Honestly, I have no issue making a dedicated exhaust sub-forum. As long as it does not create more work for the moderators by doing so. Because we already know what is going to happen....
Someone is going to create an exhaust thread in tech. The thread is going to get moved to the exhaust forum. The user is going to bitch because he felt the thread should be tech.
Someone is going to create an exhaust thread in the Mustang Chat section. The thread is going to get moved to the exhaust forum. The user is going to bitch because he can't find his thread anymore (even though a redirect will have been left)
Someone is going to create an exhaust thread in the video section. The thread is going to get moved to the exhaust forum. The user is going to bitch because it was a video of what his new exhaust sounds like and it should be in the video section.
Someone is going to create an exhaust thread and put it in tech even though it isn't tech. He is going to put in the thread "I know this isn't tech, but not enough people visit the exhaust forum, I put it here to get more visibility, don't move it". It will get moved to the exhaust forum. The user is going to bitch and whine about it.
Someone is going to create an exhaust thread in the exhaust forum. Then they are going to duplicate the thread in the tech forum and the Mustang Chat forum. Again, their excuse is going to be the exhaust forum does not get enough traffic. Their duplicate threads will be deleted. They are going to be butthurt about it.
See a pattern forming here? We have been down this road before.