I am in the process of converting a 3.0 Mercruiser to replace the Chevy 153 in my '47 CJ2A. I'm making an exhaust manifold out of a set of SBC hugger headers, which seems pretty straight forward. I have a 2-1/2" 16 gauge U-bend which I'm planning to use as the basis for an intake manifold. But I have a few questions for you more experienced folks going in:
1. Most of the factory 4 cylinder manifolds I've looked at while searching for something I could adapt have a "box" area directly under the carb with smaller channels or tubes connecting that to the flange. Is there as reason for the extra volume directly under the carb? or could I just mount the carb to a plate on top of the U-bend? I will need to press the ends into more of a rectangle where they meet the flange to line up with the shape of the ports. I could weld up a "box" to mount the carb on, but that makes the fabrication more complicated. A big part of my challenge here is getting the intakes in-between the exhaust tubes.
2.I'm planning on running the two barrel marine Rochester, (with a couple of minor mods like a vacuum port and a manual choke), How much effect does the orientation of the carb have on performance? I mounted the Weber 32/36 perpendicular to the head on the 153, and it works well, but I did that primarily because it is progressive and I drive most of the time on the 32 mm barrel so I didn't want it biased toward the rear intake port. The Rochester is not progressive so would it make any difference if I mounted it parallel to the head? That makes the linkage much simpler, and helps a bit with fitting it in between the exhaust tubes.
