Parts will be here tomorrow early afternoon, today I'm removing the engine, removing the sprocket from the back wheel, adjusting the derailleur (which will be used until I find a 3 speed hub), replacing the tire and preparing the engine and bike for the shift kit and expansion chamber. I have a feeling that tomorrows going to be a really good day.
Thinking of ordering shift kit and exp. chamber, pros and cons?
- Thread starter rudyauction509
- Start date
I've read about a dozen threads on internal gear hubs and every one of them ends without any report of whether they work or not. Anyone with thousands of miles on a hub please let me know how they work!
Also I'd prefer a 5 or 7 speed hub if it'll work
Also I'd prefer a 5 or 7 speed hub if it'll work
from my experiance,and what i heard(from a very reliable source) i would go w/a derailer as they are bulletproof. and a 7 speed cassette and just shift thru the gears.it takes sum geting use to but in the end i am happier.
Finished build today, mixed results. Shift kit works great. Expansion chamber not so much. How restrictive is the muffler on the end? I got nearly identical performance with a stock pipe with end cap and baffles removed and the expansion chamber. Chamber gave me a tiny bit more top end, but not nearly what I'd expect. Any ideas before I go drill the end off the muffler?
I know these chambers are supposed to be great, and am confused by my results. I checked the spark plug, it runs rich with stock pipe and perfect with chamber, so why do I not get a powerband?
OK, I took a closer look at the chamber's muffler. It has no baffles, I could see the light I shined down the front of the chamber through the exhaust pipe, it's just a can full of insulation that absorbs the shock wave. Genius idea, and a very quiet exhaust! Still trying to figure out my lack of power.
Where the power band is depends on the length from the head to the banana piece.
How did you plumb your pipe?
None of these type pipes have baffles, but what they do have is a very small exit through the "silencer" and the tube that runs through the silencer is perforated and there is a fiberglass type packing around the exit tube, this is restrictive in itself, the only way to really increase flow is to cut the "silencer" off the chamber and weld on a larger exit stinger pipe.
The header pipe diameter is also critical for high rpm performance and the length as KC said will determine where the "power band" is ( what rpm the engine "comes on the pipe").
It seems most builders like a header pipe length between 9-12" I have mine at about 12-14" which isn't ideal for high rpms but the engine I have the SB pipe on wont turn high rpm's because its limited by an untrue crank that gets way to buzzy and limits rpm potential.
The SBP exhaust is good for better low end and mid range above a untouched stock exhaust, but if you open up a stock exhaust and get the flange port matched as good as possible to the exhaust port, the stock pipe will allow the engine to reach higher RPM's than the SPB pipe will, I know this for a fact since I have experimented with both on multiple engines and my fastest bike which hit 52 MPH did it with a stock type pipe that is gutted and has extra holes drilled through end cap.
The SPB pipe is an upgrade over a stock pipe for performance only if the stock pipe hasn't been modified for better flow, once the stock pipe is modified for better flow it will out perform the SBP pipe in the higher rpm range because it will allow the engine to rev higher because it is less restrictive than the long to small header pipe and the restrictive silencer that is on the end of all of the pocket bike type pipe which is what the SBP pipe is.
It's a good set up for low speed to medium speed builds that aren't looking for high rpm's.
Modify it with a larger shorter header pipe and cut that tiny exit pipe off and put a larger exit stinger on it and you'll probably have what you want, but it will never give good high rpm performance in it out of the box configuration, I had the same let down as you when I got mine and realized it was gonna add anything over what a modified stock exhaust would give me as far as high rpm, hig speed runs are concerned.
If you really want a pipe that will bring it to life, get on ebay and order a KX65 chamber and build a good flange for it, its a real expansion chamber that will perform, most of the pocket bike stuff is to small to work very good in my experience.
I set mine up for low end torque since I have the shift kit. The header is stock, as long as it was out of the box. I don't need high rpms, just better low and mid range since I have the shift kit. I'm heading out again for another test ride, I'll give it a second chance. If I still don't see improvements, I'll start gutting the silencer.
