Intake Manifold Design
In the past couple articles, I discussed the design aspects of the various engine blocks and cylinder heads, and in this MM issue we’ll cover intake manifolds.
Words: Larry Shepard
In the past couple articles, I discussed the design aspects of the various engine blocks and cylinder heads, and in this MM issue we’ll cover intake manifolds. You will note that I specifically used the word intake manifolds rather than induction system because I feel that induction brings air flow to mind and that leads to carburetion or throttle bodies. While the carburetor and/or throttle body is closely related to the manifold, they make the discussion too large for a single column. Therefore, I will focus on intake manifolds. Additionally, today most I-4s and V-6s are multi-point fuel injected (MPI), so manifold swapping isn’t often done. I’ll stick with V-8s.
In the typical V-8, the intake manifold covers the top of the engine. This feature is extremely important for crate engines, which are typically shipped with the intake installed—or any engine that must be stored or shipped prior to installation. Each intake manifold is unique to a family of engines, like the A engine or B engine, and generally can’t be swapped from one family to another. While manifolds can generally be swapped within an engine family, there are exceptions that I’ll cover shortly. Blocks can be decked and over-bored and heads can be ported and have bigger valves installed but intake manifolds tend to be installed as received. The design aspects are included in the casting and basic selection. In the last few years, fabricated manifolds are readily available but they are expensive and should be dyno-tested for fuel distribution before they are installed onto the vehicle.
In general, a 7-digit casting number is used to identify the various production intake manifolds. This number is usually located on the top of the manifold, on one of the forward runners. There is a very good list of production casting numbers in the 2009 Mopar Performance catalog, or for information you may contact the Mopar Direct Connection Tech Line at 1-888-528-HEMI (4364). Intake manifold castings tend to be made in one of three materials: cast iron (mostly production versions), aluminum (most aftermarket/performance versions) or magnesium (only one to date). Many current I-4 and V-6 engines use plastic, but this material isn’t popular for V-8 parts.
While the casting number tends to yield the most detailed information, the most obvious design characteristic is the carburetion aspect—2-barrel (bbl), 4-bbl, 6-bbl or 8-bbl—which is simply the number of throttle bore holes in the top of the manifold. An MPI version has one extra hole per cylinder along the attaching rail—typically on top. The design feature that is important to consider is the width and the best example is the B and RB engines. These two engines use the same cylinder heads but the two different deck heights (the B is 9.98" while the RB is 10.72") causes the RB (413/426W/440) intake like P4529462 to be much wider than the B (361/383/400) intake like P4529463.
The next design feature to consider, is the size of the ports, and the best example is probably on the RB engine between the standard heads and the big-port Max Wedge heads used on the ‘62–‘64 Max Wedge engines. These heads are now readily available – new. The Max Wedge single 4-bbl intake is P4876337 (similar to the one listed above in width but with much larger ports). The MW ports are so large that you can’t port-out a stock manifold to the Max Wedge size and if you installed the standard manifold (standard-size ports) onto the Max Wedge heads, the ports are uncovered. Using welding to add material to a standard manifold so it would seal is expensive because the welded manifold must be re-machined or it will never seal. The more common example is the small-port 318 and the large port 340/360 production manifolds. This switch does not cause the sealing problem, so it can be done easily. All of the aftermarket manifolds use the larger 340/360 style ports.
One design feature that is made into the basic manifold is its basic plenum-runner configuration. There are two basic styles: dual-plane and single-plane. On a V-8, when all 8 runners come into one common plenum the result is defined as a single-plane. On a dual-plane manifold design, four runners join in one plenum and the other four runners join in a second plenum. One group of runners sits on top of the other creating dual (two) planes. Typically the two plenums sit side-by-side in the center and have a divider down the center that separates the two sides. Dual-planes are good street manifolds, while single-planes are used in racing. There are exceptions and lots of over-lap. The 340/360 4-bbl dual-plane intake is P4876335 while the standard head 340/360 single-plane is P4876334.
Generally the carburetor sits on top of the manifold so it is easy to identify the basic carburetor package that it was designed for—2-bbl, 4-bbl, 6-bbl or 8-bbl. By far the most popular intake manifold is the basic single 4-bbl. While there were some actual 2-bbl intakes used in production, today if you want to use a 2-bbl carb in performance application, you tend to use a 4-bbl intake with a 2-bbl adapter.
That way, you have a much bigger manifold selection. One of the most popular packages is the 440 6-bbl intake, P4529056. The 340/360 6-bbl (only built in 1970) uses manifold P4529054. The 383 B-engine 6-bbl is P4529055 while the 426 HEMI® 6-bbl is P5153738. These last two 6-bbls are not production-based—only available from Mopar®. While the 6-bbl system used three separate 2-bbl carbs, the 8-bbl system uses two 4-bbl carbs. The most popular or common 8-bbl system was used on the 426 HEMI from 1966 through 1971. There are actually two versions: the AFB carb intake is P5153737 while the Holley carb version is P4510633. Both are considered in-line systems.
