You can use tubing as big as you want. 4" wouldn't hurt. It just gets

difficult to fit at some point. I had 4" flexible crap at once,and it

was too restrictive (ie it caused a high RPM stumble) even though the

ridges were very small.

so uve dont this mod before huh? well ill make sure everything is open, and get a couple of holes drilled on the top, and maybe clean it out if it hasnt turned to paper yet ( 20 the years with the same intake ) https://www.nopistons.com/forums/pub...#>/BURNOUT.gif

Well I once had a car with a Holley that I tried various cold air

set ups on. I didn't like the 4" aluminum flex hose, so I moved on

to a "U" shaped box for the air filter. The top of the box was formed

by closing the hood, and the open end was pointed toward the firewall.

I cut a hole into the cowl area (the car was a real beater so cutting

it up didn't bother me) so the carb could draw fresh air from the vents

by the windshield wipers. Of course this is where cabin vent air comes

from..that can be a problem. Anyway it got the intake air temps down

without restriction, and the intake could be heard loud and clear.