Thread: Check valve / pressure regulator to tune boost bypass actuator/solenoid?

I have some questions about a potential mod I thought of (or at least that I haven't found in any Google results.)

First, let me describe what I think I know about how the boost bypass actuator/solenoid works. Please let me know if this is correct.

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The boost control actuator is spring-loaded to keep the bypass valve closed. Inside the housing there is a diaphragm connected to the rod that opens and closes the bypass valve. On either side of the diaphragm are vacuum fittings that allow vacuum to either increase or decrease the effect of the spring holding the bypass valve closed.

The fitting to the top of the actuator is connected to a vacuum line on top of the supercharger, that taps into the area after the throttle body, before the rotors. When vacuum is applied to this fitting, it works against the spring to pull the bypass valve open.

The fitting to the bottom of the actuator goes to the boost control solenoid, then on the other side of the solenoid the line continues on to a vacuum fitting that taps into the intake manifold, after the rotors. When vacuum is applied to this fitting, it works with the spring to help pull the bypass valve closed.

The boost control solenoid, when closed, cuts off vacuum to the lower fitting on the boost control actuator. In this state, it is easier for vacuum after the throttle body to pull the bypass valve open. The ECU closes the boost control solenoid at idle and other conditions where it does not want boost (low load, reverse gear.)

The boost control solenoid, when open, allows vacuum to the lower fitting on the boost control actuator. In this state, the vacuum below the diaphragm helps "cancel out" the vacuum above it so it's easier for the spring to pull the bypass valve closed and make boost.

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Is that about it? If so, here are my questions and ideas.

1.

Does the solenoid contain any sort of check valve, or does it simply open and close the line? If there is no check valve, then is it not possible that when boost in the manifold reaches a certain point, that the line going from the manifold into the solenoid will see PRESSURE rather than VACUUM, thereby PUSHING the actuator in the direction that opens the bypass valve, bleeding boost?

If this is so, could adding a check valve in the line between the solenoid and the actuator help increase boost, or rather, help stop bleeding off boost? (Of course, check valve oriented so the actuator can see vacuum, but if there's any pressure in the line it gets blocked.)

2.

What about putting an adjustable pressure regulator (or in this case, vacuum regulator) in the line from the top of the supercharger? It could be "dialed down" to limit the ability of the vacuum after the throttle body to pull open the bypass valve. Tuned right, it could still be open at idle and low load, but would be easier for the spring to overcome and close the bypass valve.

Crazy idea? Just crazy enough it might work, or just stupid crazy?

This isn't about making "more boost" per se (I know you need a smaller pulley for that,) just tuning so it can come on quicker/stronger while still letting the PCM control when, unlike the simpler mod I've read about that bypasses the solenoid entirely.

Originally Posted by Scottydoggs

what about not touching it?

(In before lewd jokes)

Questions:

- Did I describe the operation of the boost control actuator and solenoid correctly? It that basically how the system works?

- Is it possible under some load conditions for the vacuum line from the lower intake manifold to provide BOOST through the solenoid, pushing the actuator toward opening the bypass valve? Perhaps more so with a smaller pulley?

Regardless whether or not I "touch it" I'd like to understand the system better.

Along these same lines, can the operating parameters of the BCS be tuned in the ECM? Maybe to tune launch characteristics?

Found a reference to one of my ideas (restricting vacuum between TB and top port of actuator) here:

http://www3.sympatico.ca/aepa/bypassvalve.html

Under section "Want even more?"

That's with a fixed restrictor rather than adjustable, but same idea.

As for the other part, will vac line going to the solenoid see boost, duh, it will, because it's teed off the port under the snout that also goes to the MAP sensor, and that some people tee off for an aftermarket boost gauge.