2 stroke exhaust theory.

RandyS
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10/25/2016 4:39pm
I think I might have asked this before but I can't find the thread. I've got a 73 dt250 that I was going to make a vintage MXer out of so I sold off a lot of the parts down to the frame. I decided to make kind of a bobber out of it similar to the one in the picture. I don't have a pipe so I was thinking about taking a few of the stainless 4 stroke stockers I have and having a friend tig up a pipe that would be tucked in and not in the way. I know trials bikes don't have much of an expansion chamber and they're all low end although the FMF Fatty kind of goes against that thought so I'm a little confused. The stock Yamaha pipe didn't have much of an expansion chamber and what it had was at the end so it never really made back pressure like a modern pipe. What would a straight pipe with a silencer run like? It would still have a larger chamber, maybe half the size of the bike below. Also a welder question, would media blasting the area to be welded be OK or is the used stainless going to be a nightmare?
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WRH
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10/25/2016 4:55pm
Okay, somebody from two stroke tech could run a SIM for you with bore,stroke,port timing,etc.but basically just take the pipe off and run it and you would get an idea. Except it would have bottom end. Basically anything worth doing is worth doing right. You could at least..... run the simplest design of the first chambers built. To give your engine a chance at making any power. I would call power pros or bills and get one custom built.Actually I would take it to John and Dan at jemco. Because they are closer to me. But your out west.
mx317
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10/25/2016 5:02pm
Circle F in Texas might have something also
WRH
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10/25/2016 5:07pm
mx317 wrote:
Circle F in Texas might have something also
Yep them too.
RandyS
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10/25/2016 5:09pm
Forgot to mention that this is going to be low budget. Having a pipe built would cost as much as I'm planning on spending on the whole thing. I've got a couple of 125 and 250 stock Yamaha pipes that I can rig if I have to, I just wanted to do something that wasn't in the way. Power isn't a huge issue as long as it puts out as much as stock. Looking at that pipe I don't see how I could do any worse.

The Shop

WRH
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10/25/2016 5:15pm
If you want to know how it will run before you put a lot of work into it. Find a way to attach it going out in any direction and see if the power it makes is satisfactory. If it is then put the work into making it fit.
motogrady
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10/25/2016 5:40pm

It's just gonna have low end, prob won't rev too good, but hey, wtf, you ain't takin it to the salt flats.

I had a 1970 250 Husquvarna back in the day. Very little bulge, stinger the size of a silver dollar, was a stump puller.

It's s bobber, different is good.
early
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10/25/2016 6:10pm


Yamaha rds had basically straight pipes. Their power was pretty flat i think.

10/25/2016 6:15pm
Could be a top end style pipe. Looks similar to a drag pipe for a Banshee


zehn
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10/25/2016 6:25pm
early wrote:
[img]https://p.vitalmx.com/photos/forums/2016/10/25/157416/s1200_1973_rd350.jpg[/img] Yamaha rds had basically straight pipes. Their power was pretty flat i think.


Yamaha rds had basically straight pipes. Their power was pretty flat i think.

Stockers did yes, but we race a couple RDs and those damn pipes are the first thing to go. They're terrible
Idaho747
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10/25/2016 6:34pm
Don't know much about the type of exhaust to use but media blasting the stainless pipe would help an absolute ton. As long as it's cleaned up after wards. That's probably honestly one of the best ways to prep it
Skidaddle
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10/25/2016 7:08pm
Never go full retard on 2 stroke pipes.

Can never go wrong with cones.

zehn
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10/25/2016 7:10pm
Skidaddle wrote:
Never go full retard on 2 stroke pipes. Can never go wrong with cones. [img]https://blog.stihl.com/wp-content/uploads/2014/10/hot_saw_I-TST-E017.jpg[/img]
Never go full retard on 2 stroke pipes.

Can never go wrong with cones.

JFC is that a 125 chainsaw?
Skidaddle
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10/25/2016 7:12pm
Skidaddle wrote:
Never go full retard on 2 stroke pipes. Can never go wrong with cones. [img]https://blog.stihl.com/wp-content/uploads/2014/10/hot_saw_I-TST-E017.jpg[/img]
Never go full retard on 2 stroke pipes.

Can never go wrong with cones.

zehn wrote:
JFC is that a 125 chainsaw?
They have 250 and 500 classes too.


zehn
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10/25/2016 7:16pm
^^ That sounds like a great way to lose a leg Blink
Skidaddle
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10/25/2016 7:17pm
There is not much sexier than a sick ass 2 stroke pipe.
I dont care what its on.

Skidaddle
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10/25/2016 7:23pm
When ya need a 2 stroke fix, just tell the lady need to cut some wood. You know, to snuggle by the fire.

