[blykins]

Larger engines will take advantage of a single plane intake because they can increase the velocity through the intake, so that's not necessarily the issue. A 302 with a Victor Jr can be downright fussy, whereas a 445ci Windsor LOVES that intake and more.

The issue is that when you increase displacement, you need to increase the camshaft duration as well. Cubic inches eat up duration as the cam has more volume to fill.

If you increase camshaft duration to keep the peaks the same, you'll notice that you still have more torque, but the peaks move toward the right and the horsepower will go up as well.

Stroke lets you run easier in a specified range, but also adds more horsepower across the curve. Run your sim again and look at average hp/tq between the 3 combinations.