Getting airflow data, or RPM info, or something like

Topeka, Kansas, USA
1998 Chevy Tahoe
Well, I've starting thinking again (that can be dangerous) about my charged-air project. It's very nice and stable now. So it's time to think about a next level. Probably a "secondary", turned on (optimally) when airflow rises in the filter compartment. I tried a couple very popular tach sensors a while ago, both showed garbage data alternating with good data. I could imagine getting data out of the mass airflow sensor...if that were practical, which I'm not convinced it is. Or a vacuum switch added with a T somewhere? Or conceivably, something like this:

Thoughts, anyone?
There is an interesting hot wire setup which Rover used to determine incoming air quality/density and it worked very well for such a simple system. Drop the hot wire sensor just after the filter housing and you can measure the air.

Bear in mind that colder air carries more oxygen than warmer air, so an air pressure measurement only tells part of the story but will probably suffice in your application.
Yup. I think that I can go even cruder for now: a microswitch thrown by the accelerator lever. The NO2 folks seem to be doing a lot of that, and I think it fits the situation OK, because Stage 2 needs to turn on a bit off-idle.
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