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precat or downpipe

  1. Has anyone ever hollowed out the pre-cat/downpipe for more power on the 1.8?

    Volkswagen Passat B5 Discussion
    This was done on my Audi A6 2.7T, but they looked like they were easier to do? The shape of the 1.8 pre-cat looks problematic. I understand there is an O2 sensor relocation neccessity when doing this. Is that true?