Originally Posted by alan_in_tempe

Even if there were enough adjustment range to make an effective Atkinson cycle, you wouldn't get what you want. The benefit of the Atkinson is a larger expansion ratio for the max compression ratio (max compression avoiding pre det).

To reprogram your (and mine!) Seinna's VVT to an Atkinson cycle would only be reducing the compression ratio, as the expansion ratio is already at max for the bore/stroke of the cylinder. Our TCH engine is modified from the Otto version of the same engine for the crank/cylinder config to maintain the desired compression ratio at a reduced stroke while maximizing the expansion ratio at the full stroke.

Note that the modified valving increases efficiency and reduces emissions (thanks to the greater expansion ratio) at the cost of a narrower power bandwidth, and less total power. Fortunately, this is not an issue for the hybrid, with the CVT to (over-)compensate for the reduced power bandwidth, and the electric motors to (over-)compensate for the reduced HP.

-- Alan