Here's a photo of my choice if you don't know what I'm talking about:



When I received my new ecz B manifold the other day, it had the plastic spacer. I had already bought an aluminum one on ebay. I assume the plastic one would insulate the heat better. Is the aluminum spacer superior in any way?

As you've indicated, the original phenolic plastic spacer should be a better isolator of the carburetor from intake manifold heat than the aluminum spacer.  It's interesting that both 1/2 inch spacers were used on different FoMoCo vehicles.

Once upon a time, in using a later 1.12 Autolite 4100 carb on a 'B' manifold, I found that the 1/2 inch thick aluminum spacer worked well as a carburetor to intake manifold adapter.  Using a file, I tapered the throttle bores of the aluminum spacer so that the larger carb throttle plates would open. 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

I'm using a phenolic spacer on mine for better heat isolation and because I thought that was the way the 4100 was originally installed.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

The aluminum is the way to go should you decide to drill it for a large vacuum nipple for a PCV setup. I found an aluminum nipple on an old ford factory oil cooler, cut it off, then tig welded it into an appropriately sized hole I bored (back/ center) into the spacer. Can't do that with phenolic, obviously. To address the greater heat transference, I  chucked an 3/32"  drill into my drill press, and utilizing the depth stop to prevent "thru bore", I carefully "swiss cheesed" the spacer top to bottom. Works like a champ, and won't deteriorate like phenolic does.

BOO- YA!!!

When I installed a 2" plastic spacer under my  Holly DP I could feel the increase in TQ
and no clearance issues under a '54 Ford hood
giddy up, Carson

Thanks everyone. For now I think I'll use the phenolic and I'll keep the aluminum as the backup, or as a mod spacer if I need one.