new 03 january 2019

44 IDF plenum construction

this is sort of TMI but what follows is fairly detailed construction of the plenum that bolts to the modified trough plate. it may seem a bit silly, that it would have beensimpler to simply cut a new trough plate from say 3/8" aluminum and bolt the carb on; but the trouigh is not wide enough for the carb base, so it would need a riser plenum anyway. i wanted the plenum to empty into more or less a single point as does the single carb, as i didn't want to mess with the basic fluid design of the intake system. and the factory trough plate is pretty.

the two 44mm bores (1.73") are larger than the WCD ("Rochester 2G") trough plate bore area. i milled out a WCD trough plate to the same area (approximately 4.6 square inches) and fabricated a steel plenum to transition two 1.75" tubes into the single rounded-rectangle hole in the trough plate (very roughly 3.5" x 1.5") as smoothly as possible. the steel plenum was pinned to the trough plate then blended smoothly. the big hole precluded using the original mounting studs so recessed socket head bolts fasten the trough plate to the head and four socket screws bolt the plenum to the trough cover.

after doing the math and drawings on the port areas the plenum was roughed out, since it was the gating item for all that follows. the tube is odd sized to get the desired 1.75" ID. i had to buy the whole 10-foot length to get the 6 inches needed here.

the trough plate was milled out at this time. it was kind obvious that the original mounting studs were not going to be usable.

smoothing and blending was where all the work was. the lower end of the tubes had to be shaped partially squared to meet in the middle. lots of tapping, but i'd already calculated the area so it matched the pre-cut steel flange tha mates to the trough plate, which was a tiny amount undersized so i'd have room to match the aluminum to the steel.

i got nearly all of the smoothing done in steel; i ended up using a small amount of JB Weld which according to the always-authoritative internet (...) seems to hold up in this application.

once the steel plenum was made and shaped the rest was straightforward. the Redline Jeep kit YF adapter is 2" high, this one is 3". i wanted it shorter but that made the tube-to-flange angles troublesome so i increased height. i lose some hood clearance but the air cleaner will be mounted inside an airbox attached to the hood, not the carburetor.

the carb itself got some working over. the booster venturis were usable out of the box, but the aluminum castings benefit from some hand attention not feasible at the factory. the venturi castings were rough on the leading and trailing edges, with ground-off sprue stubs and other rough stuff. not visible here is that the internal passages in the fuel feed from the bowls are internally rough, with flash partially occluding the port. these got attention via magnifier and tiny needle files.