Having read this Post & responses, out of curiosity I looked @ Scootopia’s website & the images of their 42 mm Clubman would seem to indicate a reasonably well thought out product. The two part manifold & long cone are preferable & I’m guessing that the tailpipe may be marginally larger than some competitors, which - IMO - is a good thing as it so often contributes to preventing an engine from overheating. The fact that this engine runs a 28 mm carburettor means that there is more to ‘exhaust’ so this particular Clubman would appear to be non restrictive.
As other contributors have said, a ‘Real World’ 69 MPH is pretty good with current fuels & you’d probably only gain more with an expansion chamber.
Over the decades, I have gained some experience of exhausts from OEM to gutted - ‘straight through’ - OEM, Clubman’s up to 50 mm Ancillotti’s & various expansion chambers. What I believe to be critical are the bleedpipe dimensions. Not only does the tailpipe contribute to the cylinder temperature, it can so easily be overlooked by ‘backing up’ @ WOT or on the over-run as I recall on Cadwell’s ‘Club’ circuit where my bike would absolutely fly out of the hairpin, only to be passed in the dip of the next long straight. This dilemma was purely due to the tailpipe size - plus my ignorance
To sum up, I’d be interested to know the tailpipe bore of the exhaust & - although it may benefit even more from being enlarged - I would suggest that it’s longevity & performance may be improved further by re-engineering the mounting to the engine.
Vibration is what causes an exhaust to split & fail. The last DIY Clubman type exhaust I constructed incorporated bobbin type AV mounts in conjunction with sprung connection of the cone to the ‘U’ pipe. This was achieved by the main, top (to crankcase side) bracket & bending the cut edges in opposite directions & mounting two bobbins between. The bottom (to crankcase bottom) bracket was simply bent down to a right angle & a bobbin fitted between that & another DIY right angle bracket to fit in place utilising the single M8 fixing point. As the ‘box had been gutted & sliced to allow greater ground clearance, a silencer was essential & this too was mounted with AV mounts.
To this day, my view is that Innocenti got an awful lot of things ‘right’ by comparison with the competition & shed load of components spawned by many hoping to capitalise on the gullibility of many of us. For very good reason, they used simple crankcase breathers fitted with wire mesh filters, crankcase mounted gear change components made of steel, rather than colourful soft alloy etc etc. Yet, despite having the knowledge in allowing for vibration as demonstrated by the laminated horn mounts, that same philosophy was not extended to the exhaust
Posted: Wed Jan 01, 2025 10:40 pm