Two stroke exhaust question?

RandyS
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RandyS
Edited Date/Time 1/25/2012 12:21pm
What will a two stroke run like without an expansion chamber? I'm building a little street legal 30s style hillclimber out of a 73 DT1(250). The stock pipe is basically a straight pipe anyway but I want to pit a straight pipe on it with a new school silencer on it. I have a few different 450 silencers, I'll probably use one of those. Will there be enough back pressure or will it run like shit. I'm not too worried about power as long as I don't make it worse than stock. This is what I had envisioned building before I saw this but now I'm using it as a blueprint.

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alphado
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alphado 9/16/2010 10:48am
9/16/2010 10:48am
Good job Newmann, now Matthes isn't going to read this thread!
Bret
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Bret 9/16/2010 10:50am
9/16/2010 10:50am
Early two strokes had straight pipes, a simple length of tube attached to the exhaust port. This created a single "negative" wave that helped suck spent exhaust gases out of the cylinder. And since sound waves that start at the end of the pipe travel to the other end at the speed of sound, there was only a small rpm range where the negative wave's return would reach the exhaust port at a useful time: At too low of an rpm, the wave would return too soon, bouncing back out the port. And at too high of an rpm, the piston would have traveled up the cylinder far enough to close the exhaust port, again doing no good. Indeed, the only advantage to this crude pipe system was that it was easy to tune: You simply started with a long pipe and started cutting it off until the motor ran best at the engine speed you wanted.
motogrady
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motogrady 9/16/2010 11:00am
9/16/2010 11:00am Edited Date/Time 9/16/2010 11:03am


a short pipe, small expansion, with a large diameter stinger gives low end.



a longer pipe with a lot of expansion, with a narrow, long stinger gives revs and top end



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newmann
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newmann 9/16/2010 11:10am
9/16/2010 11:10am
alphado wrote:
Good job Newmann, now Matthes isn't going to read this thread!
No shit. And he probably had a lot of great input to contribute. He's an "industry insider", you know. Sorry, guys.Tongue
Crash82
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Crash82 9/16/2010 11:13am
9/16/2010 11:13am
Put a pretty hand made chamber on that bad boy a down pipe, with a stinger! It looks like someone stole the drain pipe from under the sink now.
newmann
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newmann 9/16/2010 11:20am
9/16/2010 11:20am Edited Date/Time 9/16/2010 11:24am
If it was me, I'd put a handmade raw metal cone downpipe with a long stinger and no silencer whatsoever. Loud pipes save lives!!! Edit, looks like me and Crash may be twins. Brother from another mother?
plowboy
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plowboy 9/16/2010 11:20am
9/16/2010 11:20am
indy_maico wrote:
Perfect pipe for you right here http://cgi.ebay.com/ebaymotors/Hooker-Rare-Pipe-Expansion-DT-RT-250-360-Yamaha-_W0QQcmdZViewItemQQhashZitem4152c05494QQitemZ280561210516QQptZMotorcyclesQ5fPartsQ5fAccessories [img]http://i.ebayimg.com/15/!B2moFP!EWk~$(KGrHqUOKj8E)W9VlNPsBMjOR(CZSQ~~_12.JPG[/img]
Perfect pipe for you right here

http://cgi.ebay.com/ebaymotors/Hooker-Rare-Pipe-Expansion-DT-RT-250-360…


I remember that pipe. My buddy had one on his DT175. I burned myself every time I got near it and the heat shield was just a big cheese grater...slice and dice. It did make more power though...up side/down side.
RandyS
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RandyS 9/16/2010 2:39pm
9/16/2010 2:39pm Edited Date/Time 9/16/2010 2:40pm
motogrady wrote:
a short pipe, small expansion, with a large diameter stinger gives low end. a longer pipe with a lot of expansion, with a narrow, long stinger...


a short pipe, small expansion, with a large diameter stinger gives low end.



a longer pipe with a lot of expansion, with a narrow, long stinger gives revs and top end



That's what I was looking for. I couldn't remember which way it was. This thing is going to have drum brakes and skinny tires, it doesn't need to pull hard, just some low end to get it going. If it's fun to ride I'm going to get a 360 to put in after it's registered.

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