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The A-engine and Magnum intake manifolds are not interchangeable without modification. The aftermarket offers intake manifolds that are machined with a dual attaching bolt pattern. However, almost all factory and aftermarket manifolds are machined specifically for the Magnum engine with vertical attaching screws or A-engine with perpendicular-to-head-face attaching screws. One unique aspect of the two related engines is that all Magnum production engines are fuel injected (multi-point injection or MPI) and most of the A-engine manifolds are carbureted. A few A-engine versions were sold in the mid- to late 1980s and early 1990s with 318 and 360 engines that used throttle body injection. These throttle bodies were small 2-barrel units and did not lend themselves to performance applications.
Production Intakes
The A-engine family has had a very wide range of intake manifolds, from small 2-barrel units, to 4-barrel units (both AFB and AVS) and large spread-bore 4-barrels (mainly the Carter Thermo-Quad), and the 6-barrel. In addition, the aftermarket has offered tunnel-rams (2- and 4-barrels), cross-rams (2- and 4-barrels), and many other options.
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All A-engine production intake manifolds are made of cast iron except for the 1970 6-barrel, which was cast in aluminum. All Magnum manifolds are made of aluminum. The 340 and 360 4-barrel manifolds are good manifolds for torque and power. The 318 4-barrel manifolds (1978–1989) are basically unchanged 360 versions.
The first couple years of 273 production used vertical attaching screws, so they are unique. All other A-engine intake manifolds are interchangeable. To identify an intake manifold, say the 2-barrel versus the 4-barrel, the vertical attaching screws are easy enough to spot, If you want to tell a 1972 340 4-barrel intake from a 1974 360 4-barrel intake, I strongly recommend using the casting numbers, which are on the top of the intake and easy to see, even with the manifold installed. Both of those intakes used spread-bore carburetors (ThermoQuads), which are easy to differentiate from the 1968 340 4-barrel, which is not a spread-bore design (it has huge secondaries).
All production manifolds have easily visible casting numbers. Aftermarket manifolds tend to use logos, such as 'Edelbrock' or 'Indy.' Manifolds designed by Mopar Performance typically have the 'Pentastar' and/or the 'Mopar' logo.
Although the Carter AFB and AVS were the most popular production 4-barrel carburetors, most of the popular aftermarket aluminum 4-barrel manifolds have both the Carter and Holley attaching bolt patterns. Edelbrock offers an adapter so the AFB/ AVS/Holley carbs can be mounted on spread-bore manifolds, such as ThermoQuad versions. It also works in the opposite direction, to adapt ThermoQuad or spread-bore Holley carbs to the AFB/AVS/Holley-style manifolds.
Unlike many production engines, the 340 and 360 cast-iron dual-plane OEM intake manifold is a very good piece, and for a long time, the aluminum dual-plane was only slightly better. The Mopar Performance aluminum dual-plane was the first step forward. Edelbrock's high-rise dual-plane is the best one today. In addition, Weiand offered an aluminum dual-plane intake for the W2 heads, which was a good option for street/ strip use but availability is an issue.
Many aluminum single-plane intake manifolds have been produced and the Offy Port-O-Sonic was the original best, especially for manual transmission use, and the Holley intake was as good for the automatic and more user-friendly. The only real advance on this situation is the Mopar Performance intake, which is now the best single-plane. That statement only applies to stock cast-iron heads.
Dual-Planes
The aftermarket aluminum dual-plane intake is much better at making power than the production versions, but this advantage is not true of the typical Chrysler intake. With the A-engine, the cast-iron production manifold makes about the same amount of power, but the aftermarket aluminum version is easier to work with and is lighter.
The 1970 6-barrel aluminum intake manifold is also a dual-plane design and uses three Holley 2-barrel carbs. With 318-style small intake port heads, you are still better off to use the 340/360 large runner intakes even though the ports do not line up. Use 340/360 intake gaskets in this situation.
The original W2 intake was a single-plane design, but several W2 dual-plane intakes were produced in the 1990s and early 2000s. There were no dual-plane manifolds built for the race heads such as the W7, W8, and W9.
Single-Planes
For many decades, the single-plane intake has been the race manifold and the horsepower winner. But a lot of research and development has taken place to create single-plane high-performance street manifolds. The original 273 manifolds were single-planes, but they were a long way short of the 340 and 360 manifolds.
The first of the single-plane horsepower winners was an Offenhauser Port-O-Sonic, but it needed a lot (at least four) of fuel distribution dams in the plenum. Next was the Holley 4-barrel intake manifold, which was the best for automatic transmission cars. The original W2 single-plane made good power with W2 heads. The next step up was the introduction of the Mopar 340 single-plane, which was the best 4-barrel intake at the time. Next came the influx of big-port high-flow cylinder heads, so Mopar introduced a race version of the 340 single-plane. It had bigger and taller ports to work with the bigger port in the heads, such as the W5 and the W7. This was the horsepower champion but without the big ports. The original Mopar single-plane is a better choice.
