Why's it called an "under seat" exhaust when there's one by the swing arm too?

Question

Hey Wiggy et al,

The picture you posted from Nicky Haydon:

http://images.motogp.com/multimedia2/615/615957_15797.jpg

is confusing me (having a blonde moment I think!)

Yes, there is a pipe under the seat, but also another by the back wheel - what's going on there then?

My mates MV has under seat pipes and they are (obviously)under the seat, but this picture (or your description) is puzzling me - why the other placement?

neilgtti · Accepted Answer

Hi Dingo

Most 4 cylinder road bikes have a 4 into 1 (ie 4 pipes into 1 silencer system), a notable exception being the latest generation GSX R 1000. That has a 4 into 2.

Honda obviously think that the optimum performance for their Moto GP bike will be with individual pipes and expansion chambers.  (Cant really call them silencers)

There isn't enough room to fit all the plumbing required under the seat, so some of it comes up the side too.

In oder to get maximum power and/or torque, sometimes the pipework has to be quite long. so it will snake around a bit underneath fairings and stuff. On a road bike where power isn't such an issue, length is not as important and 4 pipes (as in the case of the MV) will fit under the seat.

Hope that helps.

Anonymous · Answer

Well said, Mr Neil, I could not have worded it better myself!

There's a quick ten point for you Sir!

Dingo Honey, your " blonde moments " are your best!

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Why's it called an "under seat" exhaust when there's one by the swing arm too?

2 Answers