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On thinking about it I think you鈥檙e quite right馃榿
 

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Here鈥檚 some useless, self aggrandizing information about why retarded cam timing helps a bit at higher RPM

The fuel/air mixture careening into the engine via the intake port has mass. And it鈥檚 moving, so it has velocity. Momentum equals mass times velocity (P=mv). As revs increase, the charge velocity and therefore its momentum increase. As the piston nears BDC on the intake stroke (at any rpm), a significant amount of cylinder filling occurs because of the momentum of the intake charge. In fact, at higher rpms, this inrush of mixture can actually continue even after the piston has started back up the bore on the compression stroke! But that can only happen if the intake valve is still open and 鈥渞etarded鈥 cam timing is what keeps it open later. Conversely, that same retarded intake cam timing can have the intake valves closing too late in a lower rpm setting, possibly causing the rising piston to start shoving slow moving charge back out the intake tract causing a flat spot, 鈥渞eversion鈥, or even 鈥渄ouble carburation鈥. For more fun, consider that our intake valves open before the exhaust valves are closed (overlap), and lots of rpm-dependent pressure pulses are bouncing up and down the headers. If a specific rpm sees a negative pressure (suction) pulse come back up the header to the exhaust valve during overlap, and we鈥檙e at a higher rpm with high charge velocity, the negative pulse will pull down the cylinder pressure and further aid the intake charge in 鈥渟uper charging鈥 the cylinder. Chasing this powerful effect around the rpm range is what BMW is doing with 鈥淪hift Cam鈥 tech on the S1000RR and 1250 Boxer motors.
 

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Don't forget that if you get your annual service at the dealers you will also sometimes get an ECU update.
That can change all sorts of things.
 
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