not building boost, am i missing something? Options

[easternpiro1]

Hi all, was wondering if i can get some feedback on something i was missing. here's the story:

recently a friend and I fixed a leak due to stripped thread in the head causing a leak between the exhaust manifold and block.

after rethreading and putting everything back togehter leak is gone BUT now im seeing much lower boost numbers after taking it for a drive.

I own an AEM tru boost controler/gauge and the boost is currently set to stock wastegate pressure (8psi) and consistently held this pressure PRIOR to fixing the exhaust leak.

as of today, my first drive out, my car would not pull past 5psi and touched 6psi BRIEFLY. I double checked my IC piping and adjusted and retightened.

when i went back out the car would only boost up to 4-5 psi adn sometimes as low as 2-3 max.



Im pretty sure its a leak somewhere but it can only be one place as the only IC piping that was removed was the piping coming from the turbo (charge side) i have checked and double checked it.

is there something im missing? any helpful hints would be appreciated! thanks!

[pitcelica]

Lagos is right on this one. The test you've done is useless. At free-revving, there isn't enough exhaust air flow to drive the turbine at a high enough RPM to build boost on the compressor side. Also, a turbo isn't a positive displacement pump. Unlike a roots supercharger where there is always the same volume of air forced into the supercharger, it's not because a compressor is doing a revolution that a certain amount of air will be force into the compressor outlet. It takes a lot of turbo RPM to build boost o the compressor outlet side.

I can't beleive you have not ruled out this problem yet. I'm not saying that you didn't try hard enough, you certainly did. But I'm sure you missed something really basic. A turbocharger isn't something that is really complicated. I suggest you to go back to the base. Do a boost pressure test from the turbo compressor. Be sure to block off the IAC inlet. Verify that you can get at least 30 PSI in this test.

The other test is to verify that the wastegate stay shut and that all the exhaust airflow actually pass through the turbine.

Then, physically verify that turning the turbine result into a compressor revolution and make sure that the shaft is turning freely. Verify that the turbine wheel is in OK shape (no bent/broken blades).

If all those points are ruled out, there is no physical reason for this turbo to not boost.

Are you sure your boost gauge is accurate and correctly connected to the intake manifold. It should read about -19 inHG at idle, 0 psi when the engine is off. Verify if it is correctly displaying a boost event using a mityvac or compressed air (be sure to use a pressure regulator and set it at around 25 PSI).

Do not give up!

Sam