Exhaust pipe

[Bikeuser]

I opened the exhaust pipe on my 70ccengine. i cant believe that there are so many baffles in this thing. I bet that i can get atleast another 3hp out of it with a proper tuned pipe. i am shooting for 7hp@7000rpm. it definitely looks like it was made to pass emissions rather than make power.

 

[jared3377]

Yeah, I recently did a muffler-mod by removin the baffle and drilling a couple of small holes into the baffle pipe about an inch or so from the exhaust tube. The acceleration and climbing-power improved, but the sound (of course) be came a little more throaty.

There's lots of threads about muffler-mods and tuned-pipes on MBc if you give a quick search, though. Good luck, and welcome to the site!

 

[Chuck L]

You can try siik mfg. to see if they have a pipe for 70cc application. I used a pipe from them that was made for a pocket rocket with a 49cc engine, I cut the pipe and and made it into a flat track style pipe, it comes out below the bottom bracket and points towards the left side of bike towards the rear wheel, I had to relocate kickstand to rear of bike. sounds good and runs good. Hope this helps.

 

[Bikeuser]

I was thinking about cutting down the length of the stinger. the long pipe that comes out of the end. that part limits the flow of exhaust gasses. since there are baffles and other obstructions in the large pipe. it will not perform as well as if everything inside was removed. china made it this way to pass epa requirements.
pull out the end and cut the stinger down to about 2" long. also i read that longer the pipe from the exhaust port to the expanded section the lower the range of rpm range the horsepower will occur in. I really do think that with a good custom made exhaust 10 hp is easy out of a 50cc engine and 13 out of mine.

I have not made these mods yet but I have wrapped the large exhaust pipe with a ceramic blanket. again the rpm ranges of these motors is defined by the speed of sound in the cavity of pipes. a higher speed of sound will result
this will alter the pressure waves that crash back into the engine. I will give a full report tomorrow on the experiment.

for a good read about 2 cycle exhaust google "2 cycle tuned exhaust"

 

[Jax Rhapsody]

I was told by a scooter repair guy that the hi-po exhaust pipes have baffling designed to suck the exhaust out, like putting an X-Pipe on your dual exhaust vehicle.

 

[Bikeuser]

But you also need a pressure wave coming back to act as a shield against fuel being purged out. the exhaust pipe that is stock is almost worthless for performance.

 

[Chuck L]

Dual Outlets

I hope I am not going aginst any rules by telling you this, I have done just what your thinking. Took pipe end off cut the out pipe in half drilled a hole next to other tip, well actually over just alittle bit so I could weld the the second tip all the way around painted black reinstalled.Don't have anyway to test for power increase but it dose seem to respond better especially through the powerband, It sounds better also. I don't know what the legal ramifications are all I know is it won't be going through any smog inspections. I guess you do at your own risk. Have fun

 

[Ghost0]

Bikeuser,
Try this thread.
http://www.motoredbikes.com/showthread.php?t=7800