The W9 equipped with the best manifolds was designed as a CNC- ported head, but there is one version that may have the best as-cast port ever produced. The intakes designed for the W9 heads were designed to work with this head (or the bigger CNC-ported versions) and were leading-edge technology at the time.
Mopar Performance made all of these intake manifolds. Also, with the race intakes, such as the W9, watch for the two deck heights used in the race blocks: standard tall, 9.56/9.60-inch, and short 9.0/9.2-inch manifold width changes.
Throttle Body Injection
The intake manifold used a throttle body injection system from 1981 through 1991 on the 318 engine and from 1989 through 1992 in the 360. This type of system works more like a carburetor than the newer MPI system used on the Magnum. For any performance application, remove this system and install a 4-barrel carburetor (and manifold) or the Magnum MPI system.
Magnums
All the Magnum engines (1992– 2002) use the same aluminum intake manifold, and there is no big port/ small port model. The standard manifold is large and shaped like a beer barrel. These manifolds also have a bolt-on breastplate on the bottom of the intake casting designed to keep hot oil off the runners.
The key issue with Magnum intake manifolds is that all Magnum engines were MPI fuel injected. Also, Magnum heads use vertical intake manifold attaching screws, while A-engines use attaching screws that are perpendicular to the cylinder head's intake face. Intake manifolds are not interchangeable between Magnum engines and A-engines. The A-engine manifolds could be adapted by welding, but it is expensive and new manifolds are readily available.
The stock beer-barrel Magnum intake manifold is fine for stock applications, but it should be replaced for any performance project (except NHRA Stock class racing where the stock casting is required). The Mopar Performance 2-barrel single-plane intake P5007398 is a suitable replacement. It makes more mid-range and high-end performance, allows use of factory accessories, and is the same height as the stock manifold. Use installation kit P5007638 to help make the swap more user-friendly.
The stock 2-barrel throttle body flows a lot of air because it doesn't have to meter any fuel but performance customers lean toward 4-barrels. This swap requires a 4-barrel intake manifold. Do not install a 4-barrel throttle body onto any of the 2-barrel intakes. The 4-barrel aluminum single-plane intake for the Magnum heads is P5249816 for the right-hand linkage used on trucks or P4876615 for the driver-side linkage used on passenger cars. These manifolds come with a 2/4-barrel adapter so that either the production 2-barrel throttle body or an aftermarket 4-barrel throttle body can be used. The intake runners on these two intakes are slightly larger than on the replacement 2-barrel intake discussed above and, therefore, make a small increase in power over the 2-barrel intake using the 2-barrel throttle body.
All muscle car engines used a driver-side throttle linkage. The Ram trucks that received Magnum engines use a passenger-side throttle linkage. To convert an MPI Magnum to carburetor usage, the intake manifold has to be changed along with replacing the throttle body with a carburetor. In the mid-1990s through the early 2000s this swap was popular because Mopar Performance was selling Magnum crate engines converted to carburetor usage.
To convert a stock Magnum engine, you need a 4-barrel intake manifold (P5249501, single-plane) designed for use with a carburetor. It has the Magnum's vertical attaching screws, and the 4-barrel carburetor pad that fits the dual pattern for Holley or Carter/Edelbrock. When converting to a carburetor, you must have either a mechanical fuel pump or a fuel pressure regulator in the system for the carburetor to function properly.
Aftermarket Intakes
All aftermarket intake manifolds are made of aluminum, but that is about the only feature that they share. There are dual-planes, single-planes, race single-planes, 6-barrels, 8-barrels, and even supercharged versions. There are standard, W2, and Magnum port versions. Availability is constantly changing, so double-check any part with the latest information on what is in stock, what's new, and what has dropped from sight.
Dual-Planes
Edelbrock made the original dual-plane, aluminum intake manifold for the 1968 340, called the LD-340. It's now called the Performer 340/360 (revised and updated). This is a good manifold and was the standard performance part for many years. The trick with aluminum dual-plane intakes to make more power for performance projects is to mill down the divider between the driver's and passenger's sides. This trick works with any dual-plane.
The Edelbrock Performance RPM 340/360 makes more power than the standard Performer because it has somewhat larger runners (1.01 x 2.17 versus .97 x 1.95 inches) and is taller or has a higher rise (raised by about .75 to .72 inch actually).
