Separate names with a comma.
Discussion in 'Motorized Bicycle General Discussion' started by xlite, Sep 17, 2009.
As am I, pleasantly surprised actually
How do you shorten the header? And what is the point of the springs on the headers? Also why did my exhaust come with all these random bolts and stuff?
The header is shortened by cutting the copper tube between the exhaust manifold and 45 degree coupler. The springs hold all the pieces together and allows easy adjustment of the header length. Pop the spring off, shorten the header, pop the spring back on and go test.
The extra hardware is for different mounting options.
ok got it, but how do you cut it lol? elmer scissors? lol, dont u have to get a perfect cut too?
The best way is with a plumbers pipe cutter, but you can use a dremel tool or a hack saw. Yes a good square cut will be nice to aid in sealing.
I now have about 600 miles on the pipe and it seems to be holding up really well. Here's a pic of the spring with stainless steel safety wire through the center.
You can now see that the ignition wires have more than enough clearance.
I have one of these pipes also. Question.....If need be, can I cut the tube (pipe) with the loop in it in order to tuck the chamber up under the bike or will that effect the tuning of the pipe? As it is now the chamber hangs way too low.
Changing length WILL effect tuning. Generally shorter moves the band toward higher RPM. For better or worse or how much who knows.
owners of sbp tuned pipes,
How long is your adjustable section of the pipe and where do you feel the greatest power increase?
Hmm, I was mostly concerned with bike fit and felt my top end could use some help anyway so I just chopped it right down lol. I've always been pleased with my bike's lower mid range and to be honest while the shorting the length of the head pipe may focus the tuning towards the top end - there is still effect through the full range with this pipe.
While it didn't make it do wheelies or anythin' - my low end did improve a little too I'm very happy with it despite it's somewhat odd look. I'm very pleased with the routing options it allowed me and being able to have it end behind me and not right under my feets
BTW - the primary reason for spring-clamp exhaust is to isolate the exhaust system from engine vibration. Not uncommon to see on other small 2-strokes like snowmobiles, ultralights and others. It's usually a ball and socket joint - but with longer exhausts and high vibration the metal can fatigue and crack over time, particularly if unsupported.
any numbers? Inches of header pipe, speed/rpm of power increase?
Well, as I said I was less concerned with the "custom" tuning of the pipe than I was with getting it to mount securely and routed where I wanted it - But I'd say I took perhaps an inch off the elbow and 1/2" of the long J pipe.
The exact performance increase for my 66cc 44t is difficult to tell you as it was mostly acceleration, my 0-30 improved noticeably. After I readjusted my fuel-air mix to compensate it ran better on this pipe too.
Unfortunately I didn't set up a 1/4 mile drag run (1/8 mile? lol) in retrospect I kinda wish I had. With a buddy and a stopwatch I could prolly figure the acceleration difference. I do have an almost perfect 1/8th mile section on my way to work - but w/o that stopwatch all I can tell you is I picked up a healthy 2mph.
This doesn't accurately reflect how fast I got to my top speed though...
It may not sound like much - but little will effect the top speed of my bike, with the 44t @ 33mph I feel it's close to redline. Yet acceleration is more what I'm interested in anyway. I will say it's not a "peaky" powerband - it's well spread and usable.
lol - I hope someone does break out a stopwatch for a "before and after" but sadly - I haven't even someone to race. I'm the only MB around here and the local mopeds are a far too easy prey
I learned that 40 years ago building exhausts while converting snowmobile engines for aircraft use. "Loosey Goosey" and "Flexy Wexy" is the key. SBP recommends against welding the copper joints for just that reason.
That's why I think a lot of these guys who are just welding up pipes are barking up the wrong tree.
Well, with a hard-mounted engine (no rubber flex) and a well designed and mounted exhaust there prolly isn't much to worry about, the stock one just hangin' out there vibrating like a tuning fork prolly isn't the best though heh
While the spring mounts are superior - they can be a pain and I wouldn't want to discourage the DIYers, yet I would like to see a combination of the two.
I haven't seen dirt bikes with spring clamps and our ultralights had FAR more torque and flex than these MBs... I'm still glad I have those springs tho, my buddy wrecked my bike and even though it cartwheeled I had absolutely no damage to the exhaust - had it been hard-mounted I bet I wouldn't have been as lucky.
One of the things I love about these machines is the diversity and the sheer multitude of different ideas, I wanna see more DIY jobs lol
Installed SBP expansion chamber pipe today on a 69cc. Noticable
low end torque and mid to high range. I am not sure whether or not
to adjust header tube joint, seems to be doing good the length it is at.
Plug is a nice chocolate-tan color. Pleased with the easy installation and
I ended up taking a 1/4 inch off the straight copper tube
for tuning. That made a more noticable differance running
wise. Unfortunately the surrounding neighborhood called
the police on me. The town has a very low tolerance on
anything that sounds like a dirt bike and skate boards on
the street get summons to appear in court. So in the area
I live in, I will have to go back to the stock pipe. The tuned pipe drawed to
much attention. I saw the three squad cars in time and turned the
engine off and peddled home without being pulled over.
Aww, that sux...
You could try this;
Just about a foot of high-temp rubber hose stuck on the end to keep the exhaust from spewin' on my pack/kickstand, it took the edge off the "bang" sound and may help - cheap mod too! It had no effect on backpressure ofc - but if yer willing to shave just a touch off yer performance you could get one of those lawnmower muffler cans as a "tip silencer"...
I havn't done this yet - but I'm gonna drill out the pop rivets and investigate inside the polished aluminum section... I'm betting there's no wadding in there, thinkin' bout making it a "glasspack" of sorts.
There should be a little wadding in there. I took mine apart and put some more in, though! Pretty easy.
Charged - is that with or with out the extra muffler?
Nice - thanks for the tip Pablo
how long is the stock copper tube?