You are correct, though in deleting both the side and center mufflers at the same time (and their corresponding factory mounting) we had to make bespoke exhaust support mounts to make this a viable option. By fumes do you mean exhaust flow? If so, closed routes through a smaller diameter tube before entering the center muffler. Valves open follows the primary flow path through the larger diameter piping. You can term this as straight pipes, though because both closed and open flow paths go through an expansion chamber in our center muffler bypass it has quite a reasonable cabin presence at cruising speed compared to any other "straight pipe" setup I've heard to date.

Here is a video so you can hear the difference in valves open and closed condition. It is more notable on the exterior of the car than the interior.

Sorry if I disturb. I am a little OT. I have the opposite problem. I want to replace my OEM center bypass to obtain max loud as possible.. Looking a used one to save money. My budget is under 1.000 $. GT3 Touring. I want to keep my OEM tips and valves.Maybe you can help me?
thks

There are a couple ones out there that reuse the OEM tips, sharkwerks notably. That said, there are none within your budget brand new, you'll have to find one on the used market and it is rare they drop in price to the mark you're looking for. However, make sure you pay attention when you buy a used one as there are different fitments for different generations on GT3s if I recall. If you change your mind and wouldn't mind replacing your OEM tips, I have six standard tip options for our center muffler bypass pipe and it is in your price point in new condition. If you want to do custom tips I can accommodate that as well.

I wrote sorry.