Porting the 5532 iron intake manifold

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            Modifying the stock AMC 3185532 cast
iron manifold for increased air flow

By Bernie
Potash

In this
article I’ll explain the way I obtained the maximum air flow using a stock AMC
manifold. Some walls of the manifold were broken through (marked in red) to
obtain maximum flow within the confines of the manifold.
I flowed the
manifold on a Super Flow bench. A special adaptor was used along with a
four-hole spacer to duplicate a carburetor base. I tested drawing through the
bench at 28 Hg simulating wide open throttle. Some might say I need a cylinder
head to be more realistic but just like most cylinder heads are tested and
modified alone with out a manifold attached that’s what I am testing, just the
manifold. The manifold is bolted upside down on the bench, a square of heavy
foam is stuffed into 7 holes and covered with duct tape. Each cylinder is
tested the same way. The bench is adjusted to 28Hg of vacuum and the readings
are taken.  The results for the stock
manifold are below.

  Manifold Stock

  #1

  220

  cfm

  #2

  220

  cfm

  #3

  215

  cfm

  #4

  171

  cfm

  #5

  211

  cfm

  #6

  204

  cfm

  #7

  223

  cfm

  #8

  215

  cfm

From the
data above, the center cylinders do not flow as well as the outboard cylinders
due to the nature of a dual plane manifold. My objective is to build a stout
all AMC street motor including AMC intake and exhaust manifolds. The stock
manifold was designed for a stock head that flows 220-225 cfm at .500-.600”. I
plan on using a ported iron AMC head flowing 240-250 cfm at .600” lift max of
my cam. In order to get that kind of flow from the stock manifold a ton of
metal needs to be removed in the right areas. The size of the ported runners is
1.16” width and 2.20” length to match the heads I will be using. Be prepared spend
a lot of time and remove over a 1 pound of metal! Pictures below of front and
rear cylinders and each pair of ports.

  Manifold Ported

  #1

  256

  cfm

  16.4%gain

            #2

  264

  cfm

  20% gain

  #3

  248

  cfm

  15.3%gain

            #4

  236

  cfm

  38% gain

  #5

  247

  cfm

  17.1%gain

            #6

  246

  cfm

  20% gain

  #7

  277

  cfm

  24.2%gain

            #8

  252

  cfm

  17.2% gain

Big gains
especially the 4 inboard cylinders! This should work well with the iron heads I
plan on using. The areas that I ported through the casting, I use a thin piece
of metal formed to the area and glued on both sides with JB weld. Hopefully
this will help anyone planning a similar project!