Every setup seems to be different. On the dyno my car had more hp and torque all the way through the powerband with the cutout OPEN. I also gained 20hp and 17 lb.ft of torque at the peak.

 

noticed the same thing here on my 96

 

I gained everywhere under the curve with my cutout open I have a 3"

 

the red line is my custom setup (almost like a loundmouth), the blue line is with a 3" cutout...HUGE DIFFERENCE at track and dyno

 

Does anyone know if you lose any power by having a closed cutout vs not having one installed at all? I usually leave mine open all the time but just wondering. I notice more power everywhere with it opened and it scares the crap outta people. Any dyno pics of this?

 

Mine was on a completely stock car after teh cat before the bend. 268/318 stock and 274/319 with it open.

 

Here is a pic from the dyno showing the difference with a cutout on my car. This is not a recent dyno sheet but I don't have any others on my computer, but you can see the difference on it. The first run (green) is with the cutout closed the other two are with it open.
Since adding more mods, the difference is even greater now.
http://memimage.cardomain.net/member...58_25_full.jpg