Expansion Chamber

Yes, I pulled my engine off the bike, pulled it down removing the exhaust manifold (it has one) in order to get the measurements of the exhaust port which is rectangular. From there I pulled the carb and plug off and used a mini maglite to see the transfer port opening on the cylinder and rotate the crank thru from opening to close of the ports. Likewise the exhaust the same way.....

I got the specs for my Tanaka Free Spirit recently and found the rpm for max torque and hp and maximum RPM. Just don't know first hand the exhaust temperature at operating speed.

You can see what I posted here. The Java software I used is less than what I would like to design with and then go to the bench to make. It was fun playing with it on paper though.

If anyone wants to see it it's here.

another home made pipe

hey there dave :-)
I did pretty well did gut the muffler (cut off the tube on the lower piece
the first one was larger & I will probably make a better one or buy a better one & adapt it
take care
JAK

this is the one I did tonight
I think 3 times is a charm
this muffler may be loud though
take care
JAK

Attached Thumbnails

 

Jak that is looking pretty good. I have to give it to you for persistence, and welding skills. The long center section, the portion that just carries the wave is designed for a slow revving engine, I know you knew that. The first cone amplifies the sound wave the last cone drives it back and shoves the fuel that escaped the port back, acting like a supercharger. The way you tune a pipe is to calculate the speed of sound, and then time it to return to the port at the speed you need it. That looks like a 5hp Briggs muffler, I don't know if that will work it has a block 1/2 way through, all the stingers we used to put on were straight and the length has an affect on the tune of the pipe also. Good work keep it up. Have fun, Dave

PS: If I were guessing at the size of the stinger you need, I would say 1/2 id. and 6" long to start with. You can use a two stroke muffler that emulates those dimensions.

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Chuck - The monkey has the spark plug again!

hey thanks for the kind words
I have no shortage of mandrel bends here & make the cones by cutting triangles out of pieces of exhaust pipe with my chop saw
I did use more of a stinger on the back this time the tube diameter inside is 5/8 & is pinched almost shut in the middle with holes drilled on either side of the restriction the outer diameter is 2.25 this is a bit better then the briggs one because probably 30% of the exhaust gasses can still pass through the pinch & I can tune it by pounding a large screwdriver through the pinch :-)
Ill keep messing with it :-)
take care
JAK

Jak - You may have seen this, but this is the coolest thing I ever saw. I wish they had computers and animation in my day, I am kinda the guy that needed the visual on everything. LOL. Have fun, Dave
Two Stroke motor - an overview

PS: I don't know why but we used to trim the stinger at different lengths and change the power. If we got it too short we would weld the piece back on.

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Chuck - The monkey has the spark plug again!

I spent more time on the pipe today
I lenthened the first cone & shortened the second cone, shortened the center section also made the outlet smaller than the inlet
I put on a stock muffler
the result is that the engine really woke up particularly higher in the revs
I think I nailed it this time
with the last one it got terrible fuel milage & was slugish, I think that the center section was too long & that the cones werent different enough
it pulls rite where I want it too not too high but at a good RPM for speed & probably some climbing
Ill get a pic up when I can
Im also going to look for a nicer muffler
take care
JAK

Jak I don't know if you are up to it, but if you are willing to do the ports and take advantage of the scavenging that pipe is made to do, you will get a real head turner. I can't remember who it was that used my porting and the pipe, he also has the shift kit, said he can pop wheelies. Look over in engine mods for porting. Have fun, Dave

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Chuck - The monkey has the spark plug again!

yeah I did that :-)
lowered & widened the intake side & verry slightly raised the exhaust port & widened it
everything is gasket matched
as it turns out though the case from the engine that I just put together got screwed up when the main bearing failed
so the engine is noisy & you can take the magneto rotor & move it up & down :-(
I have another assembled bottom end which I took apart. cleaned out & inspected that Ill switch out today
the cylinder is niceley broken in allready
take care
JAK
I also raise the compression
it helps allot thruout the RPM range

OK did you lower the intake also? about 1/4 not more, I can never remember who asked these questions. LOL. The intake is a big one. Have fun, Dave

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Chuck - The monkey has the spark plug again!