About the only machining that is generally done to an intake manifold is called port-matching. It makes the ports in the manifold match up to the ports in the head. The intake manifold gasket is generally used as the template. The intake manifold is relatively easy and quick to change. All you need is the new intake and gaskets. There are four areas that the gaskets have to seal: left and right sides, the front, and the rear. The front and rear seal to the block (tappet chamber) and the two sides seal between the manifold and the head. The sides seal air (in port runners) and oil while the front and rear seal oil. The thickness of the intake side gaskets can be used to help the vertical alignment of the manifold ports to those in the head. This is the reason for multiple gasket thicknesses offered to service a given cylinder head style.
One of the unique aspects of the B-RB engine manifold is that it uses a breast-plate for an intake gasket. The breast-plate is made of stamped steel and fits below the intake manifold itself. The B engine (383/400) gasket is P4286825 and the RB gasket is P4286826. Since the breast-plate covers the engine’s tappet chamber, the breast-plate also keeps hot engine oil off the bottom of the manifold. The 426 HEMI does not use the breast-plate style of intake gasket and therefore adds a heat shield, P4529431, to the under-side of the manifold. It is designed to keep hot oil off the bottom of the intake manifold. Only the Mopar 4-bbl and the two 8-bbl in-line manifolds have this feature, but it should be added if possible.
There is no water in the intake manifold as used on the B, RB, 426 HEMI (Gen II) and Gen III HEMI. However, there is a water cross-over at the front of the engine on both the small blocks—A-engine and Magnum.® This water cross-over connects the two heads and also serves as the thermostat housing.
Caution: there are two styles: a large one that is centered, as used on the 1978 and older small blocks, and a smaller one that is offset to the passenger side—used on the 1979 and newer small blocks (A and Magnum). There may be variations of this timeline in aftermarket/performance manifolds. Note: the B, RB and 426 HEMI use the big thermostat.Tip: for custom engine installs, the 90-degree thermostat housing, P5249191, may be helpful because it has three positions allowing you to point it straight at the radiator inlet. Another unique feature of the small-block manifolds and the water cross-over passage is that it has a very large, and short by-pass hose, P4876373, and a short, stubby fitting, P4876374, that fits into the front of the manifold. This fitting can be very difficult to remove and it is much easier to install a new one.
All the 5.2L and 5.9L Magnum engines (approx. 1992–2003) were produced with MPI. If you want to install a 4-bbl MPI based on a hi-flow single-plane intake onto the Magnum engine, you can use intake manifold P5007398AB with install kit P5007638. If you want to install a 4-bbl carburetor onto the Magnum engines, use P5007380AB (single-plane). The Gen III 5.7L HEMI production engine also uses MPI so if you want to install a 4-bbl carb, use P4510581 (SP) or 8-bbl in-line P5153556. With either manifold, you want to add PCV adapter kit P5155005. Note: other V-8s like the 426 HEMI, A, B/RB and Magnum use the valve covers for fitting the PCV.
There are issues with manifold attaching bolts relative to length so always install the attaching bolts that are going to be used into the manifold on the workbench to check the amount sticking out below the manifold face. The tricky one is the A-engine W2 4-bbl single-plane like P4529408AB versus the standard port A-engine single-plane P4876334. The oval ports on the W2 are obvious but the much larger ports also push the attaching bolt spacing further apart, based on the divider between the ports. This makes the two inside attaching bolts on each side hard to install so that a small-head bolt may be required to be able to get it into the flange and get a wrench on it to tighten it. Be sure to check this on the bench – first.
With all intake manifolds there are carburetor throttle linkage issues. Most common hardware works for the 4-bbl carbs but you will need the 6-bbl linkage kit P4529061 for the 6-bbl carbs including the HEMI 6-bbl, and there are two cross-ram linkage kits – P5153567 (Max Wedge) & P4510635 (426 HEMI).
For restoration applications, appearance is very important and the intake sits right on top so it must look like the original production units. The 340 6-bbl and 440 6-bbl intakes are listed above. On the pseudo-resto side, the dual-plane 383, P4529117, and the dual-plane 340/360, P4876335, could come close to looking like production units with paint. The 1962–64 Max Wedge cross-ram intake (aluminum) and the aluminum and magnesium 426 HEMI cross-ram intakes (resto versions) are available from A & A Automotive & Transmission Repair www.aandatrans.com. Also available for performance applications are a take-apart aluminum 426 HEMI cross-ram P5007534 and a one-piece, aluminum Max Wedge cross-ram, P5007330.
More intake manifolds and part numbers are being added to Mopar’s lineup. For additional applications, please refer to the latest Mopar Performance catalog or visit www.mopar.com. Space limits my discussion; if you have specific questions, please call the Mopar Direct Connection Tech Line at 1-888-528-HEMI (4364).
