I figured I would start a thread to help the endless stream of guys who are asking questions basic about these devices (either in tandom or by themselves)
To control the boost in your SRT your need a "wga" waste gate actuator (to move the turbo wastegate) and a boost controller in one form or another be it PCM, electronic aftermarket, manual or bleed/bleed tee. Remember the turbo will literally spin itself out of control in a self perpetuating cycle without boost control. And boost control is gained by use of boost itself.
The waste gate actuator holds the wastegate shut by virtue of a spring/spring tension. This spring can be provided and in turn purchased at different rates ie: 4 psi, 7, psi, 14 psi, etc. The waste gate when installed in a relaxed arm position (no pre tension of the spring) will maintain the wastegate closed until the boost pressure equals or surpases the rated spring pressure.
Pre-tension or "tunning" the wga by adjusting the actuator arm length in effect changes the spring rate (making the spring "stronger") and will hold the waste gate closed at even higher presssures (with no real limit which can be dangerous).
The wga has a diaphragm side which is pressurized by the turbo boost pressure (via the "green line" blue line" black line" etc) which when it reaches a high enough pressure will overide the force of the wga spring (assuming the spring is of a correct range and the wga is not over-tensioned) and force the wga arm to move and in turn open the wastegate.
A boost controller determines at what pressure and or how much pressure is allowed to flow to the wga diaph and cause it to move or start to move open.
Your SRT4 PCM/ECU is an electronic boost controller in and of itself and a damn fine one at that. It commands soleniod#2 by electrical signal to modulate open and pulse boost pressure flow to the wga on a graduated scale in response the relative position on the "boost table". The PCM will use boost to control boost.
A manual boost controller will accomplish boost control in a similar fashion, except it normally reduces the pressure that flows through it thereby artificially creating a reduced boost pressure being passed along to the wga. For example you may be actually boosting at 15 psi, but the manual boost controller is set to only pass 10 psi along to the wga, so its 12psi spring is not moved by the 10 psi, all the while its actually boosting at 15 and would normally be coming open by then. Of course a mbc is an all or nothing proposition and does not offer any graduated control based upon gear/rpm. Electronic boost controllers are required to accomplish this type of control.
A manual bleed also accomplishes the same thing as a MBC its just not easily adjustable. The bleed tee simply lets some of the boost preesure to escape to atmosphere so an artifically high boost pressure is required to actually move the wga arm (its like trying to blow up a ballon with a hole in it)
Running a aftermarket wga without a bleed, mbc, or keeping it on the stock pcm is very primative and counter productive. The pressure line you run to your wga is always going to be "on" or "fully pressurized" with whatever the boost pressure happens to be at the moment and affords no adjustment whats so ever. The diaph will always be charged and attempting to move the spring constantly. Its actually the safest way and will provide control, but its far less affective than even the stock arrangement.
Running a aftermarket wga with to large of a bleed or a boost controller set to aggresively can be very dangerous and even wreck your engine because the appropriate motive force is not being sent to the wga diaph. Over adjusting your wga arm can create dangerous levels of pretension requiring far to much boost pressure/force to open.
I offer this "primative" explanation in order to help some of the new guys gain an understanding of whats going on with their wga/boost controller mods
Any and all comments/clarifications are completely welcome and evn encouraged.
I have attempted to explan things in "simple" terms so please keep that in mind. I realize ceratin mechanics have been omited/simplified.
In closing remember YOU USE BOOST PRESSURE TO CONTROL BOOST PRESSURE via the wga. Its as simple as that
Boost controllers and wga's basics (how they work together)
Linear Mode
