[nickd]

To reiterate what was mentioned above, the air temperature at the filter is essentially ambient above 10mph (or less). There's no hot intake air to worry about.

Steve Weiner has commented several times that he's measured a 2-3hp gain from the cup car airbox. That's the best you can expect without pressurizing the incoming air.

You can roughly calculate the effect of a ram air intake vs mph. I think the gain is usually less than 5hp at 100mph.

Outside of that, you're getting into changing the intake manifolds and throttle body. That will change the shape of the torque curve but not necessarily add to it.

Exhaust and ignition advance are the low-hanging fruit for the 964. After that, the $/hp is exponential.