I'm new with the cougar, but not with a V6 car fitted with an ATX. With any N/A car, you need a certain amount of back pressure to get the engine to rev, then in the high end, getting rid of back pressure is wonderful. In an ATX with a Low stall speed torque converter (TC), you are pretty much losing alot of low end torque, and in an ATX you need that. In an MTX or an ATX fitted with a High stall TC, you can revv the engine in neutral, and get the RPM's up before a launch, so now th low end torque isn't as important. But still needed. The VRIS system on my engine (don't know if you guys have it) intentionally builds back pressure in the intake manny with the use of butterflies(like in the TB). At a certain RPM, they open, and allow full flow through the intake manny. That back pressure allows the engine to build some low end torque. Am i making any sense here? I try hard to type in english, but often I don't. Many people will open up the intake, headers, and exhaust by adding larger pipes, but will leave the stock cat to keep some back pressure. But remember there is a max size where the piping will be too big, and therefore you will lose air velocity of the air into and out of the engine. If yout exhaust piping is too wide, you will actually cause a vacuum tyow effect where the air towards the end of the pipe has no velicity to get out, air can actually enter the exhaust pipes and flow in the wrong way, there for losing more power. If you have a Turbo or SC, then you want to remove alot of the backpressure, still keeping a little. If you are all NA you need some back pressure, or you better be getting a Turbo, SC, or upgrading your torque converter. Good luck.
Jeremy