Questions for those designing exhaust systems

whitw wings · #1 (**permalink**) 11-02-2009, 02:11 AM

Has anyone ever run a system using a rear system tube that does not go down first? Why not go straight back and up to ta left exist high mount position?

I haven't seen my bike complete for a year now so I don't know if this would even be possible. After looking at some WSBK pics from Simone's recent scans I realized this may be possible. Is there performance gains that would be lost from a "straight shot" off the rear cylinder?

wibbly · #2 (**permalink**) 11-02-2009, 02:46 AM

the point of the rear cylinder pipe going down and linking is to allow for pulse tuning... as the pulse from the front cylinder passes the point where the rear exhaust tube joins it sucks the pulse from the rear cylinder out... it aids in exhaust scavenging... it's the same idea as x pipes you see in cars.

johnyisthedevil · #3 (**permalink**) 11-02-2009, 02:54 AM

you would lose the effects of scavenging. which does improve hp and torque. think of the pipes as dueling syphon guns. one helps the other draw spent gasses out and fresh mixture in. it also helps to balance out flow between cylinders since packaging constraints often dictate two completely different pipes. It would be a cool setup though and would probably have a nice top end hit, but it would sacrifice linearity somewhat.

johnyisthedevil · #4 (**permalink**) 11-02-2009, 02:55 AM

see what happens when you get up to leave a piss. wibbly comes in and beats you to it.

whitw wings · #5 (**permalink**) 11-02-2009, 03:17 AM

Thanks guys for your serious input. DOn't get me wrong, I will not be the one trying to do this but it just seemed logical to do this in light of weight savings. I have seen some interesting Ducati exhaust layouts that essentially do what I was propsing.

wibbly · #6 (**permalink**) 11-02-2009, 03:19 AM

as far as weight savings goes it's best to take it from the top of the bike.. not from the bottom. i'd leave the exhaust and focus more on something like an aluminum tank, battery relocation, monocoque tail etc...

whitw wings · #7 (**permalink**) 11-02-2009, 03:28 AM

WAY ahead of you there wiblly, on my own bike that is!

Now I am just trying to balance my free time with the rc getting a decent split with the NC this winter.

whitw wings · #8 (**permalink**) 11-02-2009, 03:32 AM

What if you met the two pipes together before splitting them of to either side after the front cylinder comes up through the swingarm where the rear cylinder normally would have?

Does that make sense?

johnyisthedevil · #9 (**permalink**) 11-02-2009, 03:37 AM

so you wanna put the merge in the tail section? it would help, but wouldn't be ideal

johnyisthedevil · #10 (**permalink**) 11-02-2009, 03:42 AM

the front and rear head pipes should(in theory) be equal length and join at a place that inhibits reversion of exhaust pulses back into the cylinder. I would think the front head pipe would end up way to long, and the rear you would have to do some serious snaking to get enough pipe in there. kinda like the one version of the rc211v setup where the two rear cylinders joined in the tail, but there was a full 360* donut in there. I'll see if I can find a pic.

wibbly · #11 (**permalink**) 11-02-2009, 03:48 AM

Quote:

Originally Posted by johnyisthedevil

the front and rear head pipes should(in theory) be equal length and join at a place that inhibits reversion of exhaust pulses back into the cylinder. I would think the front head pipe would end up way to long, and the rear you would have to do some serious snaking to get enough pipe in there. kinda like the one version of the rc211v setup where the two rear cylinders joined in the tail, but there was a full 360* donut in there. I'll see if I can find a pic.

i always wondered about this... should the pipes be of equal length with a v-twin firing pattern? i can understand on an i4 but with a v-twin you wouldn't expect identical length pipes to create the same pulse tune... no?

maybe i'm just picturing it wrong...

johnyisthedevil · #12 (**permalink**) 11-02-2009, 03:49 AM

http://www.motorcycle-usa.com/photog...R_RC211V_C.jpg

check this out.

whitw wings · #13 (**permalink**) 11-02-2009, 03:51 AM

whitw wings · #14 (**permalink**) 11-02-2009, 03:54 AM

Ah what do those idiots at HRC know!

johnyisthedevil · #15 (**permalink**) 11-02-2009, 04:07 AM

Quote:

Originally Posted by wibbly

i always wondered about this... should the pipes be of equal length with a v-twin firing pattern? i can understand on an i4 but with a v-twin you wouldn't expect identical length pipes to create the same pulse tune... no?

maybe i'm just picturing it wrong...

true some extent as I understand it. a twin will inherently not scavenge as well or as evenly as a four, but I belive that is why your premium kits like Sato and Akrapovic use different sized pipe on one side. in order to increase the velocity a tad and make the rear cylinder "suck" for a slightly longer period of time. I digress though my twin tuning is pretty limited.

PBMW · #16 (**permalink**) 11-02-2009, 02:31 PM

Read A Grahm Bell's "Performance Tuning in Theory and Practice"
There is a wealth of information about exhaust theory.

**mrgrn** · #17 (**permalink**) 11-03-2009, 03:03 AM

the rear tube is too short and you will lose serious power and that is part of the reason for the dup in the 2-1's, they all have too short a rear header tube by several inches

Defender · #18 (**permalink**) 11-03-2009, 03:41 PM

Amazing balance on the CBR...