CB650SC Exhaust pulses Q?

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daveyg
Posts: 10
Joined: Mon Sep 28, 2009 1:34 pm

CB650SC Exhaust pulses Q?

Postby daveyg » Wed Aug 15, 2018 11:53 pm

So I’ve got a 1985 CB650SC that I am working on getting back on the road, previous owner very roughly chopped the exhaust off at the bottom of the header pipes, just after they turn back under the bike, and I need SOME FORM of muffler(s) to not go completely crazy. My question is sort of regarding the firing order, and as such, the exhaust pulses. I’m not too worried about equal length, but from my googling, it appears we have a 1,3,4,2 firing order, is that correct? So ideally if creating a true dual 4-2 we would want pipes 1&2 joined on the right and 3&4 joined on the left, correct? And a crossover could be used, like what I believe the stock originally had, just to balance the pipes, but not really 100% necessary when creating a custom setup. What would be the result if I were to go from the stock position with 1.25” mandrel bent steel, and joined 1,3 on the right, starting with factory headers, then having 3 cross over and join 1, then having 2,4 join up on the left with pipe 2 crossing over and dipping under pipe 3, keeping 2,3 separate? Would the resulting longer pipes on 2,3 joining the opposite sides, net me a sound somewhat reminiscent of the raspy sound they get from drastically unequal length headers of a old VW or modern Subaru car? Just trying to wind up with something subtly different, don’t want it to sound like a 57 degree twin or anything crazy, just a little different from every other 4 banger out there.
DD:2008 EX650R
Project: 1985 CB650SC

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Volker_P
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Location: southern Germany

Re: CB650SC Exhaust pulses Q?

Postby Volker_P » Thu Aug 16, 2018 3:35 am

daveyg wrote:What would be the result if I were to go from the stock position with 1.25” mandrel bent steel, and joined 1,3 on the right, starting with factory headers, then having 3 cross over and join 1, then having 2,4 join up on the left with pipe 2 crossing over and dipping under pipe 3, keeping 2,3 separate?

Or was it crossing before go up? :lol:

I have no idea of that kind of sound modification possibilities but if you really expect an answer from anybody, I guess one would need at least a drawing here.
Cosky's great (free) online manual: http://cosky0.tripod.com

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daveyg
Posts: 10
Joined: Mon Sep 28, 2009 1:34 pm

Re: CB650SC Exhaust pulses Q?

Postby daveyg » Thu Aug 16, 2018 10:21 am

Attached a crappy scribble of the pipes I’d like to build. Without getting too crazy and busting out some CAD work, this is roughly what I mean to do. So with every 2 revolutions of the crank, you’ll get 2 exhaust pulses close together on each respective muffler, and the head pipes for cylinder 2 and 3 will be approximately 1.5x as long as the head pipes from 1 and 4, kind of like how a Subaru uses, where cyl 1,3 fire and go into the short side of the exhaust, then 4,2 fire and feed into the long side of the exhaust.
Attachments
10139111-9001-4D6B-AC18-1D11408BC9C9.gif
10139111-9001-4D6B-AC18-1D11408BC9C9.gif (22.61 KiB) Viewed 549 times
0EB54CD4-6B90-4F36-9B91-8072D7FA6D76.jpeg
0EB54CD4-6B90-4F36-9B91-8072D7FA6D76.jpeg (1.35 MiB) Viewed 549 times
DD:2008 EX650R
Project: 1985 CB650SC

daveyg
Posts: 10
Joined: Mon Sep 28, 2009 1:34 pm

Re: CB650SC Exhaust pulses Q?

Postby daveyg » Thu Aug 16, 2018 10:57 am

Another oddity I just noticed... most other bikes I’ve looked up (CB750, GSXR) run 1,2,4,3 firing order. Not that it really effects my project, just curious why they’d defy convention and make the CB650 different than the 750... and to relate this back to my project, most 4,2,1 (tri-y aftermarket exhausts geared toward equal length and performance have pipes 1,4 at one collector Y, 2,3 at the other, this makes sense when trying to get the best possible flow at the Y, you’d want opposite firing cylinders (360 degree separate) sharing a collector, I am more interested in getting a unique sound, without being just plain too loud even if it is at the cost of 5-10 hp. If I wanted to get my bike to really duplicate as close as possible the sound of a boxer 4 engine, I’d equally join 1,3 and 2,4 and then make the sizable loop off of the even numbered collector, back to make a third Y joining them all together, kind of like my attached pic with this post.
Attachments
A1C9342F-B18C-40AC-B0F8-C2BDEE71AA5A.jpeg
A1C9342F-B18C-40AC-B0F8-C2BDEE71AA5A.jpeg (1.49 MiB) Viewed 548 times
DD:2008 EX650R
Project: 1985 CB650SC

daveyg
Posts: 10
Joined: Mon Sep 28, 2009 1:34 pm

Re: CB650SC Exhaust pulses Q?

Postby daveyg » Fri Aug 17, 2018 10:40 am

Well, just ordered some 1.5” mandrel U bends. Should be here in 3 business days or less. Wish me luck! Haha
DD:2008 EX650R
Project: 1985 CB650SC


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