Hi C,
The JMB ones are non-tuned silencers. Size is really not as important as it is on the tuned setups like the KS, but as Dick pointed out, you want to go with the biggest ones as you want the engine to breath. It also lets those exaust cycles expand more which will help to reduce noise further which is the main reason for instanlling them in the first place. The KS setups give you some boost...up to 300 r's on the canisters and more with the tuned pipes. For the aerobats the canisters are best as they don't have that ramp in the midrange when properly setup. The tuned pipes (baseball bats hehe ) give a bunch more boost, but at the expense of some manageability on the throttle. The 'full' pipes as they are sometimes called really are best suited for racing as the boost is high, and they are very long. I really like the KS setups as they give that little bit of edge as far as power and yet are still very quiet. I saw the JMB cans at the Nall and they are very nice also. It looks like Dick may be getting a little boost out of his setup on the 210 as he says it's kicking more out on the cans than straight out into the air. Kinda interesting on a non-tuned setup. He may have hit the perfect length with that setup and is getting some resonance in the pipe. He IS good at setting these up you know!