As most of you said above you need decent mufflers/resisnators,simple but a bit of effort.Ive built many huge straight through systems for fast street cars and race cars,which have passed noise tests.The key is to make them as long as possible,and as many as you can fit.Mufflers fitted in different positions in your exhaust will work at different rpms,so more will work over a wider span of rpms(this is a science).Turbo cars are easier because the turbo actually works as a muffler as well.No offence but CANONS are a joke!!!Also stainless systems are always a few DBs louder.If mufflers arent straight through then you will loose power,simple as that.Have you noticed that any decent race car has custom built ones?Thats because you cant really buy anything decent,again no offence but true.Also notice with most of the off the shelf stainless canon type mufflers,they drone in your ear when cruising,drive you mad on a long trip.My Dad and I build proper mufflers all the time but im not here to make money so if you can weld I can show you how its done.We also build Active exhaust systems which are legal,but thats another whole story!!Good luck,cheers Matt