This is a topic that comes up often on the list, and we
get many questions about it....so after a few requests i wanted to post to the
list about the full boost control system on the Sy/Ty.
Most understand the system, but many of the newbie's don't understand the full concept at all, or are a bit fuzzy on it.
The turbo spins via exhaust gas pressure, exiting the turbo through the exhaust housing. It spins the exhaust turbine, spinning the compressor wheel, creating a pressurized environment in the intercooler/intake. The boost level is now determined by the amount of air moved by the turbo. The turbo's amount of air moved (not considering turbo efficiencies here) depends on the the rpm of the turbo, and that is directly related to the amount of exhaust gases/pressure present in the exhaust housing of the turbo. So, more load/higher RPM, there is more exhaust gas, leading to more boost.
How is boost controlled?
Exhaust gas pressure needs to be lessened in the exhaust housing. So exhaust pressure needs be leaked out at a controlled rate, either before the turbo or directly from the exhaust turbine. In the stock Sy/Ty system we have an integral wastegate (integral to the turbo, part of the exhaust housing). Many use an external wastegate, (not part of the turbo), and before the turbo, at a crossover pipe, or part of the exhaust manifolds.
The integral wastegate has an orifice that directly leaks gas out of the exhaust turbine. The wastegate puck seals this orifice shut, so no gas can leak out. Think of it as a door letting exhaust gas out or not letting it out, depending on its position (from fully closed to fully open) the exhaust exits at different rates, or not at all. This puck is connected to an arm, that is visible outside the turbo. Move the lever back and forth, that is the wastegate opening and closing. No resistance at that part (there shouldn't be). It is connected to the actuator, and actuator arm. The actuator is a pneumatically operated device that converts air pressure to a linear motion, using a diaphragm and spring. The actuator will move the arm fully open at ~10-12psi of pressure. So with no solenoid in the system, and a boost pressure source connected directly to the actuator, you will (should) get 10-12psi, as that is when the wastegate will be opened by the actuator directly.
Why do you get more boost with a different chip/boost controller?
The solenoid is a device that goes between the boost pressure source and the actuator. This modifies the actual pressure/air that goes in the line to the actuator. So if you have 13psi, and the solenoid is restricting air to the actuator, it may not see that full amount of pressure, maybe 10psi. So the wastegate does not open yet. When it is 15psi boost, the actuator may modify the source so that the actuator 'sees' 12psi, and now opens. The solenoid does this by using a duty cycle of a small mechanism (I tore one open the other day, looks like a small needle valve with spring tension). With varying duty cycles, the solenoid lets more or less air through, out of the solenoid. On Diacom this will read as 100% when the wastegate is clammed shut (desiring more boost) and much less than that (30-70%) when the ECM is commanding the solenoid to let full boost thru to open the wastegate via the actuator.
With the stock ECM/calibration, and some aftermarket controllers, this is a closed loop type of operation, meaning it reads the boost via a map sensor, then adjusts the wastegate duty cycle based on the desired boost level, in order to increase boost (close wastegate a bit) or decrease boost (open wastegate more).
There is more to come on this subject, including...
Wastegate arm adjustments,
Aftermarket boost controllers,
Common boost control problems and remedies,
Possibly some diagrams/pictures.
Wastegate Arm Adjustments.
The wastegate arm (or wastegate rod) is the connection from the wastegate actuator to the wastegate lever itself. The wastegate lever itself is free moving, swinging freely. If it does not move freely (when disconnected from the wastegate rod) there is a problem, something impeding movement, and this needs to be fixed. Some stick intermittently, or only when HOT.
The wastegate actuator is spring loaded, clamping the wastegate closed when there is no boost source. When pressure is applied to the actuator, the actuator opens the wastegate. The rod's length can be adjusted, which means that the wastegate itself will have a different rate of bleeding of the exhaust depending on the adjustment. Good pictures and diagnostic tests are in the Syclone/Typhoon Service Supplement (on the CD Rom I believe).
