3" aluminum flex duct about $3.99 at most stores that carry hot air heating
stuff this stuff. One piece will stretch out longer than you'll ever need
for 1 car.
It can be ovalized to fit the air flow box on 405s, will make real tight 90
degree
bends and is fire and oil proof. I can't imagine anything better.
It is also available in otheer diameters.
Bob Bruce