The two manifolds selected were McMaster Carr catalog 5469K103 ($16.30), described as Black Anodized Aluminum manifolds with outlets on one side. Two axially located 3/8" NPT inlets, two 1/4" outlets. Each manifold has pairs of predrilled mounting holes on each large face.
DSC05598 of the brass plugs that were found to be ideal to close off the extra 3/8" NPT inlet. When installed the plugs were nearly flush to the end face of the manifold. This allowed both manifolds to be located very close together as shown in picture DSC05630 (above) and DSC05821 (below).
Each 3/16" ID hose barb has a cross sectional area of 0.02761 square inch, thus 2 barbs would have a total cross section of 0.05522 square inch, and 4 barbs (the second battery pack will have 4 Tesla modules) would have a total cross sectional area of 0.11044 square inch. Inlet lines with 1/4" diameter = 0.250" would have a cross sectional area of 0.0491 square inch, while lines with 3/8" diameter = 0.375" would have a cross sectional area of 0.1104 square inch. In order to standardize all of the fittings it was decided to use 3/8" fittings for both battery packs.
DSC05778 showing the manifolds located above the batteries to allow for smooth curvature of the heater hoses. This picture shows the heater hoses inputs (left) and outputs (right) after connection. Gates Corp 5/16" ID rubber heater hose was selected (part # 28408, 50 feet at $51.00). The hose is rated -40' F to 257' F, with max working pressure of 60 psi, and SAE 20R3 Class D2. Gates 1/4" ID rubber hose could not be forced onto the Dorman 800-116 connectors ( https://www.summitracing.com/parts/rnb-800-116 , $57.77 for 12).
DSC05820 with the cooling side end panel installed showing both 3/8" brass connections penetrating through the push in rubber grommets. (7/8" hole with 5/8" ID, McMaster Carr # 9307K65, pack of 10 at $7.63). The manifolds were later installed higher resulting in unused mounting holes that will be welded shut later. Four M6 x 40 bolts fit exactly the predrilled holes in the manifolds.
DSC05821 internal view of the cooling hoses. Note in the foreground the red protective layer of electrical grade fiberglass (GPO3) which covers the top battery module, then a section of 3/4" black foam insulation, and finally a 0.125" sheet of 6061 Aluminum which will be used for mounting the contactors, fuses, and the Orion BMS. For the purpose of this picture, the three layers were pulled away from the end. Normally all three layers would be flush with the edge of the battery module.
DSC05824 showing the tight clearance between the batter module and the Aluminum end plate. The plastic Dorman 800-116 plastic connector can be seen in the very center of the picture (shaded) to the left of the brass 3/8" coolant pipe.