The rpm a pipe starts helping one of these engines isn't anything like a 2 smoker dirt bike, like a RM, YZ or KX
Mine aren't that noticeble either I can just tell a difference in sustained speed on a particuler hill and I notice if I pick up any mph on the top end, with these little engines belti g out a whole 2-3 HP when modified right big pulling power isnt seen with them in my experience.
When I say power band relating to these engi es I actually mean power increase and not a certain rpm where it kinda comes unscrewed and starts pulling like a mad man.....
I just find it odd that this motor cruised at 29mph and now cruises at 31mph with all of the upgrades. Shifting makes no difference to top speed, its like there's an invisible barrier keeping me below 31mph. I can only get about 35mph down hills. 5th through 7th gears hold within 1mph of each other on level ground. The rest lose top speed.
is this a on a 29er bike?
takes more power for the extra rotating mass but that may not really be your problem.
What mods do you have done to this engine?
compression boosted?
carb tuned to run without 4 stroking at cruise speed?
any port work done on jug?
Im sorry if Im asking questions that have been answered earlier, just trying to see what your set up is to know what you should have from it based on my own experiences.
takes more power for the extra rotating mass but that may not really be your problem.
What mods do you have done to this engine?
compression boosted?
carb tuned to run without 4 stroking at cruise speed?
any port work done on jug?
Im sorry if Im asking questions that have been answered earlier, just trying to see what your set up is to know what you should have from it based on my own experiences.
29", tires at 65psi
No mods other than shift kit and chamber
Regular slant head, extremely hard to start because of compression
Carb tuned for all speeds, carb chopped at 5, 15, 25 and 28mph, all between light and dark brown, never black or white. No 4-stroking except for a couple blocks when engine is cold.
No porting, how much difference would it make? I have the tools needed to port the cylinder.
Also would a couple small holes just before the silencer to allow more flow help or hurt? They help lots on stock pipes but not sure about chambers.
No mods other than shift kit and chamber
Regular slant head, extremely hard to start because of compression
Carb tuned for all speeds, carb chopped at 5, 15, 25 and 28mph, all between light and dark brown, never black or white. No 4-stroking except for a couple blocks when engine is cold.
No porting, how much difference would it make? I have the tools needed to port the cylinder.
Also would a couple small holes just before the silencer to allow more flow help or hurt? They help lots on stock pipes but not sure about chambers.
I'll also note that the pedals have a bit of resistance when coasting with clutch pulled. More than I'd expect but I don't think enough to hurt performance. Like 1/2 lb on pedal to turn the chains. All chains have a bit of slack, not overtightened or loose. Also all chains, bearings, etc. oiled with motorcycle chain lube.
On the smaller pipes ive found that drilling the rivets out that hold end cap on, removing packing and then drilling about 4-6 3/8" holes in the end cap to help the thing flow better will help performance.
Cleaning the ports up definitely makes a difference if the ports have burs and junk in them which 99% do
Cleaning the ports up definitely makes a difference if the ports have burs and junk in them which 99% do
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My bike seems to jump a bit when running 25+mph in gears 5-7, like the engine spins up a bit and takes up slack in the drivetrain, slows down a bit and lets slack build up and then repeats, about 2x per second. All chains are adjusted properly as noted earlier except the chain from the engine to the jackshaft, which is quite loose. I'm guessing to tighten that chain I'll need to make more shims. I don't mind the jumping, but could it be taking away any noticeable power?
If I remove the packing, will the muffler still be somewhat quiet?
If I remove the packing, will the muffler still be somewhat quiet?
it will be louder, you might start by just drilling rivets, remove packing, add some copper or stainless steel scouring pads for a looser packing and then maybe just drill one extra hole at time until you get the sounds level you want.
not sure what to think of the jerking....?????
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So should I assume that if I ditch the silencer I should get a bit more power than a stock gutted pipe?
at a particular rpm that could be the case, maybe a notice boost in lower to mid rpms possibly if the header length is allowing some of the exhaust to get fired back into combustion in those rpm ranges.
Im not expert on expansion chamber exhaust but I do know that to much restriction kills the grunt and the overall power through rpms of these little engines.
