Some aftermarket manifold pics...

Okay guys, here's the deal on that open plenum factory intake. First, it is cast iron, not aluminum. The pics may look kind of like aluminum, but it is just the surface color after glass-beading.

http://www.directimagehost.com/is.ph...RD_noflash.jpg
Note the plenum has been machined out; it is not cast without a plenum. Also, note the odd (for AMC) provision for choke heat. It is designed like the GM divorced choke configuration where the bimetal spring was bolted to the manifold with a rod that actuated the the choke mechanism on the carb. Could this be for a (gasp!) divorced choke Holley carb????

http://www.directimagehost.com/is.ph...RD_compare.jpg
This picture has the oddball manifold in the center with a early 390 manifold on the right and a Machine manifold on the left. The oddball manifold is more like the early 390 manifold (736 casting) than the Machine manifold. The carb mounting pad is the same as the 736 manifold, the bolt holes are for the early heads and the general appearance is the same.

http://www.directimagehost.com/is.ph...g=RD_choke.jpg
Closeup of the choke heat sink casting.

http://www.directimagehost.com/is.ph...ing_number.jpg
This is the biggie. This is the casting number that has been ground off. What ever was there began with "31" and was later stamped with "9"s in the last 3 positions. Note that the casting number is in a different place than all other cast iron manifolds I have seen. It is on the top of the runners directly behind the carb mounting pad, like the R4Bs with the factory number.

http://www.directimagehost.com/is.ph...mg=RD_rear.jpg
This is the area on the rear of the manifold where the casting number usually is located. Nothing there. For those of you who are wondering, there is NO number on the bottom of the manifold. Note that the numbers on top of the ports where the manifold meets the head are larger than used on the other manifolds.

Any ideas? Maybe a TransAm development piece? Any takers? I would be willing to trade for an unmodified Machine intake, or I maybe for one of the 736 manifolds with the oblong holes on the plenum where the carb mounts.

Fella claims this is an AMC factory iron squarebore, whatcha' think?
Original Intake for the 390 4bbl AMC?

Looks like a variant of a spreadbore to me since the primaries are smaller.
It's for sale if anyone is interested.
http://frontier.net/~mystkblu/amcsqboreintake.jpg

Elliott -

That's a '73 or '74 360-401 manifold for use with a 4300 series Autolite carburetor. Actually, all the square bore manifold had slightly smaller primaries than secondaries because all the factory AFBs and 4300 Autolites had smaller primaries than secondaries. The difference in size was not as dramatic as the "spreadbore" carburetors.

That manifold is for a 71 or 72 thru 74 360 or 401. Not sure of the first year for EGR valves. Definitely not for a 70, although it would fit, just a plain old 4bbl smog manifold.....

Tom