SINGLE WALL OR DUAL WALL EXHAUST; IS THERE ANY ACTUAL DIFFERENCE OTHER THAN THE LOOK?

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A FRIEND TELLS ME THE DUAL IS MORE RESTRICTIVE..... THIS DOSENT SOUND RIGHT TO ME. ANYONE OUT THERE KNOW IF THERE IS A DIFFERENCE IN PERFORMANCE OR IS IT JUST COSMETIC?

 

there's no difference in the tips... the dual wall might be a tad bit quieter than the single, but nothing very noticeable.
-GP-

 

pretty sure its only for looks

 

No difference performance & sound wise.

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Thanks for the input.