I had eliminate the down pipe cat and the other exhaust cat and it make a great diference in my car. Do you guys think tha if i eliminate also the uppipe cat the car will improve more or if it will no make a great diference??

 

removing the uppipe cat makes a difference adds a nice gain in power. Its safer too, because you won't get cat debri flying into your turbo.

 

I believe the up pipe makes the most difference out of removing the three cats!

 

I had heard from someone that the STi's factory up-pipe wasn't restrictive and didn't need to be removed.. Is that true??

 

I am not too sure on that one

 

The STi up pipe has no cat in it, but some say the heatshield welds come apart. If I had an STi, I would leave it be.

 

what size pipe does the STi have?