'93 Merc Sable modifications and aftermarket

My son and I are looking to modify the ole sable and looking for people who can recommend upgrades that they have installed. As we live near Toronto, Canada, we do not get they same exposure to upgrades. Currenty, I am looking at a new exhaust system and would like to go low resriction or dual. I currently had a set of unique SHO rims and slightly wider tire. I previously had 225/55/16 tires but will move to 225/50/16 for the next. But for now we are looking at exhaust.

Please send all suggestions.

Thanks,

MartyB