Skidaddle
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10/25/2016 7:27pm
early wrote:
[img]https://p.vitalmx.com/photos/forums/2016/10/25/157416/s1200_1973_rd350.jpg[/img] Yamaha rds had basically straight pipes. Their power was pretty flat i think.


Yamaha rds had basically straight pipes. Their power was pretty flat i think.

RandyS
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10/25/2016 10:54pm
motogrady wrote:
It's just gonna have low end, prob won't rev too good, but hey, wtf, you ain't takin it to the salt flats. I had a 1970...

It's just gonna have low end, prob won't rev too good, but hey, wtf, you ain't takin it to the salt flats.

I had a 1970 250 Husquvarna back in the day. Very little bulge, stinger the size of a silver dollar, was a stump puller.

It's s bobber, different is good.
Thanks, that was my thinking. I don't need to ring the thing out. As long as it pulls off the bottom I can gear it tall, it's going to be street legal as long as DMV doesn't shut me down. I want it to be loud to piss the hippies around here off but not too loud. I have a bastardized Husky pipe that came on my 73 250WR, not sure what it was pieced together from. Maybe I'll see what I can do with that.
Bearuno
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10/26/2016 2:32am
Even with the RD350 pipes shown above, you'll find divergent and convergent cones to the std pipe . The std pipes were styled as per accepted road bike looks for that time. And, for a 350 2t, they had little need to be particularly highly tuned as a road bike - that little rice burner, in the right hands, just as stock, could put it to most far bigger bikes of the times. And that was with it having a level of tune that gave just over half the HP of the 1973 TZ350A of the time - I think 37HP to the TZAs 60HP .....

The factories had taken Walter Kaaden's 2t tech and had run with it, for well over a decade by then. An expansion chamber doesn't have to look like one of the glorious examples pictured above, to be, nonetheless, an Expansion chamber. Even the flattened bulge DT pipes you describe were still a form of expansion chamber, just as 2t Trials bikes pipes are. A 'box', is still an Expansion / Helmholtz chamber. They are just made for different effects / levels of performance.

Hell you could probably put just about any type of chamber, suitably cut to fit the bike, and it would work better than a straight through, or divergent coned only pipe on a 2t. My Californian boss in the 70s, who started Australia's then version of DG / FMF / PC, = Competition Development, called those things 'bluey pipes', and regarded them with absolute disdain. Go to a wreckers, and find a few pipes to play with, if you won't have a proper pipe made. Oh, and by the way, said 'bluey pipes' are the most disgusting sounding exhausts in the universe, well, other than straight through HD pipes............ ride something like that, and you'll be a deserved object of ridicule, and, probably be quickly locked up, to boot.
a22
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10/26/2016 6:48am Edited Date/Time 10/26/2016 6:49am
Those bike engined chainsaws... wouldn't get me near one, can just imagine burning my arm on the pipe, reacting to getting burnt by moving my arm quickly away.... right into the path of the chain.... no way!!
Got told horrible story once bout a Tree Surgeon who had accident, ever since been very very dubious of chainsaws!

Sweet little bike BTW.
10/26/2016 6:50am
There are pipe design programs that can be found for free on the web. The calculation is pretty basic. For cheap fabrication, check out hydroforming videos on YouTube. Basically all you need is a pressure washer and a welder. You would save a lot of money compared to having it done custom, but expect to spend a lot of time doing it.
Berm
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10/26/2016 8:15am
Skidaddle wrote:
There is not much sexier than a sick ass 2 stroke pipe. I dont care what its on. [img]http://i174.photobucket.com/albums/w84/stripper_album/GTG%202015/_MG_0920.jpg[/img]
There is not much sexier than a sick ass 2 stroke pipe.
I dont care what its on.

Even if its on an atv?

p0wn
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10/26/2016 8:43am
DT250 is a pig anyways. Who cares. Just run it with headers.
Skidaddle
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10/26/2016 10:25am
Skidaddle wrote:
There is not much sexier than a sick ass 2 stroke pipe. I dont care what its on. [img]http://i174.photobucket.com/albums/w84/stripper_album/GTG%202015/_MG_0920.jpg[/img]
There is not much sexier than a sick ass 2 stroke pipe.
I dont care what its on.

Berm wrote:
Even if its on an atv? [URL=http://s76.photobucket.com/user/Ryder25/media/photo11_zps917720aa.jpg.html][IMG]http://i76.photobucket.com/albums/j22/Ryder25/photo11_zps917720aa.jpg[/IMG][/URL]
Even if its on an atv?

Still a sick pipe.

Hey, I met my old lady when she had a Methanol burning extended swingarm 10 paddle Taller Hauler overbored Banshee on nitrous.

It had Chrome stinger pipes. No silencers. It sounded sooooo good.

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