That one is 58-60% of the head pipe, according to Graham Bell and Gordon Jennings that’s about ideal. That bike is as fast as a lot of 66-69cc bikes, it actually hits the power band at around 6000rpm, it will turn 8400 rpm before the ignition flattens out.
Exhaust What did I do? TLAR exhaust mod?
- Thread starter Urban Fatbiker
- Start date
What I did was add a pipe with a smaller stinger to create back pressure, if you look at all of the eBay-Amazon pipes they are all made wrong in my findings, the stinger is as large or larger than the head pipe.
Chainlube
Well-Known Member
If you have a 1" OD header, then a 5/8" Id stinger will be right around there. What's the OD of your header, right off the head?
Urban Fatbiker
Well-Known Member
In my avatar, the grey bottle is fuel too.
But then, the engine was on the back.
Its not there anymore.
Damn.
My pipe is close to 7/8”, the stinger on the silencer is a little less than 5/8”. It’s odd that the factories keep making the pipes with this flaw, I know we’re not the first people to find their error.
Chainlube
Well-Known Member
That's weird, the stinger portion coming out of the expansion chamber looks to be the same diameter.
A good idea for a nice quiet pipe is to lop that factory stinger off, leave an inch sticking out, slice into the left over stinger making 1/4s. Get a piece of 3/4 OD seamless, slip inside the expansion chamber as far as it will go, pinch it and check how far it goes in. Don't want it to go past half way. Once the location is found, then find the angle out the back and task it in place. Use a band clamp to squeeze the end in on the new stringer and weld 'er up. Leave it a long until the silencer location is determined, I guess some place past the seat post.
Doing that makes a belly stinger, which has more low end and is quieter than stock.
I'll get Stan to send me down one to experiment with and then revisit this thread.
Chainlube
Well-Known Member
This is the pipe I bought, For me it's $100 experiment.
Urban Fatbiker
Well-Known Member
When I was reading on this a few months ago, I understood that would improve the power band response at higher RPM.
I'd be curious how it affects low RPM as well. I think with a shifter, and a trail rider, I spend more time in mid and lower bands than a single sprocket street runner?
Chainlube
Well-Known Member
We'll see how it all plays out, probably get it later in the week. I'm going to mount it on my mountain bike and try it unmodified first, then try with the belly stinger and no silencer, then with a silencer.
I bought the black one so I can just hit it with some HT paint when I'm done welding, of course when the stinger gets modified there's no turning back.
If it's anything like the 4X bike it should be OK.
I have that pipe on my 49mm bore engine, as is it will wake up the dead! I added a silencer to it also.This is the pipe I bought, For me it's $100 experiment.
