acotrel wrote: I cannot understand how it increases bottom end, if it is a standing wave effect.
acotrel wrote: I was told by one competent tuner that the modern bikes are faster when the Exup valve has been ditched.
Rohan wrote:Exup was all the rage in MotoGP at some point - at least the Ducs had it.
Was this for noise ??, or more torque low down in the rpm register.
Some of the other marques too ?
Sometimes with electrically variable inlet trumpet lengths, so they were chasing something.
Quite a number of strokers (bluesmokes) had it too, with expansion chambers,
so noise can't been solely the purpose for them either . ??
acotrel wrote:This matter is also relevant to road motorcycles. When you set up your cam timing, do you OPTIMISE it by moving the timing backwards and forwards to see where it operates best for your purposes ? I am always suspicious of motorcycle manufacturers. Would anyone really claim that Pa Norton did not move the cam timing in the Commando back a bit from best, to comply with the noise laws ? If Exup achieves noise reduction rather than anything else, it might help the situation where you want performance from your road bike without getting booked for noise pollution. i.e. move the cam forwards and fit Exup ? Fitting a throttle-operated butterfly valve into the pipe after the collector on a 2 into 1 exhaust would be a soda.
acotrel wrote:I have always found it difficult to imagine how flow happens when there is a standing wave. I understand it happens by mass transfer, however in my reasoning each pulse must move down one every time there is a firing in a single cylinder motor and pop out the end of the pipe. However if you think about how a tsunami works, it is all about energy.
acotrel wrote: I doubt that midrange power can be measured with enough sensitivity to give meaningful results.
acotrel wrote:The horsepower figure which comes off inertia dynamometers is usually adjusted with a fiddle-factor which relates it to the specified figure for the Yamaha Vmax - the bench-mark.
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