Wastegate
 

2008 HHR SS, 172k miles 2.0L

Can I weld my wastegate closed on my 08 HHR SS? I'm thinking that the deverter(blowoff)valve will regulate the boost pressure. I have pressure tested my wastegate actuator, which is most likely wore out. (Shop test) It was starting to open at 6psi and completely open at 11psi. (Road Test) Boost was dropping off at 10psi on a third gear pull. So turned the adjusting nuts down as far as they would go, which shortened the leakage rod as far as possible. (Shop test) It was now starting to open at 11psi and completely open at 18psi. (Road Test) Boost was dropping off at 16psi on a third gear pull. Now can anyone tell me why the wastegate is even part of the system? My thoughts are with the wastegate closed at all times; I would be getting full spin on the turbo at all times. Then I could regulate the boost pressure with the blowoff valve.

It's not a blowoff valve, it's a bypass valve. You should rethink how this system operates in regards to it's bypass system.
Not going to try to explain the "why" of why you shouldn't consider welding the wastegate closed.

The adjustment of the rod is a temporary fix, as the computer will relearn back to stock specs. You haven't read the OBD2 codes, as was advised in your other thread?

You can do anything you want to. But; why do you think they would spend the money on redundant parts? Engineers don't normally add extra stuff for no reason.

P0299

The way I see it! The boost will push the bypass plunger open, when the psi gets to the maximum allowed. The bypass plunger also is sucked open with vacuum, when the throttle is closed, and the engine creates max vacuum. The only logical reason for the wastegate in my opinion would be to slow down the spin to prevent the amount of air diverted to the exhaust. And maybe to lengthen the life of the turbo. Can any give me a valid reason why me thinking is not substantial.

P0299 is a code for underboost. One member reported that his was caused by a boost leak, specifically one of the charge pipes was split. There is a link to a homemade boost leak tester somewhere, I think it's in the how-to for engine leak down test. I'm on my phone or I'd post the link for you.

You can search here with the search window at the top of every page, That's p zero 299. It may also have to do with the bypass valve. The diaphragm could be split or the spring broken. It's not terribly difficult to remove the cover and inspect it. Or it may be the bypass solenoid, mounted on the intake manifold.

I found the link for the homemade boost leak tester. 2.0 LNF Engine Boost leak test a stock SS LNF. - Cobalt SS Network

I don't think the wastegate and the bypass valve are redundant. I think the bypass valve diverts incoming boost pressure to the exhaust when you let off the throttle, reducing or even eliminating flutter. The wastegate diverts exhausting boost pressure, not allowing it to spin the turbo, when you reach maximum torque, so you don't blow the engine up.

Do yourself a favor, don't mess with the wastegate, except to put the adjustment rod back where it was. Underboost rarely has anything to do with the wastegate on these vehicles.

Over paid engineers! They don't know what they are doing. Why not just attach a hairdryer to the Throttle body?

Now that's sarcasm.

Wastegates

When a turbocharger’s exhaust-driven turbine wheel spins fast enough to produce the desired level of boost, a wastegate is typically used to allow the excess exhaust pressure to divert around the turbine wheel. By opening the wastegate (typically boost-pressure referenced), exhaust pressure bypasses the turbo’s turbine wheel to prevent the turbo from reaching an unsafe speed. You’ll find external wastegates on the exhaust (hot) side of turbo plumbing between the turbocharger turbine wheel and the exhaust manifold—or sometimes in the exhaust manifold itself—where it can get exhaust upstream of the turbo and route it back into the exhaust downstream of the turbo. Not all turbocharger systems need wastegates, such as late-model turbos with variable-geometry turbine housings (which can provide similar capability).

In its at-rest state, a wastegate is closed and boost pressure can be controlled by varying the pressure of the spring holding it closed. A wastegate can also work in concert with a boost controller to improve boost response by staying closed to a higher boost threshold.

Blow-Off Valves

Located on the pressurized intake (cold) side of the turbo plumbing, blow-off valves (BOVs), like wastegates, are normally closed and open to bleed off boost pressure. Their main job is to prevent the pressure in the intake tract from backing up and causing compressor surge when engine speed changes abruptly—like when the throttle closes during a shift. When a BOV is vented to atmosphere, it produces a distinctive hissing sound, and when a BOV isn’t used or is of insufficient size, the compressor surges and makes a chirping or rattling sound. Compressor surge can put stress on the compressor and its bearings, shortening its life.

Like RJ suggests Do yourself a favor, don't mess with the wastegate, or your gonna have more problems than you have now.