OK - I'm thinking out loud !!!
I have spent the morning with my Cobra dreaming of the parts I need. My mind turned to the exhaust system and how to accomplish registration and yet have the side pipes I want. A light bulb went on and I had a thought!
I can not find any other reference this my idea so it maybe original. I'm posting to see how practical this theory is?
So, at the end of the extractors I'll run an exhaust system done through the chassis and out the back. ( this is simple enough and complies with the ADR ) However where the pipe bends after joining the extractors I want to put in a "Y" join and also run out of the car into side pipes. So At this stage after the extractor join and at the "Y" joint have a butterfly inserted so I can switch between the two systems.
Have the side pipes and internal exhaust set up with the same back pressure etc so the engine management runs and have either manual or an electric switching system.
In theory then if I want a quiet drive I would run the internal exhaust ( say in town ) and when out on the open road on just having fun turn the butterfly and run through the side pipes.
Well, what do you all think, shoot me down in flames or is it so simple that it took my simple mind to come up with it.