CAI: No. Try a warm air intake instead. CAI is good for increasing top-end power, and if you drive like a jerk then the extra air flow could help fuel economy. WAI is more likely to work for someone who cares about fuel economy.
Vortex doohickey: Never. There is not one shred of credible evidence that one of those has ever worked on anything.
Part of the mileage improvement in the VX was due to the smaller diameter intake manifold runners and the smaller diameter exhaust system.
The only reason Honda had to make those changes was because it improved bottom end torque. This allowed a VX to run fine in 5th gear at 1000 RPM. The sacrifice was top end power which was not relevant to high mileage.
If you increase airflow and reduce exhaust restriction you will lose mileage. If that was not true, then why would Honda design and produce (at considerable cost) unique components that were only used on the VX model.
Years ago when I was young & stupid I bought one of those vortex thingeys (Tornado I think) that was placed in the air intake. The only noticeable difference I see that it made, was that it made my wallet $80 lighter.
the idea is to swirl the air coming into the intake. and in some respect, it makes sense but for us it makes none.
we keep the throttle body as closed as possible most of the time so the opening (when open) is very small so if it actually did swirl the air (and that is a big if) it wouldn't matter unless you are closer to WOT.
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I keep my throttle as open as possible, but I doubt it would help me anyway. I doubt that the swirling thing could actually help, but even if it could I doubt you'd get the effect with the small amount of air I'm moving.