livvie — What I was getting at is the following. If we take a conceptually ideal Otto-cycle engine, with intake and exhaust valves each open for precisely 180 degrees of crankshaft rotation, the compression and expansion ratios are equal, and set by the stroke length and chamber dimensions. If we now retard the closing of the intake valve so that it only closes partway up the compression stroke, then some of the fuel/air mixture that has already been sucked into the cylinder is blown back out into the intake manifold before the valve closes, and so after the intake valve closes the actual compression ratio achieved is much lower than the above "theoretical" ratio. This is what the so-called "Atkinson"-cycle hybrid engines do. The Camry's hybrid ICE delays its intake valve closing by more than 30 degrees compared to that of the non-hybrid ICE. This makes its effective compression ratio still around the 9.8:1 value specified for the non-hybrid engine, and thus suitable for regular gasoline. However, because of this strategy, its effective expansion ratio is now larger than its effective compression ratio, and this is what leads to its greater thermodynamic efficiency. In reality, both intake and exhaust valve openings and closings do not occur at the precise top or bottom of the piston's stroke, and this complicates computing the actual achieved compression and expansion ratios, as bwilson4web has indicated. I believe that page EG-3 is saying that the Camry hybrid's effective compression ratio is around 9.8:1, and its expansion ratio is around 12.5:1. But I haven't tried to verify these numbers, and without very detailed information about the geometry it would be impossible to do so.

Stan