wow nice work
Crabandy, I enjoy and respect your glass work and "can do" attitude.
That airbox on N91CZ is a piece of work, nicely done. Craftsmanship for sure. Assuming this accomplishes a couple things. No appearance of a restriction in air flow from narrowed passage and carb heat on inlet side of filter in case of restriction, therefore the carb heat is the Alternate air. And possibly more airflow through a larger air filter media than the James K&N unit.
I have looked hard at the James fiberglass transition piece that connects the filter to the carb bottom. The side view looks narrowed which it is, top to bottom, but it does widen out to compensate. This version was not Will James's first crack at this and I had to assume he did careful calculations on flow. It appears proper to me in my hand.
Alternate air is another topic. I am VFR only. I pondered the risk and obviously decided it was one I could/would take. That said, the bottom of the transition piece would be an easy target location to install a rotating door with a little glass work as there is ample clearance under it to the cowling.
Pondering here with my thoughts about the induction in general. I looked at a lot of posts here from very creative people. I had lived with a standard Vans air box for hundreds of hours and many condition inspections and repairs. I also learned about the importance of the design and how it came about. Cliff notes here: Vans originally used ram air on the 3 and 4. Once Vans figured out he had a winner of a design and the intake could be a problem he set out to design an intake that would not hurt performance over a ram air setup. Understanding this made me realize the importance of sealing the intake system from leakage both at the nose connection and at the carb heat door while closed. Vans had used the Pressure recovery process of enlarging the air box for the filter media and sized the box for good airflow thru it.
That said I could not see a good transition from the vans air box to the round intake ring of the James Cowling, that I was installing. But I could see Will James had figured it out. I proceeded to build the carb heat flapper door the best I could as far as sealing went and really liked the neoprene seal at the nose better than the Vans baffle material set up.
So, like you....I just did it.....time will tell how it holds up!
I converted from a standard Van Cowl to a James long cowl and plenum and induction system...plus a new paint job. I did not do before and after documentation but had lots of hours flying it. It now is several MPH faster in cruise.
So to quote Tom Cruise from Top Gun..."it is looking good so far"
YMMV.