[Ducati] exhaust energy, turbos and diesels

[MS&F]

Just a little extra - as the revs increase, the valve openings happen so 
quickly that they start to produce their own harmonics.  We can hear 
down to about 20Hz, which equates to 600rpm on a twin (a 4 only wakes up 
at 40Hz), so a GP bike at 18 000rpm should have exhaust valves opening 
at 1.2kHz - hence the scream.  I guess if we could get them to rev past  
300 000rpm, we wouldn't be able to hear them anymore.

Ronald Betts wrote:
> primary noise is from initial exaust valve opening
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