it's a y pipe connected to the exhaust. (i imagine connected at the downpipe) that has a flange with an electronically controlled "butterfly". You can connect it to a flip switch or even the AEM/EMS. My only gripe with the electric ones that it takes a while to open if you wanted to hook it up to open at certain rpms/boost via AEM EMS.



Another option for a cutout that I've seen recently available is a boost activated cutout that opens very fast. It uses a wastegate type of actuator that's boost activated. A "Supra" performance shop "Sound Performance" started manufacturing these this year. I'm thinking about getting one if my new exhaust is too restrictive (which I doubt). check it out:

 

SP cut out in action:

http://www.youtube.com/watch?v=C556EHYUijA

cutout thread from supraforums.com

 

Ideally, take your car to the tuner and have the switch also toggle the nitrous map function in the EMS. Since the cut-out makes changes in the air-flow characteristics, you would want to atleast optimize both fuel and ignition tables to compensate.

Essentially you will be running open header and the AFR curve should lean out as a result.

-asura

 

That supra cutout looks really cool. I could go back to stock exhaust and be loud as hell when I wanted with more powa!