Custom exhaust

trey johnson

New member
Has anyone ever put a pit bike exhaust on a gx390 and dyno it to see if it might would help performance and better sound.. I seen a video on the name was gx390 thunderkart and it has some sort of motorcycle, dirt bike, or 4 wheeler exhaust and it sounds awsome to me
 

kartboy63

Member
I thought I was the only one that ran a muffler, go to ten mile or bj's with a muffler and they look at you like you crazy, when it really does help you, over at them tracks there are some flatheads that sound like the meanest thing you ever herd and I go with mine that sounds like a tiller and they cant touch me
 

trey johnson

New member
Also can someone chime in on and tell me about how long a mild built exhaust on a 420cc predator motor is supposed to be.. I did a little research and I had no idea that an it's that much mathematics to building an exhaust so far I seen where it needs to be like 30in long and 32mm or bigger ID
 
Formulas are good, there are a lot of them, but they only get you close. Make it long, test, cut, test..................
 

trey johnson

New member
Make it long spray cheap paid to that will flake off find the burnt spot cut about 1in to 2in past burnt spot test again if all is correct then add muffler... could this technique be used in a modified motor build
 
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