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Author Topic: "Quick Silver" M-BG 100cc  (Read 3114 times)
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Jonny Hotnuts
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« on: May 06, 2010, 02:42:36 PM »

Teammate and all around swell guy GEORGE MCMURRAY has put together a fine example of LSR engineering.
I have followed GMs build on this bike from the start and must say that I am really impressed.

The motor is a rotary valve 100cc Yamaha.
While George is not a forum member, he does read, if you have any questions or comments he will appreciate them.

(*these are just a few of the pics I have)













~JH



 
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Seldom Seen Slim
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« Reply #1 on: May 06, 2010, 03:20:27 PM »

Okay, I'll ask a question that I've never had answered.  It relates to this bike -- and to 2-strokes in general.

I understand the purpose of the expansion chamber in the exhaust - sorta.  I know why it flares from small to large as the exhaust travels through it -- but why does it need to be closed back down to small again at the exit?  What advantage derives from being restricted back down?

Thanks to all that answer me, and please don't make too much fun of me or I'll turn the curse-word filter up 'way too high on your posts!
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Jon E. Wennerberg
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DallasV
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« Reply #2 on: May 06, 2010, 03:36:05 PM »

Found this on the googletrons, I think it answers your question.

http://www.dansmc.com/EXHAUST_2.htm
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« Reply #3 on: May 06, 2010, 05:24:23 PM »

As nutty as this might sound I have often wondered if you couldnt design an intake expansion chamber to increase the amount of fuel air charge going into the motor as well, based on the same pulse principles only on the other end. 

~JH
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"Sometimes it is impossible to deal with her, but most of the time she is very sweet, and if you caress her properly she will sing beautifully."
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« Reply #4 on: May 06, 2010, 06:13:59 PM »

As nutty as this might sound I have often wondered if you couldnt design an intake expansion chamber to increase the amount of fuel air charge going into the motor as well, based on the same pulse principles only on the other end. 

~JH

Thinking out loud, you don't have the same kind of velocity that the expanding gasses on the exhaust have on the intake side, nor the strength of the pulses.
 
Maybe Dr. Goggles will chime in on this one - He's become a bit of a student of Walter Kaaden vis a vis Brett de Stoop of late.
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« Reply #5 on: May 06, 2010, 07:33:31 PM »

the shape of a 2stroke expansion chamber is to help scavenge the intake ports..... totally useless on a blown motor that efficiently stuffs the cylinder..... if his blower truly does work, he would be better off with a unrestricted straight pipe
kent
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Seldom Seen Slim
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« Reply #6 on: May 06, 2010, 07:40:26 PM »

So - the pressure wave coming out the exhaust port helps scavenge the cylinder just before the piston closes the port, right?  Is that pressure wave created by the first change in diameter -- the one at the "beginning" of the exp. chamber -- or is there also a pulse created at the other end, where the diameter drops back to small?
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Jon E. Wennerberg
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« Reply #7 on: May 06, 2010, 10:07:38 PM »

Here is some old but good stuff that may help.  Who hasn't heard of Gordon Jennings?

http://www.datafan.com/TunersHandbook/2-strokefiltered.html

http://www.bridgestonemotorcycle.com/documents/do_you_really6.pdf

It should keep you busy for a while, but I would just get this guy to build one for you (using TSR software):

http://kawasakitriplesworldwide.com/tom%20pipes/tomcats%20pipes.htm
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« Reply #8 on: May 06, 2010, 10:42:58 PM »

Back in the "old days" DKW roadraced a blown two-stroke.....with straight ex. pipes....as Kent noted
a "special" ex. not needed......Again back in the "old days" (late 1950's) I roadraced (solo) 250c.c.
Puch that was a two piston single ........again no chambers needed, it was a special racing engine and it was very fast and noise,  Don Vesco raced the bike a couple of times for me, but said it was way to noise to enjoy the race. Only when the Yam. TD-1 came out did the Puch get beat.   
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Beairsto Racing
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« Reply #9 on: May 06, 2010, 11:06:13 PM »

Very cool! cheers
Any details on the superchager? More pictures?
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« Reply #10 on: May 06, 2010, 11:29:10 PM »

So - the pressure wave coming out the exhaust port helps scavenge the cylinder just before the piston closes the port, right?  Is that pressure wave created by the first change in diameter -- the one at the "beginning" of the exp. chamber -- or is there also a pulse created at the other end, where the diameter drops back to small?

As the exhaust pulse enters the expanding taper in the pipe it expands and creates a negative pressure behind it which draws unburnt fuel into the pipe (as well as the burnt fuel) into the chamber.  When the wave hits the reverse taper it is reflected back as a positive wave "ramming" the unburnt fuel back into the cyinder.  A form of free supercharging if you like.  That, of course, is a very simplified explanation.  If you want to know how it really works read Dr. Gordon Blair.  I went to a lecture by him a long time ago.  I lost him after he said "Good evening.  I'm Dr. Gordon Blair."  How it will work with a blower is questionable. 
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« Reply #11 on: May 08, 2010, 11:58:33 PM »

Seldom,
Down load the link to "The Two Stroke Tuners Handbook" by Gordon Jennings. Great reading that is easy to understand and his expansion chamber calculations work. I used them for several dirt bike expansion chambers I built in the 70s. He is also the originator of my favorite one liner: "Dilute my ignorance"! Great book, great guy, he wrote for Cycle magazine, and he passed away a couple of years ago.

Rex
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