Ok guys i wanna know a little sum sum about this car....remember i'm learning, so when i buy my new STI can you take out the catalic converter out and run it straight through? And the turbo blow off valve how do i make it sound cool? 8)
Please post questions like these in the appropriate forum....
Cats....it's always illegal to remove cats unless you are racing off road. That being said, many people find excellent benefits from replacing the uppipe with one that does not have the light off cat in place. This allows for much faster spool up.
Besides that....many people say the other 2 cats don't cause any real backpressure issues until you are in the 450-500 hp range.
And BOVs...there have been discussions about this in great detail on other sites and there is a thread that has a good deal of discussion about it in the performance forum here.
Bottom line on BOVs......you'll kill performance if you vent to atmosphere with the way the ECU reads the MAFS. Remove the resonator in the intake tract and you should be able to hear the stock bypass valve just fine.