Did the outside air induction cars in 66-69 use 4" or 5" duct to carburetor?



I was thinking of cobbling up a little cool air system just to satisfy myself that it does or doesn't make a difference. Been curious about this for years. I even have some decent boneyard 70's plastics that go from rectangle to round in various diameters to connect to the radiator support.



Good starting point is how the factory did those in-bumper and under-bumper air ducts, but I can't tell from materials I have whether they used 4" or 4" inner diameter ducting?


442 experts, what say you?

 

4" Dia

here's what I made up for my 69
all pcs genuine Olds Parts just from different models / years .

 

4"

 

4" x 31" in 1968-9; 4" x 36" in 1966-7.

 

Nice job"rptw32", as did something similar to my car. I cut off the snout of my factory air cleaner housing, and installed two ovaled 4" ductwork tap collars. Got some quality 4" flex hose from Racer Parts Wholesale(RPW), and ran it to the inner fenders. This hose is actually intended for cooling brakes on race cars, but good high temperature neoprene, and not cheap. RPW also carries a selection of plastic NACA air intake fittings.