I had my boss 302 ported by him for my s197 over the winter and as far as quality goes he really does a good job smoothing out the runners and getting rid of the fins at the inlet. As far as power gains, i cant say as my car is still in storage and i havent been tuned yet. Surprised you arent going with a ported 18 as the boss 302 wont fit under the stock of an s550 without modifications. Also the ported 18 has a slight edge over the boss 302 IMO