What exhaust modifications make sense on a 4 stroke?

[Sgt. Howard]

I know next to nothing about 4 stroke modifications- I am thinking of a lake pipe or "Pooh-pooh" type pipe on a 4 stroke and wondering what harm it might cause- I am more interested in lowering the pitch (and possibly volume) of the engine as well as the 'eye candy' effect than performance, but certainly do not want to HARM performance. Any clues?

 

[curtisfox]

No set deal for 4 storke a lot of people say you need back pressure, but you don't. Any dragster or race car/bike is straight through. The only resin to use a muffler is to quiet it down, enclosed is a 212 power race bike were the pipe is stepped up bigger as it goes back. The bigger the pipe the deeper the tone.........Curt

 

[Sgt. Howard]

What frame is that? Is that a Worksman?

 

[curtisfox]

Ya! sportscarpat

 

[Steve Best]

Awesome bike Curtisfox!
My experience is with hotrodding Briggs is with my rototillers and mowers. Head mods, compression, porting, carbs, raising governed speed, exhaust and mufflers mainly. Curtis is right, no backpressure needed, but they will be too loud. Long head pipes tend to help low end torque (power at low rpm). He is also right about bigger pipe for deeper tone and his diagonal cut tip makes for a less sharp note. I made systems like Curtisfox pictured for my mowers and rototillers and they worked well even without a muffler. Deep mellow sound, aim it at the ground and it was acceptable to keeping neighbors. Even quieter was to narrow it back down and add any muffler to it.

I needed a muffler for my current motorcycle build. It had a muffler housing with no baffle or core. I built a baffle from 1/4" threaded rod with 5 fender washers at irregular intervals. First one is bent like a "V" to direct flow around. Works well.

 

[curtisfox]

Not mine, LOL Sportsman flyer Pat , just posted for exhaust picture. I am doing one but not posted yet, just to slow going now ........ Curt