davenew

The annoying resonance/rattle sound at 2800 rpm is gone. It's worth whatever hp I lose with not running the test pipes. The car feels just as fast but I've been working to much lately to do any logging.

Does APR code use the rear O2 sensors? I only replaced the front two when installing stage 3. While finally swapping the cats in the other day, I noticed the rear )2 sensors have some very heavy carbon buildup. Since the code doesn't throw a check engine light for test pipes, I assume the rear O2 output isn't used..

Leester

The rear 02s are still used, the software just ignores the cel request.

Hal_TT::CBP

as factory. If the cats are missing you will have a cat code/DTC per bank on the B1S2 and B2S2 sensors(working) but the CEL won't light. Readiness still sets, even w/o cats lol, that part is pretty cool in-itself, won't get you passed on an emissions VAG/OBDII check(DTCs) but if they don't pull codes the readiness will pass you, even w/o the cats.