- Wed Nov 25, 2020 10:32 am
#94189
Presto, I think you will find the exhaust valve opens at 75 degrees BBDC [before bottom dead centre] towards the end of the firing stroke, while the piston is still moving down after firing. Some exhaust valves begin opening around 85 degrees BBDC, or just after mid stoke on the firing stroke.Presto wrote: ↑Wed Nov 25, 2020 9:21 amBoth inlet and exhaust valves are closed on the compression stroke and the power stroke. On a 500 Bullet (for instance) the exhaust valve does not begin to open until 75 degrees BTDC on the EXHAUST stroke [the upward stroke AFTER the power stroke]. The exhaust valve closes 60 degrees ATDC on the INDUCTION stroke.
The exhaust valve is still open as the piston descends on the induction stroke and this is when reversion occurs – as the partial vacuum in the cylinder draws gases through both induction and exhaust ports. This is an inevitable primary tendency – as ‘nature abhors a vacuum’ – to which any ‘shock’ wave, exhaust pipe length or design is secondary.
As the man said –
Reversion is simply the flow of exhaust gasses back into the combustion chamber when the downward movement of the piston creates a vacuum in the cylinder. This event occurs when the camshaft is on the overlap, i.e. the exhaust valve is still open as the intake stroke begins.
And so, M’lud, I rest my case.
