the pre-cats. You should be able to find a used pair of pre-cats, but, dude, SERIOUSLY, just use the aftermarket downpipes you apparently already have or get the downpipes from my other reply if you can afford them. Get the rest of the performance exhaust from that website link I put in my other reply. It's amazing! I hope others will chime in, but if your exhaust system is completely sealed up, air-tight, you shouldn't be able to smell exhaust fumes.