The wastegate rod is connected to the wastegate lever. The lever has a pin, the rod slips on to it, and a retaining clip through the wastegate lever holds the arm/lever together. If you pull the pin, and slip the rod off the lever, the hole on the arm and the lever's pin should overlap slightly. In the manual it states to look for 1/2 overlap, so you'd have to pull the arm out of the actuator slightly (tight spring tension here) to connect the arm to the lever's pin. I believe the overlap spec has been updated so factory specs are now 7/8 overlap (basically a looser/longer rod setup). The arm's length can be adjusted as the rod end is threaded onto the rod. Tightening the end will shorten the wastegate, loosening lengthens it. If the rod is shorter, the wastegate is clamped more tightly shut. If the rod is longer, the wastegate is held loosely shut. If the rod is shorter, the actuator requires more boost pressure to open the wastegate the same distance as if it were adjusted longer. Result - more boost, faster spool up, as the wastegate is not opening quite as much, and not as quickly. The opposite goes if you lengthen the rod.
If you are using a feedback type of control (3 bar chip/aftermarket high performance controller) the adjustments won't have the same exact effect as it would on a non feedback type of control (ANS controller, bleeder valve, stock chip if you are running more than 15psi, as it cannot feedback control boost levels it cannot sense). On the non feedback controlled setups, adjusting your wastegate rod will adjust your boost level, and its response. On a feedback type of control, adjusting the rod will adjust the response more than the full boost level reached. It will affect the actual boost level, but it will usually take a more extreme response to do so, since your control system will take this change into account (with minor changes that is, but if you tighten TOO much, the wastegate may not be able to reach full open to bleed off enough pressure, not to mention what your wastegate can flow period). So you can dial in your wastegate rod to give you results closer to what you desire, as long as your system is working up to par. The actuator can also be out of spec, and there are full diagnostics for making sure it is working as it should.
An external wastegate is a wastegate that is designed separate from the turbo itself. Some externals have been used in designs that mount it near or on the turbo itself though (Turbonetics has some designs like this, the ATR setup for Sy/Ty's is this way). Externals typically have a lot more flow capability than integral wastegates (sometimes you'll see HP ratings for wastegates). Most have dual port actuators also. This setup uses two ports on the actuator diaphragm in order to initiate movement of the wastegate's shaft/puck. This can make for a quick opening wastegate, for better spool up/control.
Many people mount externals on the crossover pipe on syty's (on Buicks as well) with great results. Kenne Bell headers have a mount for a Richard Lee external wastegate on their crossover pipe. If you want to use one on a stock type Sy/Ty, you'll need to custom fabricate a mount for your wastegate. Most external wastegate kits include a flange for mounting purposes.
If you are making a HIGH HP ( 500+ ) Sy/Ty, an external (or multiple) is the ONLY way to go. The output of these wastegates can be routed back into the exhaust, or vented to atmosphere (LOUD!!). If you do vent to atmosphere, you can put a pipe/muffler on the output to quiet it some. I use an HKS wastegate mounted on my crossover pipe, with a simple regulator for control. Boost is rock solid and easily controlled.
www.turbonetics.com - See Deltagate/Racegate.
www.hksusa.com - HKS has 2 models of wastegate also.
Aftermarket Boost Controllers.
In my book, there are 3 different types of aftermarket controllers. The first being non electronic, basically adjustable bleeder valve/regulator types. These are no more than hyped up pressure regulators, as used in air compressor systems, fish aquariums, industrial pressure applications. The hardware is usually just a knob actuated device with vacuum connections. This design works fine, as long as you have a wastegate that works GREAT. Otherwise, these are subject to spikes and boost creep.
Boost spike - when the boost level spools up and shoots past the set limit, then settles back down.
Boost creep - boost slowly rises over the set boost level.
The main thing here, is that if you think of using one of these, you can pay a lot less by buying one from a different source (usually $20-50 rather than $75-150).
I usually think of the last two (electronic controllers) in two different categories. The simpler one being basic controllers that will put out a simple duty cycle to your solenoid, or use a different solenoid that just varies duty cycle on twists of the adjustment knob. These are usually cheaper, and don't provide for the same performance as the higher end electronic controllers. The duty cycle remains the same on the solenoid, letting the wastegate start creeping open. Also, should creep/spikes occur, the controller does nothing to fight this.
The more complicated electronic controllers (Greddy Profec, HKS EVC, Apex, Blitz, etc.) use a feedback control setup. They know what the boost level is, via a map sensor (usually internal), and will adjust their controls based on what the current level is. When installed correctly with a good performing wastegate, they provide for solid control with great spool up. The fuzzy logic ones claim to 'learn' the characteristics of your turbo system, supposedly making them able to eliminate spikes and creep. These setups are more expensive, and can be a pain to install and program. From what I've seen, if you have a bad performing wastegate, one of these setups won't help matters. If your wastegate is up to spec however, one of these controllers will work fine, and may even give better performance.