modified stock mufflers

jibco520

Member
Any of you guys with dynos ever fool with gutting, adding holes to a stock muffler and comparing to a header on dyno? I'm wondering what hp might be left on the table on a 12-14 h.p. or so build [mini bike].
Thanks
 
If you are talking about a stock predator muffler. You don't need a dyno. Just listen. The loudest engines win the races.
Anytime you can get more flow in or out of an engine hp will pick up. But Mufflers are the weak link in a stock predator. They restrict the flow OUT of the engine. Which in turn limits the amount that can enter the engine.
 
Any of you guys with dynos ever fool with gutting, adding holes to a stock muffler and comparing to a header on dyno? I'm wondering what hp might be left on the table on a 12-14 h.p. or so build [mini bike].
Thanks
Turn it over and drill a few holes in through the parts you can get too.
 
I gutted and built my own predator stock mufflers to run in some classes where we race. They picked up 2.5-3hp on my Dyno on my engines. Tried about 3 different sizes no matter what I did 3hp was most I was able to get out of one.
 
Yes our track just started the Box Stock class. There is one in particular I am going to watch. It sounds much stronger than the rest of us on the grid. With that screen on there doesn't seem like it would so much good to drill holes. Seems like that screen would stock anything.
 
Yes our track just started the Box Stock class. There is one in particular I am going to watch. It sounds much stronger than the rest of us on the grid. With that screen on there doesn't seem like it would so much good to drill holes. Seems like that screen would stock anything.

That screen doesn't really stop much. You can also modify it as well. But no matter what if the stock exhaust is modified properly then it will give more HP reguardless. Now how much depends on what you do to it and what's done to the rest of the engine. The screen serves as like a silencer of sorts, quiets it down more than anything instead of letting it full blast.
 
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