Sound comes from the internals and not the shell material. All manufacturers I have spoken to verify this. Here's a bit taken right off the Two Brothers website:
"We offer three distinct canister shapes to choose from; C2 (small oval), C4 (traditional round 4.5” diameter) and C5 (large oval). All of the canisters perform and sound the same because all of the canisters feature the same 2.25" Stainless Steel Spiral Power Core. The core is what controls the power and sound, not the shape or material of the canister. The canisters are simply different styles. They all incorporate our exclusive technology and premium construction material. The different exterior shapes allows you to choose the one that best fits the style of your motorcycle. For instance most people prefer the C2 (small oval) with smaller sized motorcycles (like 600cc machines) while others prefer the C5 (large oval) with larger sized motorcycles (like 750cc or 1000cc machines). For those who prefer round canisters we offer the C4 (round)."
They are going one step further, in saying that size AND shell material don't alter the sound, it's the internals (packing and design of the core)... which is why Hindles sound different than Akrapovics which sound different than Yoshimura. Each brand has their own unique sound, and some brands offer different sounds (eg/ Yosh has a RACE can and a ZYCLONE or street-legal can)...
Rejetting can get you something, it depends on how the jet kit is installed and how well your carbs are in sink. I installed my jet kit to give me more top end, I gained topend but lost a little low end so I geared the bike down 1 tooth. With my current setup so far no 600 has ever beat me on topend. I installed my that way on purpose, you can use diffent jets where you dont lose low end. I have done 3 6r jet kits and all 3 people love the differnce. I would do it again.
SacCity, is it running rough at all anywhere in the powerband right now? Any stutters at low rpm? Ever stall on you? Abnormal carbon deposit on the tailpiece of the can? Minor "bogging" at any part of the rpm range? Those are more serious signs, but a dyno can even detect more minor signs and help you find the proper setup for tweaking with a jet kit.
If it's running perfect in your mind, I don't think I'd bother.
"Keep yer feet on the pegs and your right hand cranked."
Q. Do I have to rejet my bike?
A. Yoshimura recommends that you rejet your carburetors or remap your EFI anytime a full exhaust system is installed on your sportbike. With slip-ons, it may not be necessary to purchase a jetting kit per-se, but it is important to at least adjust the pilot mixture screws and shim the needles 0.5-1.0mm.
Bikes are designed to work as a whole so if you modify anything all the rest has to be modified accordingly.
In my opinion you will only get more noise and no improvement in power if you don't jet the bike.
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