so to fully open the diaphram if you watch in on a dyno for instance

[bikerdan]

Originally Posted by A_VAS

bypass is a vacuum signal operated canister, with a restricter in the vacuum line to slow it's operation. It vents off the pressurized air from the rotors under light load, cruise, idle.
As vacuum drops to near 0, depends on engine load and throttle position, it will slowly close. The boost pressure doesn't affect this canister, it only operated off vacuum. When vacuum drops, the canister diaphram closes the bypass valve and pressurized air then hits the intake ports.
That's my explanation of it's operation....at what vac reading does it start to work, you'd probably have to put a vac gage on it and drive to see for sure. At 0 vac (wot) it for sure is reacting, but not immediately since the restrictor in there slows it down. Takes 1 sec or so to fully open the diaphram if you watch in on a dyno for instance

Great explanation, I had no idea throttle position and load were factors or that there was a restrictor.
Thanks

[Jon@MagnaCharger]

Originally Posted by A_VAS

bypass is a vacuum signal operated canister, with a restricter in the vacuum line to slow it's operation. It vents off the pressurized air from the rotors under light load, cruise, idle.
As vacuum drops to near 0, depends on engine load and throttle position, it will slowly close. The boost pressure doesn't affect this canister, it only operated off vacuum. When vacuum drops, the canister diaphram closes the bypass valve and pressurized air then hits the intake ports.
That's my explanation of it's operation....at what vac reading does it start to work, you'd probably have to put a vac gage on it and drive to see for sure. At 0 vac (wot) it for sure is reacting, but not immediately since the restrictor in there slows it down. Takes 1 sec or so to fully open the diaphram if you watch in on a dyno for instance

Very good explanation. The bypass valve itself it actually spring loaded and at the point that the inlet reaches 3 in/Hg of vacuum the diaphragm in the actuator no longer has sufficient vacuum behind it to hold open the bypass valve against the spring's tension. This is when it starts to close and will be fully closed by the time you reach 0 vacuum/boost.

[bikerdan]

Then I am correct that I feel more HP even before my gage reads a + boost?

[Third-Gen]

Jordan 572, actually the valve should be in the open position, which allows the intake air to be recirculated through the blower, reducing parasitic losses while under light load and cruising. Once the manifold vacuum rises above a certain point (3in/hg for maggies, some are different), the valve closes, and sometimes very fast depending on how fast the vacuum drops off. If you gun it off a light, by the time the car starts to move forward, the valve should be closed. It doesnt actually "vent" off the pressurized air, since the MAF would read this as airflow, and adjust the fuel trim accordingly. It simply recirculates it behind the throttle blades.

This is a good example of how fast the valve should react, and this one is a little slow still. Most guys on the dyno roll on the throttle to not damage anything


Similar to this diagram, except electronic throttle bodies have no idle air circuit.



Jon I was gonna chime in and correct about the vacuum canister, but you beat me to it. Kudos!

The "seat of your pants" dyno is never as accurate as an actual dyno. Sometimes where you are in the powerband makes a big difference in the way the car feels. My camaro always felt like it had more power from a standstill at half throttle, only because at WOT it was leaning out and bogging down. Only way to know for sure is have it dyno tested. do a pull at 1/2 throttle or just slightly out of boost, and do a run at WOT. if you are making more power at 0psi vac/boost, you definitely have an issue!! or maybe someone hooked up the bypass valve wrong. should go directly to manifold vacuum AFTER the blower.

[bikerdan]

I was just thinking that when the bypass starts to close and I have a vaccume - the amount of vacume is reduced by some pressure fpushing past the plate partially as it begins to open . It seems very "seamless" like no immediate 150Hp as soon as I hit boost. It seems like it is building up as plate opens and I draw less vaccume.

[Third-Gen]

well its not going to be like a nitrous hit. at redline in WOT how many lbs of boost does it make?

[bikerdan]

Originally Posted by Jon@MagnaCharger

Very good explanation. The bypass valve itself it actually spring loaded and at the point that the inlet reaches 3 in/Hg of vacuum the diaphragm in the actuator no longer has sufficient vacuum behind it to hold open the bypass valve against the spring's tension. This is when it starts to close and will be fully closed by the time you reach 0 vacuum/boost.

If my calculations are right 3 Hg vaccume = 1.48PSI vaccume ?

[bikerdan]

Originally Posted by Third-Gen

well its not going to be like a nitrous hit. at redline in WOT how many lbs of boost does it make?

About 6 PSI. Kinda hard to read exact boost and watch road. If I do it in 1st or 2nd I gotta shift so quick I cant see gage and in 3rd I'm aproaching 90MPH and not seeing gage.

[jordan 572]

Originally Posted by Third-Gen

Jordan 572, actually the valve should be in the open position, which allows the intake air to be recirculated through the blower, reducing parasitic losses while under light load and cruising. Once the manifold vacuum rises above a certain point (3in/hg for maggies, some are different), the valve closes, and sometimes very fast depending on how fast the vacuum drops off. If you gun it off a light, by the time the car starts to move forward, the valve should be closed. It doesnt actually "vent" off the pressurized air, since the MAF would read this as airflow, and adjust the fuel trim accordingly. It simply recirculates it behind the throttle blades.

This is a good example of how fast the valve should react, and this one is a little slow still. Most guys on the dyno roll on the throttle to not damage anything


Similar to this diagram, except electronic throttle bodies have no idle air circuit.



Jon I was gonna chime in and correct about the vacuum canister, but you beat me to it. Kudos!

The "seat of your pants" dyno is never as accurate as an actual dyno. Sometimes where you are in the powerband makes a big difference in the way the car feels. My camaro always felt like it had more power from a standstill at half throttle, only because at WOT it was leaning out and bogging down. Only way to know for sure is have it dyno tested. do a pull at 1/2 throttle or just slightly out of boost, and do a run at WOT. if you are making more power at 0psi vac/boost, you definitely have an issue!! or maybe someone hooked up the bypass valve wrong. should go directly to manifold vacuum AFTER the blower.

My bypass setup is a bit different on my turbonetics system. I always thought my system had to vent the bov air charge back into the system rather than the atmosphere, I know it does release the charge back into the system right before the ic but I take it the only reason why it does this on my setup is to make it carb legal as the air hasn't been metered yet since the maf is near the throttle body.

[jordan 572]

Thanks for the clarifications though.

[Third-Gen]

Magnusson and turbo kits are two completely different systems. OP had a Magnusson. You cant put the MAF after the blower so the bypass valve has to recirculate the air. The centrifugal and turbo kits place the maf after the blower or turbo, so venting to atmosphere is just fine.