When you gut the cat, you can SMELL the difference. Think of what a modern car's exhaust smells like and compare that to an old leaded fueled vehicle like early falcons, kingswoods, pre 86 stuff.

It sticks out like a sore thumb, the smell is so easy to distinguish, I can pick it every time when someone has straight through'ed their cat if I get a waft of the exhaust fumes.

Many cops know about this too, for the ones that dont, I wish they did. I'm not a greenie but the amount of harm a cat-less car does far outweighs the cost of manufacture as well as fitment of a high performance cat.

i found that when i got my highflow cat and exhaust it gives out the same bad smell as no cat, but your eyes don't burn and water when standing next to it while running like it does when there is no cat fitted.