The Carburetor Shop LLC
204 East 15th
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engine Manifold Selection (heat) Most
aftermarket intake manifolds are aluminum. Aluminum dissipates heat MUCH
quicker than the original cast iron intakes. While on "V" type
engines, carburetor heat may not be necessary, there is MUCH less heat
available for aiding fuel vaporization on in-line engines. Many potential
issues can be eliminated by either selecting an intake with heat provisions,
or fabricating some type of heat provision. If nothing else, a metal tube in
the coolant system attached to the bottom of the intake can be beneficial. Carburetor Selection Since we receive more inquiries concerning 235 Chevrolets, we are using this engine as our example; but the selection process and the synchonization process are independent of make. For best results, the very best thing is to do one’s homework BEFORE one purchases anything. A triple setup MAY have clearance issues. There are several major criteria in the selection of one’s puchase, but the first criteria is how the unit will be used. Consider that 50~60 years ago, triple carb manifolds were sold for RACING! Today, while a very small percentage will submit their vehicles to the race track, most are interested in triple carbs for either LOOKS ONLY, or looks with a modest increase in performance. These two uses have vastly different requirements in carburetors. Typically, the manifold sold in the period
would be drilled for three carbs the same size as the original (a 216
Chevrolet would have 3 S. A. E. size 2 carbs, whereas a 235 Chevrolet would
be drilled for 3 S.A.E. size 3 carbs). By using this arrangement, the user
could order two addition original carburetors from the dealer to go with
original carb on the engine. At the same time, the user would install a
full-race cam, a magneto ignition, headers, high-compression pistons; all to
go with a numerical higher rear-end ratio BECAUSE THE ENGINE WOULD HAVE AT
BEST A VERY HIGH IDLE, AND VERY LITTLE LOW END TORQUE. This is a good
selection for a trailered race car, but a poor selection for the “cruiser” on
the street. The second criteria is to decide if solid
linkage, or progressive linkage will be used. We highly recommend solid
linkage unless this is strictly a “show” item, and the outer 2 carburetors
will be “dummys” (in place for “looks”, but not used). The reasoning for this
recommendation is really quite simple. If one uses progressive linkage, then
the center or primary carburetor must be of sufficient size to idle well, and
run the engine well at normal cruise RPM. Since the manifold is designed for
three carburetors, the runners to the outer cylinders will not deliver the
same A/F ratio as to the center. To prevent a lean A/F ratio on the outer
cylinders, the primary carb will have to be artificially rich, thus reducing
fuel mileage. For performance work, it is very difficult to get the end carbs
to come in without a lag of a third to half a second. If the reduced fuel
economy and the lag are acceptable to the enthusiast, then progressive
linkage may be used. Carburetor selection for progressive linkage is easy.
Simply use 3 of the original carbs for the engine. I am not saying that
progressive linkage won’t work, as many use it. But it cannot work as well as
solid linkage. Did you ever see an XK-E or Healey 3000 with progressive linkage?
Or the triple YH setup used on the early ‘Vettes? Since the manifolds of today are basically
copies of the manifolds of yesteryear, generally the street enthusiast will
need to modify the manifold for smaller carburetors. Example: for a stock or
modestly built Chevrolet 235, an enthusiast might choose 3 original Carter
W-1 carburetors as used on the Chevrolet 216. These will be marginally on the
large size, but can be dialed in without too much effort. A better choice
(but possibly more difficult to find) would be the Carter WA-1 carburetors
used on the small (202 CID) Husdon in the early 1950s. Two were used on the
Hudson; three work well on the 235 Chevrolet. Still better, but much more
expensive, would be the carbs used on the Willys 134 CID 4 cylinder. Carter
W-0 and Carter YF carburetors were used. The key in selection is to choose
carburetors that are individually too small for the engine. The manifold
would be drilled for size 3 carbs (2 15/16 inch mounting pattern), but the
216 carbs and the Hudson carbs are size 2 (2 11/16 inch mounting pattern).
There are three methods of doing the conversion: (A) use size 3 to size 2
adapters (extra cost, and looks “hokey”); (B) slot the holes in the
carburetor (no additional cost, but looks even more hokey); or (C) have a
good welder fill the original holes in the manifold, and then drill and tap
for the correct size (extra cost, but looks much more like a factory
installation, and weren’t looks the major criteria?). If you plan to use on a trailered racecar,
use the larger size. The third criteria for selecting carburetors
is that the EASIEST AND LEAST EXPENSIVE good results will be obtained by
selecting either (A) carburetors which were originally designed for used in a
multicarb environment (example: Carter WA-1’s used on the Twin-H Hudson) or
(B) carburetors with a mechanical (as opposed to vacuum) power system.
Carburetors with a vacuum power system may be used, but the tuning MAY be
more difficult. If you have a spring winding kit and feel comfortable hand
winding small precision springs, you may ignore this paragraph. The Carter
W-1 units have a mechanical power system, and the Hudson WA-1’s were designed
to run in a multiple carb environment. The next criteria is the one that gets the
most arguments – the brand of carburetor to use. After almost 60 years of
working on carburetors, we recommend Carters for most applications (readily
available, reasonably priced, and parts readily available). For the high end
user to whom cost is not an object, but perfection is the goal, we suggest
either Strombergs are Zeniths. Other brands may be used, but there are no
others that we recommend. In any event, one should choose a brand with which
the user or the mechanic of the user is extremely familiar. In any event, ALWAYS
use matched carburetors by tag numbers. Trying to use non-matched carburetors
is simply asking for trouble. If you start with used cores, acquire good
rebuilding kits (we would suggest the ones we make); and rebuild the
carburetors to absolutely stock calibration. By building to the stock
calibration, you build a repeatable “baseline”. Calibration adjustments, if
necessary, may be made later. One issue that MIGHT be of concern is
manifold type. The types are the common plenum type, and the individual
runner (IR) type. The IR type will require SIGNIFICANTLY LARGER carburetors
than the plenum type for the same engine. Once the carbs are rebuilt (or new carbs),
one is ready for the installation and synchonization procedure, which is
independant of brand, type, and size. Solid linkage will be required (unless
you have some funky home-made manifold that has both carbs feeding into a
centrally located plenum). Progressive linkage is not an option. Synchonization (solid linkage) |