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Minimum wastegate pressure.

Practical Reflash Tuning

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Hey guys, I have a question about minimum boost pressure.

I have a USDM 2005 Subaru Impreza STi. I am trying to re-tune her for added components and also correct some of the crap from a previous owner. The car has the factory VF39 turbo fitted and I was wondering if anyone happens to know what the minimum wastegate pressure is or how I can find out. The factory VF39 is internally gated so the spring is non-serviceable. Thanks in advance.

whats up man i have a bugeye with a vf48 and Im pretty sure there both vary similar to each other and i know mine is about 11 or 12 psi.. Hope that helps

Hi Starryboar, you probably have your answer by now but for anyone reading this thread I thought this might help.

Here is a quote form COBB's "Accesstuner Subaru Tuning Guide" that is referencing Boost Creep and in it they refer to the wastegate boost pressure.

"From the factory, most all Subaru factory turbochargers are equipped with 7-10psi wastegate actuators, meaning the mechanical minimum for boost pressure is 7-10psi when input energy is enough to create that much (or more) boost. While this is also a minimum, it is expected to also set the cap for maximum boost levels generated when the boost control system is disabled. The internal wastegate port area of the turbocharger is engineered to provide adequate flow with stock exhaust systems at stock power levels while keeping spool-up quick and predictable. A significant limitation of this wastegate area is encountered with the greatly increased coldside and hotside airflow capabilities through the turbocharger that are created by upgraded downpipes, catback exhausts, intake systems, etc. By definition, mechanical boost creep is the forceful overrunning of the turbocharger due to the wastegate's inability to relieve exhaust gases from the turbine housing – without a complimentary increase in airflow through the wastegate area, it is unable to relieve/bypass enough exhaust gasses to keep boost levels limited to the actuator’s spring pressure."

If you simply unplug the boost solenoid you will run on the wastegate spring pressure. That's the easiest way to validate the exact pressure since this will vary depending on modifications like intake and exhaust.

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