Father Son 75 CB200T Rise From the Ruins
- Thread starter Texasstar
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Texasstar
Can't is a four letter dirty word
with the added back pressure of the baffles caused the throttle hesitation and was running rich and then we blew off one of the cones so we figured lucky didn't want to be baffled and we wanted to see how Cone constructed the megaphones so we pulled out the saws all. We are about to pull the fairing and go to the dyno to see if we can improve on the 17.3 hp with the megaphones and we need to weld some hoops and make different size lengths of pipe.1sttimer said:
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In all seriousness, though... that previous pic is the formulas for designing a two stroke exhaust pipe.
Four strokes work a bit differently (obviously), but some of the same concepts (and math) apply.
That said, wave tuning the exhaust has fallen out of favor, which is why you don't see reverse megaphone mufflers on modern bikes too often, anymore.
It turns out that four stroke engines respond better to flow than to wave tuning. Your goal should be an open pipe with relatively few bends and enough length such that one exhaust pulse is always in the pipe before the next one has a chance to enter. Some math will be needed to calculate the length... I think I covered it in my "Doing it Right" thread, but I can repost of needed.
Four strokes work a bit differently (obviously), but some of the same concepts (and math) apply.
That said, wave tuning the exhaust has fallen out of favor, which is why you don't see reverse megaphone mufflers on modern bikes too often, anymore.
It turns out that four stroke engines respond better to flow than to wave tuning. Your goal should be an open pipe with relatively few bends and enough length such that one exhaust pulse is always in the pipe before the next one has a chance to enter. Some math will be needed to calculate the length... I think I covered it in my "Doing it Right" thread, but I can repost of needed.
Texasstar
Can't is a four letter dirty word
I have the math somewhere in this string and we heard the megaphones at motogp...http://touch.cycleworld.com/all/110845#1Sonreir said:
I was just wondering about the length of the megaphone and the reverse cone...some megaphones are 12, 18, etc. long and how that impacts the pulse. As we found out at a lower idle it was quieter than an open pipe but we haven't listened to it at 11k...yet.
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In theory, the sharper angles created by a shorter cone result in stronger wave reflections, but over a smaller RPM range.
In practice, it doesn't matter as much on a four stroke as it does on a two stroke. Reverse cone mufflers are largely a aural and aesthetic decision.
In practice, it doesn't matter as much on a four stroke as it does on a two stroke. Reverse cone mufflers are largely a aural and aesthetic decision.
Matt is correct that short fat megaphones make a stronger pulse over a narrow range and longer megs stretch it out. Honda typically work best with long megaphones and very short reverse cone.
Short pipes peak at high revs and long pipes at lower revs, but in general, long megs are best to stretch the powerband.
Matt's also correct that the modern idea with merge collectors is to maximize flow and the tuned length is less of an issue. Stepped pipes work a similar way to send a negative pulse back to arrive at TDC on overlap at high revs.
What's at the front end of those baffle tubes? If they are open at both ends, they should work like a parallel pipe. If one end is closed, they are not going to work so well in your application.
Can't wait to see the next set of dyno charts.
Short pipes peak at high revs and long pipes at lower revs, but in general, long megs are best to stretch the powerband.
Matt's also correct that the modern idea with merge collectors is to maximize flow and the tuned length is less of an issue. Stepped pipes work a similar way to send a negative pulse back to arrive at TDC on overlap at high revs.
What's at the front end of those baffle tubes? If they are open at both ends, they should work like a parallel pipe. If one end is closed, they are not going to work so well in your application.
Can't wait to see the next set of dyno charts.
simo
Been Around the Block
Could you raise Lucky's compression by using a cb175 head? The stock ratio for both the 175 and 200 is 9:1 .in the 200 that's 99cc per cylinder into 11cc at TDC since the 175 is 87cc into 9.6666ccc at 9:1 by swapping heads you get 97.6666cc into 9.6666 so a compression ratio of 10:1 on paper anyway
Or am I missing something
Or am I missing something
thanks Simo that's an interesting option. 11:1 
