Yes, that sums it up nicely to the point we've gotten so far.

Instead of "effective compression," I like the term "working pressure," which relates to the amount of intake charge. At small throttle, there's not much charge and even a very high CR motor can't develop enough pressure to destabilize the fuel and ping. Conversely, even a low CR motor can develop excessive pressure if it can flow enough intake charge.

The burn rate is roughly proportional to the working pressure, which is why I like vacuum advance dizzies hooked to the full manifold vacuum. At small throttle / low pressure / slow burn / high vacuum, this provides lots of advance so the max burn happens when the piston is in position to receive the energy transfer, which makes for excellent economy. At wide throttle / high pressure / quick burn / low vacuum, it retards and doesn't light off the mix too early, which is what causes pinging.

I know exactly what you mean -- the R cam in a stock motor comes on like throwing a switch. Here's where we can play with tuning the length of the intake, thereby altering the mass / inertia of the charge, and with tuning a header and exhaust to get that mass moving quickly very early in the overlap part of the cycle, essentially bypassing the disruption. This is also where modern cam profiles have it all over the archaic Volvo and Isky grinds.

As John Parker has pointed out several times recently, a motor with a modern cam, and intake and exhaust characteristics that match it (or vice versa), we can now get terrific power increases with NO loss of tractablility -- no trade-off between low end torque and high end horsepower, just lots more of it across the band.

My Unitek-engineered motor is built with exactly that sort of thinking, although the details are entirely different from John's Street Performance kit. On paper, it doesn't sound like it would be streetable at all, yet it idles perfectly at 950 RPM, pulls increasingly harder from 2000 to 7000 without any trace of "coming up on the cam," and gets 30+ mpg on the highway on 92 unleaded with no pinging. First few times I really put my foot in it, I thought the seat backs were gonna snap off.

Anyway, the point that relates to this thread is that there is absolutely nothing wrong with experimenting with lash and thereby cam duration, as Jack seems to have found out. Maybe those factory settings are fine with a restrictive, stock exhaust... but start changing anything, and all bets are off.