Boost leak? Compressor bypass valve opening? We are not sure, but we aim to find out. We are experiencing fuel cut at manifold boost pressure levels that were less than before. Fuel cut occurs when the mass air flow meter reaches a higher value than the maps in the factory ECU think should be seen. Before we could reach 18.5 psi without hitting fuel cut, now we hit fuel cut around 17psi. These symptoms point to either a boost leak or a faulty blow off valve. Even with these issues fixed, the reality is that we don’t see how more than 310 to 320 wheel horsepower can be made on pump gas with the stock turbo in place.
Looking at the boost curves it’s already evident that the factory STi turbo doesn’t have the airflow to deliver past 5200rpm. It would be great to upsize the turbo to something that can hold boost pressure to 7000 rpm. We’ve started looking and we plan to let you know what we discover when we look at level two performance options. With a bigger turbo, we will address fuel and tuning issues once again.