Ducati Sporting Club UK > DesmoDue Race Series > DesmoDue - General Questions and Chat > M620 & u/seat exhaust

[Jolley]

Originally Posted by bradders

but as he said many times it was down on power

the space where the pipes go up thru the shock is very limited and if you looked at his, it had one side much larger than the other. Take a lot of dyno work, messing around and cash to sort that right unless someone got lucky

the M620 doesnt have a hoop tho and I know you can fit a 916 shock so just wondered if there was more space, not got the bike home yet so cant just go have a look, but seems those that know think not

Paul, you could definitely do underseat, and it would work. It looks the nuts and saves a lot of work in an off (of which I had too many). My old B bike had 50-51bhp with the single side exhaust and went down to 48-49 with the underseat and rebuild. However, it isn't that straight forward. I have no direct comparison to the two exhausts with exactly the same motor. In addition, bhp isn't the whole story. Torque is the pulling power, and mine definitely pulled (at times) as well as Senna/Sorted/Ghost/Hugh's bikes, who were all amongst the strongest engines. With (only) 65bhp you should be able to get an underseat exhaust made up to expel the gases fast enough.

I don't see how it would be any harder than on my B bike... the front pipe came under the engine and through the swingarm, then connected with a short pipe from the rear cylinder before meeting the silencer. I don't see why that couldn't be done on a 620. The main technical "problem" with this set-up is that to keep a nice balanced motor the theory states that you should have equal length headers that provide the same flow/backpressure to each cylinder. Obviously this is impossible.

[bradders]

Agree Ron, look so much neater and less to damage - and I'm likely to - I think technically there may be even less space, like I say I don't have one to check at the mo, so as Kev said its probably outside of the subframe as Badger

To get the flow equal, from what I have read you need to have either the same length pipes or one larger than the other to compensate. Which I think yours did if I recall as it went past the hoop.

[Spjallen]

A wise man told me that you should think at the pipework as volume not length. A short fat pipe will be equal in volume to a long thin one.

[bradders]

bit like me versus Hugh? PMSL

[bradders]

Originally Posted by Spjallen

A wise man told me that you should think at the pipework as volume not length. A short fat pipe will be equal in volume to a long thin one.

hopefully they'll have yours as a template for mine

[skidlids]

Originally Posted by Jolley

Paul, you could definitely do underseat, and it would work. It looks the nuts and saves a lot of work in an off (of which I had too many)..

In the 7 seasons of DD I've had a few offs as has Kev P and I can't recall either of us having to replace an exhaust, mine has always been side mounted, started with a Micron can off my CBR6 and then fitted the Harris Can and put the Micron back on the CBR6
Kev P had underseat exhausts for the first two seasons but has run side mounted pipes since then.
Dallas has also had a few crashes and the only time I remember him damaging an Exhaust was in his big crash at Pembrey hairpin when the Brake Disc exploded, the exhaust from that crash is still useable unlike a lot of the bike.

I suppose costs need considering, side mounted cans are easy to pick up secondhand and fairly cheap, so easy enough and cheap enough to carry a spare. Undeseat exhausts are usually bespoke systems that cost a few hundred quid to get made and often they are compromised by the space and gaps available for routing them. Add to that they must weigh more as extra pipework is required and that weight is rear biased.

Certainly works in opposition to fitting a lighter fuel tank, as in take a couple of Kilos off the front and add a chunk of that saving to the rear, go figure

[bradders]

only one I can remember destroying a can was that Ali geezer at the Doom, and he took 3 good goes at it till he got it right!!

[bradders]

Originally Posted by skidlids

Certainly works in opposition to fitting a lighter fuel tank, as in take a couple of Kilos off the front and add a chunk of that saving to the rear, go figure

and weight is important...and better to keep weight low to the ground isn't it?! altho I cant have my shortyy can

[Cranker V2]

Sure ley a can thats meets the required 105dB limit is all that is required, whether it be long or short............

[bradders]

Originally Posted by Cranker V2

Sure ley a can thats meets the required 105dB limit is all that is required, whether it be long or short............

think skids is saying it wont. Answer maybe get a 2nd hand one off ebay, fit it, test it and if no good change to a longer one