If you want to see something, and your car uses a carburetor system then unbolt the carburetor, put a fine stainless steel mesh on the inlet, and bolt the carb back on top, ensuring the gap between the inlet manifold, mesh and carb is sealed up to prevent air leaks.
A drop in performance will be noted, but fuel use will be down as the air/fuel gets mixed properly before it enters the engine.
Can't vouch for it, only heard from somebody who tried it as he got gautvol of bolts falling into his carb and messing up his engine. (he had a souped-up engine).