Max, I have the 2 1/2 inch IPD sport exhaust and the Carsound performance CAT on my n/a '89 245 5-speed . I'm using a VX cam and the performance increase is quite noticable going from the OEM cat to the Carsound cat, very nice pick-up in the mid-high rpm range. I recommend it. I found that the system is very noisy with the full flowing rear turbo muffler, and that it needs just a little back pressure at the tailpipe, so I added a twin Monza resonator exhaust tip. This is a glass pack 2 x 2 1/2 inch tip that gives a nice throb as a performance motor should sound like, not the loud brash valve noise that is very apparent(ricer-like), especially on a wagon. It also gives a little better top end with the added back presssure on the n/a motor.
Don't do anything until you get the exhasut together, (plus K&N filter) you'll really like how the car behaves with the V-15 cam and the stock motor & 5-speed.
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon