For Intake and Cooling systems, Classic Tube offers 6061 Aluminum (16 gauge), .065″ wall in the parts you need to build your custom system:
Straight Length: by the foot (OD 3/4″ to 5″)
Mandrel Bent:

U-Bends (180°) (OD 3/4″ to 4 “)
90° Bends (OD 3/4″ to 5″)
45° Bends (OD 3/4″ to 3 “)

16 GAUGE (.065)

6061 Aluminum Intake/Cooling Tubing

This Aluminum tubing is the least expensive and most versatile of the heat treatable alloys. In the annealed O condition it has good formability for bending. Aluminum is not recommended as an exhaust system material.

For U-bends and J-bends
Determine the Center Line Radius (CLR) by measuring across the outside edges of the bend, subtracting the tubing O.D., and dividing by 2.

Note:
Leg lengths are approximate; usually within +/- .25″. 

Use 5356 filler rod for maximum strength
Use 4043 filler rod for maximum corrosion resistance
Straight Length Tubing

Straight Length Tubing
Straight tubing is sold by the foot, based on the total length of the tubing.
It is cut to the length you specify.
Lengths up to 8 feet can be shipped UPS.