Building an Expansion Chamber

well like i said not exactly to his spec but bear in mind this is a 48cc also added a before pic that shows the size a bit better
 
Before the belly stinger, was it just a hole in the end of the cone? From what I've found, the resistance of gas flow through the stinger is what controls the pressure bleed off rate in the pipe, and therefore is very important. Some restriction is neccesary, but too much will choke the engine. The ideal amount is another variable that can be dialed in to make the pipe preform the best.

When I started, I used some 1/4 OD copper tubing that was far too restrictive. It was very quiet however. That was before the header was at a somewhat optimal length though, and it may be worth revisiting.

I ended up with a 12" piece of 3/8" black iron pipe, the stuff used for plumbing natural gas. It was the most appropriate thing I could find at the big box store, haha.

Later I welded the end shut and drilled four holes in the side of the tube. No difference, even in sound. This setup is pretty loud.

Keep in mind that the tube is only inside the chamber about 1". I figured due to the relatively large diameter it may disrupt the wave if I stuck it in all the way to the belly. Would likely be quieter though.


Currently my engine is all taken apart, I decided to man up and finish balancing the crank before revving the thing to the moon. It amazes me how tough the steel in the crank is, while the rest of the engine is soda cans. Took me a while to grind through it, with a cobalt bit to boot! Think I sharpened the bit after every couple minutes of drilling. JB weld is drying in the holes left behind. I filled in a couple more holes as well, I'm curious how raising the CCR will affect the engine. From what I've read, there could be no low end whatsoever left, but that's ok, jb weld isn't hardened steel. I'll grind some of it out if it's killed the torque.


Logan
 
While on the subject of building expansion chambers I suppose this would be a good time to show this effort. I made one two years ago with various silencer attachments and then went back to the 2012 Grubee 66 EPA stock exhaust. At the time there was not enough performance enhancement to justify its moonshine still look on my bike. The engine was always a wimp on hills seeming to lose half its power at the time you were hoping for twice as much. A recent change to a cheap Dellorto clone did help some, but it's uphill tendency to go into a four stroking blubbering behavior was still there. Since the original installation, the bike has a iridium spark plug and Opti-2 two cycle lube which seems to run cleaner in the absence of any catalytic converter action that the stock muffler may have had. In a recent test, replacing the stock muffler with the expansion chamber built to Jaguar specs (for the most part) has made the desired improvement to the uphill performance of this mostly stock engine. The engine will pull through the hills without going into any noticeable four stroking like behavior.

003.JPG



001.JPG


The exhaust header and unwelded compression adapter are 1 inch thinwall electrical tubing standard with some plating removed so a local auto shop could weld the shape into the rough notched tubing. The expansion chamber is a 4 inch galavanized vent pipe from Menards; one piece that has been cut, shaped and pop riveted and held to the header with hose clamps. the expansion chamber was later coated with a high temperature sound deadener an covered with aluminum. The exhaust is out the belly with a garden hose standard brass fitting that allows testing silencer ideas. The bottom of the expansion chamber also has a hose standard fitting that allows testing of silencer ideas and also serve to clean and inspect if needed. In running the tests; the engine has that distinctive shrill expansion chamber sound I remember from back in the day. As pictured, there is no silencer with a sound level too high for urban road use.
 
i like it wolfshoes! hey it may look like crap but it worked , with stock exhaust im lucky to get 12mph or so going up a steep hill with the one i made get 22mph or more vast improvement even if it is noisy as hell , my wd40 can with beancan lid baffles worked very well for a while but eventually the lids fell out and then it fell off haha i think i'll try extending and expanding the stinger
 
the pipe of zippinaround looks skinny but maybe because his header is bigger than what I used. With my torque pipe design the outside diameter of the belly is only 53mm for the 49cc and 58mm for the 66/80cc
 
it may have not printed the pieces properly or something but i did get the pulse rate program and entered measurements you gave it does work anyway thats the main thing , yes i made it from bits of an old barbeque bt i measured the centre of belly its 44.25mm
 
Wolfshoes, it does appear that the expansion chamber increases fuel flow and therefore corrects stock jetting or makes it run too lean. What performance differences were there between silencer types?

Today I got the engine put back together and tuned in. The crank balance is not perfect, but vibration is much improved and I'm not afraid to do top speed runs now. The jetting was not a precise art, I have a set of micro drills that are all jumbled up so I measure them with a caliper. The size I ended up with was .031. It ran a tad rich, but taking the stock airbox off took it back to ideal. The engine did not rev any higher though. When I had it apart, the case got somewhat stuffed (which I though would boost high rpm power and increase revs), and I raised the exhaust port a tad and evened it out a whole lot. Low end seems to be a tad diminished, especially after heating up a good amount. Would the increased CCR limit revs or power? I shortened the header another inch or so but it was too dark to go for a spirited ride. Slow ride was inconclusive.

Back on topic. Zippinaround, what is your gearing/revs/limiting factor to your engine? It seems like you should be getting a higher top speed with an expansion chamber. Or is the pipe's powerband just tuned to low revs? It looks like your header is on the longer side, so that may be the case.


Tomorrow this bike is gonna hit 40. I've done 38 on two occasions, both downhill lol. So far flat record is 35.5, on bike speedo that concurs with gps when I checked one time. Gotta fix the jeep at some point too... :)


Logan
 
the rest of my bike is totally stock except for plug and plug lead , record on flat was 30mph , but where i live is very hilly so i wanted power on hills theres not a lot of flat around here but the bike loves hills now and topspeed is roughly the same on flat (maybe a tad higher then before). back to everyone saying my pipe is skinny wayhey you were right hahah! seems its almost 10mm skinnier at belly , i will make a vid later so you guys can hear its roar!
 
So I just got another camera, but a little too late. I trued the crank with the bearings supported on steel 2"x2"x4" blocks and magnets to hold the bearings steady (Instead of vee blocks). Checked it with a dial indicator and whacked it with a brass hammer to true it. I filled the case sides with about 1mm of liquid JB Weld and stuffed the bearing bosses with putty JB Weld using a Teflon Tape cover as a mould. Here is Jag's photo of where to fill:

cranks2.png


So I also:
filled the flat area on both halves with 1mm of epoxy to reduce side clearance.
filled the transfer recess up as high as the crank cheeks.
drilled oil breathe holes to let oil flow through the bearings (there was signs of stagnant oil).
put the seals in backwards to take up more volume.

I hope Jag forgives me for this crude alteration to his print,
Red is where epoxy was added, blue is where metal cut off.

full


Steve
 
Back
Top