batman
Serious Thumper
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SuzukiSavage.com Rocks!
Posts: 3806
osceola new york
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Your friend may find a few guide lines handy, a header pipe larger than 1 1/2 " is too big and even one that size is only used on motors with increased displacement and after market cam (not stock) header length for a 650 cc bike should fall between 30"to 34" (stock is 32") longer favors lower RPM , shorter favors higher .If his design doesn't fall between these guide lines your bike may run worse, if the header pipe is to large ,speed/and temperture of the exhaust gas slows killing any chance of making hp, and you need a muffler to create back pressure.Our header is double layered which keeps the gases from cooling( slowing down) a single layer pipe would need to be made shorter.The exhaust passage in our head is of bad design ,not like most other bikes, I hope your friend knows his stuff. Many on this sight with stock motors have found that using a H-D Dyna muffler ,carb needle mod/rejet,and less restrictive air filter ,to be the route to a smoother and better running motor( 1-2 more hp) for less than $100 .
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