CB360 - Monoshock Brat
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compoundcycles
Been Around the Block
teazer said:
Secondary pipe? The 2 into 1 collector will hook directly up to the headers and make straight pipes 2 into 1, then I'm gonna slap a muffler on the end of that. What tables are you referring to teazer?
Primary tube is the header, Secondary tube is the tailpipe that goes to the muffler. There's a table on one of the mandrel bend companies web sites that shows the size relationship for different tube sizes. I can't remember where I got it from, may have been Megs (cone eng) or may have been SPD, I can't remember which.
I just found it again http://www.coneeng.com/pdf/Area_Calculation_Table.pdf
And remember that in a perfect world the collector outlet will then flare out slightly to a larger size. That creates a venturi effect and it helps the exhaust to work better. Check this out to see more on the subject. http://spdexhaust.com/MC_B.html#
or http://spdexhaust.com/pdfs/2011_Print_Catalog.pdf for a whole lot more information. It all depends on what your objectives are for that exhaust - looks or performance - or every possible last ounce of performance
I just found it again http://www.coneeng.com/pdf/Area_Calculation_Table.pdf
And remember that in a perfect world the collector outlet will then flare out slightly to a larger size. That creates a venturi effect and it helps the exhaust to work better. Check this out to see more on the subject. http://spdexhaust.com/MC_B.html#
or http://spdexhaust.com/pdfs/2011_Print_Catalog.pdf for a whole lot more information. It all depends on what your objectives are for that exhaust - looks or performance - or every possible last ounce of performance
compoundcycles
Been Around the Block
Cool. Thanks for the info teazer I'll definitely read up. Off hand I would say that I plan to mount the universal cone muffler as close to the collector as possible. This would do exactly as you suggest, give the exhaust some expansion room as soon as it leaves the collector.
If you read back through Sonreier's paper, you will see that he correctly refers to primary and secondary headers in a 4-2-1 system which make a broader power band typically than a 4 into 1 system. Since we were talking a simple 2 into 1 design, I loosely referred to the tailpipe as the Secondary. Please keep that in mind.
One interesting thing picked up by AG Bell some years ago is that the idea behind a collector is to reverse a pressure wave and the sharper the change, the stronger the pulse (over a shorter time). Merge collectors dampen that pulse to the point that it's not really generating much of the pulses that all the theory talks about. Instead, teh focus of a merge collector is smooth gas flow management - gas inertia.
A merge collector trades off pulse strength for inertia reduction.
Point of all of that is that it's easy to get hung up on equal length headers at the perfect length for some theoretical peak power revs and in the real world that's not as important as getting rid of gas in an orderly manner. The advantage to using an appropriately sized pipe after the collector is that it opens up more choices for muffler inlet pipe diameter.
There's a great article on the web at the site that that collector picture came from. http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm
One interesting thing picked up by AG Bell some years ago is that the idea behind a collector is to reverse a pressure wave and the sharper the change, the stronger the pulse (over a shorter time). Merge collectors dampen that pulse to the point that it's not really generating much of the pulses that all the theory talks about. Instead, teh focus of a merge collector is smooth gas flow management - gas inertia.
A merge collector trades off pulse strength for inertia reduction.
Point of all of that is that it's easy to get hung up on equal length headers at the perfect length for some theoretical peak power revs and in the real world that's not as important as getting rid of gas in an orderly manner. The advantage to using an appropriately sized pipe after the collector is that it opens up more choices for muffler inlet pipe diameter.
There's a great article on the web at the site that that collector picture came from. http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm
PJ, It's already happened. If someone thinks that their 10,000 rpm (on a good day) bike needs the same pipe dimensions as a 19,000 + MotoGP bike, good luck to them.
I need to start making tapered headers out of inconel for the cafe race scene. ;-) Titanium is so 2012 already.
I need to start making tapered headers out of inconel for the cafe race scene. ;-) Titanium is so 2012 already.
neevo
Over 1,000 Posts
The maths is actually quite hard to work out, especially when you have to convert it all into inches. But I'm sure its worth the effort to know that the changes are going to add some performance as well as look cool.
I did a spreadsheet for 4 cylinders if anyone wants it. Just have to enter some details and it will auto calculate preferred header diameter, length and secondary diameter.
I did a spreadsheet for 4 cylinders if anyone wants it. Just have to enter some details and it will auto calculate preferred header diameter, length and secondary diameter.
compoundcycles
Been Around the Block
All maths aside, here's what I made. I can't say I'm totally in love with it, but I do think its interesting. Also, I made it too long and forgot to leave room for the muffler. Wrapped straight pipes? No, too loud. I think i'll cut about 8 inches out of the whole setup and get the pipes coming more straight back rather than out left too far. Or leave it and wrap it? Thoughts?
Attachments
MJPriceisright
Coast to Coast
how does it feel when your'e on it? seems like its coming out too far away from the bike, but i guess that also depends on rearset position.. i like your idea about cutting it back a bit and running a muffler.
You and the other comments are right, It's a great dry run and now it's time to make the real one. That's usually the way that learning works. It's all good practice.
Leaving aside the math which really apply at one rpm setting, I'd chop the pipes off at roughly at the front of the carbs and then add a short collector made from two curved pipes like the TBR video and have the tailpipe from there back.
Try to find a set of pipes of the right size tube and cut part of the bend out to make the collector from. Feel free to get the secondary from your local muffler shop if they can put a couple of shallow bends into the pipe that you can cut and weld into shape, of cut pie wedges out to curve it to make it hug the frame nice and tight. But leave enough space for the muffler.
Leaving aside the math which really apply at one rpm setting, I'd chop the pipes off at roughly at the front of the carbs and then add a short collector made from two curved pipes like the TBR video and have the tailpipe from there back.
Try to find a set of pipes of the right size tube and cut part of the bend out to make the collector from. Feel free to get the secondary from your local muffler shop if they can put a couple of shallow bends into the pipe that you can cut and weld into shape, of cut pie wedges out to curve it to make it hug the frame nice and tight. But leave enough space for the muffler.
7aliveatlast7
the bearded hessian
took me 3 tries to get mine how i liked it! i kept thinking "i can't cut it up now and start over!" but i knew if i didn't, it'd always be in the back of my head bugging me. so i did it, and don't regret it at all!
compoundcycles
Been Around the Block
Awesome, thanks for the suggestions everyone. I needed to accept the fact that I'm going to do it over. Shorter is better. I'm going to wait for the muffler so I can size it all up together before chopping any more header off. This is the last piece I need to complete before I move on to painting the frame and putting her all together so I'll get it right first.
neevo
Over 1,000 Posts
Part of the fun is having a go, not being happy, throwing it away, learning a bunch, doing it again and eventually nailing it.
Can't count how many times I've looked at a part I've made and not been happy with how it turned out. Every time I've bitten the bullet and redone it, never been disappointed!
Keep it up dude, coming together nicely.
Can't count how many times I've looked at a part I've made and not been happy with how it turned out. Every time I've bitten the bullet and redone it, never been disappointed!
Keep it up dude, coming together nicely.
