I ride Harleys and have learned a lot about exhaust from them as it is way more pronounced with only two cylinders. Straight open drag pipes mess with low end torque and jetting. a longer pipe with a small neckdown or baffle makes more power than wide open pipes. I,m sure cars respond the same. I have always run collector extensions and cut them off where they stop burning the paint.the motor benefits from a venturi effect as the gasses flow out and cool. So im in agreement with headers making more power if they are tuned properly with extensions.
