under bike exhaust

[bobtrx]

Time to play again , I want to do a exhaust system under the bike like a buell etc. I have standard headers and Over system to work out header lengths but don't have any info on muffler dimensions to suit . is there a distance from collectot to muffler Is there a formula , can anyone help in this area

[phuk72]

I think you'll struggle to get this to work.

Ground clearance will be an issue and having such short headers is bound to mess up performance.

Goof luck though - can't wait to see the results

[Killerwhale]

Time to play again , I want to do a exhaust system under the bike like a buell etc. I have standard headers and Over system to work out header lengths but don't have any info on muffler dimensions to suit . is there a distance from collectot to muffler Is there a formula , can anyone help in this area

Kinda like "froggies" bike!?

[phuk72]

But he didn't have the stock swing arm or shock linkage to worry about

[Killerwhale]

But he didn't have the stock swing arm or shock linkage to worry about

K I N D A like the frog´s bike....

[phuk72]

K I N D A like the frog´s bike....

[davesta]

Perhaps you could source an exhaust off a bike that already has an undertail exhaust and modify it? The er6 exhaust could be good, becuase it's already a parallel twin. Hmm. But i get the feeling you wanna fabricate it all yourself? Good luck mate, can't wait to see it!

[Dodders]

Hi All
The under bike exhaust seems like a good idea but i don't know weather it will work . I myself like to dabble in the unknown but I try to do a lot of research first . If you look up Google and type in exhaust pulse it will give links and all the information you will need . Some sites even give you some formulas to work with. If you keep looking through some of these sites and even the links it opens your eyes as to why after market exhaust are sooooooo bloody expensive .

Cheers and good luck !

[madivi]

Hi Bob

Not so bad idea I think.
I've been opting a long time for an underseat system but while there are quite nice samples here, I've always found the routing of the downpipes a bit cumbersome.

So I've started the underbike variant - still a lot of work to do.
Ground clearance is definitely a problem and I'm still not sure whether I'll accomplish it properly.
Some hints as what to look at:
- Drop the forks all the way till level with top yoke
- Lift the rear by longer dog bones accordingly
This gives you 2 to 2.5 cm.
- Get yourself some oval mufflers (I got an underseat pair from a BMW R 1100 s)
an ER-6 is a good starting point but hard to get here.
- Place mufflers behind the oil sump (saves height)
- Displace the sidestand farther out (allows for the mufflers to protude on the left hand side)
- Allow the mufflers to spread past the rear shock (you get a V-alignment)
Doing so I manage to get more than a full hand clearance - which is not much.

Then there is a performance issue. One approach might be, to join the headers at the mufflers rear end and to route the front end back to the tail. Depending on the mufflers dimensions and number this might be viable, in my case it's not (two mufflers).
I'll simply try to connect the ultra short headers to the mufflers. I expect this to spoil power at high revs whereas getting maybe better response at low ones. As you I have little knowledge. Somewhere here I read that header volume doesn't compensate for length.
So this all is going to be a genuine blind experiment. Maybe I'll play around with flexible tubing before running into all the welding.

More is to come... If you need some visual hint I may take some pictures

[Wombat]

Bob,

Can't remember where this came from but it might be of some assistance
http://www.mez.co.uk/mezporting/exhaust_length.html

Bob

[phuk72]

Hi Bob

Not so bad idea I think.
I've been opting a long time for an underseat system but while there are quite nice samples here, I've always found the routing of the downpipes a bit cumbersome.

So I've started the underbike variant - still a lot of work to do.
Ground clearance is definitely a problem and I'm still not sure whether I'll accomplish it properly.
Some hints as what to look at:
- Drop the forks all the way till level with top yoke
- Lift the rear by longer dog bones accordingly
This gives you 2 to 2.5 cm.
- Get yourself some oval mufflers (I got an underseat pair from a BMW R 1100 s)
an ER-6 is a good starting point but hard to get here.
- Place mufflers behind the oil sump (saves height)
- Displace the sidestand farther out (allows for the mufflers to protude on the left hand side)
- Allow the mufflers to spread past the rear shock (you get a V-alignment)
Doing so I manage to get more than a full hand clearance - which is not much.

Then there is a performance issue. One approach might be, to join the headers at the mufflers rear end and to route the front end back to the tail. Depending on the mufflers dimensions and number this might be viable, in my case it's not (two mufflers).
I'll simply try to connect the ultra short headers to the mufflers. I expect this to spoil power at high revs whereas getting maybe better response at low ones. As you I have little knowledge. Somewhere here I read that header volume doesn't compensate for length.
So this all is going to be a genuine blind experiment. Maybe I'll play around with flexible tubing before running into all the welding.

More is to come... If you need some visual hint I may take some pictures

So, to summarise.

You're going to bugger up the handling, reduce ground clearance and and (very probably) affect the performance.

Now I'm all for "because I can" but this mod really does seem to be form over function.

Still, can't wait to see the results

[madivi]

Well you're right, it's about looks.
The handling though shouldn't change (except for center of gravity).
I'll keep you posted.

[phuk72]

The handling though shouldn't change (except for center of gravity).

Yes it will - jacking up the rear end will compress the shock and also change the angle of the swing arm at the pivot

[bobtrx]

Thanks dodder , wombat for the info . Bike suspension settings will not be changed , madivi I wouldn't even think of changing the fork height ,it would make the bike steer like a boat . I will keep the header length and hopfully pipe size the same as the OVER headers on it now . I need to move the headers to come under the motor on the right hand side with maybe the collector on a 45 degree angle to give a little more room for the muffler . After the collector do a 180 degree smooth bend with 50 - 60 mm pipe into a 50mm inner baffle size and enclose it in a oval muffler that exits down to the left side somewhere near the front of the motor . I'm looking for some one who can bend pipe as I want it . Last set of headers I had made by an exhaust shop I could have done a better job with a hammer and block of wood . I also have the standard headers to use if needed , cut and make to tuned header length . I'm still in the think tank with this project and I THINK I need a stubbie , anyone want one while I'm at the fridge

[madivi]

...I wouldn't even think of changing the fork height ,it would make the bike steer like a boat...

Would it, if you lift the rear end by the same amount (thus keeping steering angle)?
Of course due to longer fork legs, you get a longer caster but I wouldn't expect
this to be of relevance. Thoug I haven't calculated it yet...