Here is the progress on my RV-4 cowl so far. The hinge pins are not
installed, so the top is just laid on. The last two photos show the
rough fitting of an air filter. It is a work in progress, I know it is
not at big as I'd like, but there's only so much I can fit into this
cowl. I supposed that I could put the throttle body on the rear end of
the manifold, and have quite a large space to fit air filter elements.
We'll see.

Brian Trubee

Looking good brian. You could take a mold off that thing and
rent it out to other RV4 builders.

Paul Lamar ...No rotor no motor.

I think it looks very good.  The single flap looks good too.  If it
performs on a par with multiple louvers , then I think it is
preferable.  Paul?       Jerry

On an RV4 a single cowl flap will work great.
All depends on the slope of the bottom of the cowl.
RV4 are almost flat.