Ok so I have never really worked with turbos. Manual boost controllers work by controlling the pressure which the wastegate releases at correct? If that is the case why does the stock blow off valve not release before the wastegate and keep the manual boost controller from working? Also how do you test a stock air bypass valve to make sure it is working?
The wastegate actuator causes the wastegate to open when a certain level of pressure is reached. A manual boost controller bleeds off some of the pressure the wastegate actuator "sees", causing it to delay opening. By changing how much boost is bled off (adjusting the manual boost controller), you can adjust what the maximum allowed boost will be.
The a blow off valve sees two different pressures. It sees the pressure in your intake pipes on the back of its diaphragm. It also sees the pressure of the intake manifold by means of a vacuum line connected to the BOV on the front side of the diaphragm. When the throttle plate is closed, pressure builds up in the intake pipes on the outside of the throttlebody while the inside of the intake manifold stays at a lower pressure (or vacuum). This pressure differential is what causes the BOV diaphragm to open, allowing excess pressure in the intercooler pipes to be released. Once the pressures are equalized, the BOV closes again.
These two systems work together but the manual boost controller, if connected properly, has no effect on the BOV or any other system except for the wastegate actuator to which it is directly connected.
To test a stock BOV, simply apply vacuum to the fitting where the vaccum line control signal enters. Use a Mityvac and observe the gauge when the diaphragm opens.
So will you see something open on the blow off valve? We are having boost issues on a MKIII Supra.
You cant necessarily see the valve opening. Depends on the design. Some of them you can.
Pulling full vacuum on a BOV wont necessarily make it open. They are designed to have the decel vacuum of the motor (higher than idle vacuum, 20"+) AND the positive pressure in the intake to open the valve, and to close when the positive pressure is vented even if there is still high vacuum.
If it is leaking under max boost that is all in the BOV and not something the air lines going to it can cause, pretty much.
You can see if it's leaking by stopping it up or removing it and seeing if your boost level changes (assuming manual boost controller).
We are making 6 psi from 2500-2800 rpm and then losing some of that boost until 3500 when it climbs up to 10 psi.
More than likely you have a boost/vacuum leak somewhere else in the system. It could be as simple as a split coupler or a blown-off vacuum line. Pressure testing your vacuum system is a good way to determine what's leaking.
Google "boost leak tester" and you should find numerous forum threads on how to make your own tester. You could buy one from silicone intake systems or some place like that as well for about $30.
Ok so do those aftermarket BOVs do anything to improve performance?
Most of the stock BOVs are not adjustable. Aftermarket usually is. That is your basic advantage. I'm setting up a second on the RB20. The stock will stay, because it cycles and is quiet, while the second will release at a higher pressure and go WOOOSH!... which I like.
It sounds like you're confusing a blowoff/bypass valve with a pop off valve.
A pop off valve opens when the intake exceeds a certain pressure, and is mainly used in turbocharged racecars, where the rules may require one in order to restrict performance. CART/ChampCar used to use pop off valves.
A blowoff/bypass valve is similar, but it opens when there's vacuum in the intake manifold, and is used to vent (or recirculate) the pressure in the intake in order to prevent surging the turbo compressor when the throttle plate closes.
As for why you would loose boost in the midrange, I'm not entirely sure, but I'd start by disconnecting the manual boost controller and running the wastegate straight off the compressor outlet signal (you are giving it that, right? Not a signal line from the manifold, right?). Mechanical wastegates usually work pretty well at giving flat boost curves (sometimes with a bit of sag or creep at the top end), so if you're still seeing wonky boost with the mechanical wastegate then you know you've got something wrong with the basic turbo plumbing. If the mechanical wastegate works fine, then you know there's something wrong with the way the manual boost controller works.
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