Modification to an exhaust...

[jemdna]

Hey everyone

Got a bike here with 2 exhausts on. Each pipe has a "box" with what looks like some kind of breather pipe attached at the other end.

Any suggestions to what this is, and what it does? I want to chop a section of the exhaust off and put turnouts on, but don't want to mess up mixture etc if these things here are some kind of weird emissions type thing.

From what I can tell it doesn't connect to any kind of ecu or anything so not entirely sure what its for?

Cheers everyone

Bry

https://bryanhardy.co.uk/wp-content/uploads/2011/06/zorst.jpg

[Drake]

egr? exhaust gas recirculation? does it go near the airbox?
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was: derbi senda, aprilia sx125, nsr250 mc16, cagiva mito, cb600 hornet now: mk1 bandit, KR1S, landrover series 3 light weight 2.5 petrol, 5speed box

[Drake]

egr? exhaust gas recirculation? does it go near the airbox?
____________________
was: derbi senda, aprilia sx125, nsr250 mc16, cagiva mito, cb600 hornet now: mk1 bandit, KR1S, landrover series 3 light weight 2.5 petrol, 5speed box

[jemdna]

Both pipes come out near the air box but point out away from it, underneath the petrol tank, seemingly go no where (or at least they don't now! It isn't to say a previous owner has moved stuff about and not put them back )

[Drake]

might have been removed for better power
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was: derbi senda, aprilia sx125, nsr250 mc16, cagiva mito, cb600 hornet now: mk1 bandit, KR1S, landrover series 3 light weight 2.5 petrol, 5speed box

[DrDonnyBrago]

Looks like an emissions thing, putting fresh air into the exhaust or similar - I'm guessing a chinese bike because it is rusty but new enough for an emissions based thingymajig so a parts fiche is out fo the question?


Remove it and see what happens .

[jemdna]

telling by the rust hehe!

So yeah its Chinese, hence the rust

Forcing natural air in to the exhaust? Any ideas why? Is it some kind of cheap way of reducing the reportable emissions from the exhaust for EU laws or something?

Diagrams wise I have only managed to find:

https://www.chinesemotorcyclepartsonline.co.uk/enginediagrams_244FMI.php

https://www.chinesemotorcyclepartsonline.co.uk/diagram_13.php

Neither really seem to clarify what that part is for

Bry

[DrDonnyBrago]

EGR - exhaust gas recirculation

Basically - some of the exhaust gases are fed back into the inlet manifold in order to increase the mass of gases in the combustion chamber - the higher mass is harder to heat up and therefore the air/fuel mix doesn't get anywhere near as hot (it doesn't replace fuel or air as it is injected downstream of the carbs/throttle bodies, just adds exhaust gas to it so the fuelling without it should technically be the same).

Because it is harder to heat it doesn't get as hot and cannot reach the silly high temperatures needed to split the oxygen and nitrogen in the air and make nitrogen oxides (NOx) that make up smog.


The other thing it could be is secondary air injection. In this case fresh, clean air is pumped into the exhaust in order to help burn off any excess fuel in the exhaust gases. Nowadays most new bikes have catalytic converters which do this job but air injection is a cheap and pretty good way of doing it, also helps get the cat up to temp quick so you could have both secondary air injection and a cat, or just a secondary air injection device.

If the pipes coming from/to the device are thick and heat resistant then I'd go with EGR, if they are thin and look like they would burn in the presence of hot exhaust gases I'd say secondary air injection. I'd hazard that yours is secondary air injection as it is cheap, common on wee import bikes and gets them through emissions tests. It also has a rubber pipe which would burn easily if it was EGR and the box it is attached to is probably just a one way inlet valve so that hot gases aren't pumped into your airbox fecking everything up.

Either way it is almost certainly an emissions thing and the bike "should" perform fine without it, if it is unplugged anyway then it isn't doing whatever it is supposed to be doing so the pandas, dolphins and penguins are going to die either way . Make sure you havent got any unplugged holes in your airbox now though as it could be pulling dirty air into the engine or making it run a bit lean.

HTH

[Rogerborg]

Yup, I'd go with SAI as well. There's no emissions test in the MOT, so Do What Thou Wilt shall be the whole of the law. If you're mucking around with the exhaust just be sure to keep an eye on the fuelling and rejet as necessary.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[jemdna]

The pipes feel fairly thick, rubber made. Not entirely sure how well they would respond to exhaust gases mind you. The other thing that makes me question it would be the fact that now I have had a proper look about, there doesn't seem to be any where obvious where this would re enter the combustion setup (e.g airbox etc)

So I guess I would go with the second theory that it is drawing in fresh air to act as a cat.

With that in mind, if I decide to cut the pipes, just keep an eye on fuel mixture (plug chops etc) to make sure it hasn't decided to suddenly run lean/rich. Also with these little devices, I figure that if I cut after them anyway, it probably won't make much difference?

Cheers for the help everyone

Bry

[DrDonnyBrago]