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Originally Posted by kircher
Are there cam grinders that take your rod:stroke ratio into account when doing custom grinds? It's my belief that with a higher rod ratio, you wouldn't need as much overlap to get the same effect, due to the longer dwell near TDC.
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They should take the geometry into account. As the rod/stroke ratio decreases, the maximum instantaneous velocity closes in on TDC either side. The piston's velocity coming away from TDC pulls in mixture faster, so the intake cam event especially, should match it.
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Question: When a piston crosses top dead centre and starts to reverse its directon, for an instant its velocity has to equal zero. (Can't change direction without stopping)
So does that mean the entire rotating assembly of an engine stops completely twice per revolution (on a flat-plane crankshaft), or do the connecting rods stretch; letting the crankshaft keep rotating, but for the pistons come to a halt?
It's just something that's got me stumped
Thanks in advance
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Reminds me of the old fixed wheel bike. Would have been interesting if it stopped every time the pedal was at TDC.
Apart from some minor dwell from bearing lash, crank deflection, rod flex, piston side slap, bigend and gudgeon moments, etc the time interval where the piston transitions from relative +ve to -ve velocity is extremely short lived. I can see where you're coming from though; if the crank pin/throw is still moving, but the piston is stationary, something must be taking up the slack of the tensile and compressive forces and rod stretch is a candidate. I'd go with the combination slack of all the clearance fit bits 'n bobs.