The RPM Air-Gap 340/360 is the next intake on the performance ladder. It has about the same height and uses similar runner size as the Performer RPM, but it has a plate cast across the bottom of the manifold that keeps the hot oil off the bottom of the intake runners. Thus, it creates an air gap between the bottom of the manifold and the bottom of the intake runners. Edelbrock makes the RPM Air-Gap Magnum, and at this time, it's the only known aftermarket dual-plane for Magnum engines. It is designed for use with carburetors.
Single-Planes
Single-plane manifolds used to be considered a race-only component; low-RPM throttle response was quite poor because engines typically load up on fuel. Improved designs have now made the notion no longer valid. Edelbrock offers the Torker II and the Victor for standard 340/360 rectangular-port heads and a Victor W2 for oval-port heads. It also offers a Super Victor, which is an air-gap design and is about 1.3 inches taller than the Victor. Indy Heads offers large-port (and tall) single-planes for standard rectangular-port heads, along with 6- and 8-barrel two-piece single-plane manifolds in several versions.
Multi-Carbs
Several manufacturers offer multi-carb intakes for Mopar big-blocks, but only Indy Heads currently offers a two-piece, aluminum single-plane intake manifold for use with the 6-barrel (three 2-barrels) and the 8-barrel (two 4-barrels).
Tunnel Ram and 4500
The typical tunnel ram intake is designed for using two 4-barrel carburetors in-line; the 4500 is the largest single carburetor offered by Holley and Quick-Fuel. The 4500 does not fit the standard Holley 4-barrel carb pad attaching pattern. These manifolds have been made as castings in the past but are probably fabricated today. Indy Heads offers a 4500 cast manifold.
Fuel Distribution
With any carburetor system, fuel distribution issues are common with the intake manifold, whether cast or fabricated. These problems can be identified by using a dynamometer. The solution is always to put dams (wooden popsicle sticks) in the floor of the plenum. It is an issue with single-plane intakes but is not an issue with dual-plane intakes. Chrysler/Mopar used to provide this information (where to put the sticks), but hasn't done so for the past few years.
Fuel distribution is the basic problem. When you run an intake and carburetor on an engine, all eight cylinders do not receive the same amount of fuel and air; some are rich and some are lean. In general, the overall fuel level is adjusted upward until some cylinders are on longer lean, but that leaves the few rich cylinders. If these cylinders can be brought down to the proper fuel/ air ratio, the engine makes more power. This is one aspect of dyno testing that can be a real bonus with any single-plane intake manifold.
Manifold Selection
Because of the many possible choices this is almost as difficult as selecting cylinder heads and camshafts. Popular manifolds are kept in circulation while unpopular manifolds are dropped from production; availability is constantly changing. The same is true for cylinder heads. In addition to all that, fabricated manifolds can be expensive.
The dual-plane is the best street manifold and the Mopar Performance dual-plane has been the best of them. The Edelbrock Performer RPM has larger runners, makes more power, and is definitely the best choice for larger displacements, such as 390 to 400 inches.
Magnum
The best MPI intake for the Magnum is the Mopar Performance design. The traditional aftermarket doesn't offer many MPI manifolds so most of these options are based on the Mopar Performance line. Also, many MP manifolds have fuel-injected bosses (not machined), which can be machined for fuel injectors. Edelbrock and Mopar both offer carburetor versions; a tie.
Single-Plane Intake for Carter AFB/ AVS and Holley 4-Barrel The single-plane is basically a race or horsepower manifold with the possible exception of 390- to 400-ci engines. The two styles of standard 4-barrel carburetors (the Holley and the Carter) work well on the single-plane. The Mopar single-plane is overall best, but the race version is best for ported-head engines and larger displacements. If this manifold isn't available, the Edelbrock Super Victor (air gap) is best.
6-Barrel: Only the standard manifold is available from Mopar. For larger displacements and/or ported-head engines, the Indy Heads two-piece would be interesting. 8-Barrel: Today's choices are limited, but the Indy Heads 2 x 4–barrel intake looks interesting for larger displacement engines.
Manifold Prep
Chapters 1 and 5 discuss various milling ratios: deck, intake face, and china wall. If this milling specification is calculated properly, the intake should drop into place and everything fits and lines up. The first clue that something might be wrong is if the screws do not fit into the screw holes easily. Installing the intake gaskets loosely against the head and carefully placing the manifold on top is the usual way to verify this. For the second part of this checkout procedure, see 'Port Matching' below.
Porting Matching
Any time that you port the cylinder head or install a new, high-flow cylinder head (which has bigger intake ports), you should consider matching the ports in the intake manifold with the ports in the head. In most cases, the ports in the head are larger. Also in most cases, port matching is only done on the last inch or two of the manifold's intake runner. Caution: With some of the big-port high-flow heads now available, not all intake runners can be ported to match. For example, you can't port standard 340/360 intakes to match oval-port W2 heads. The manifold must be welded up to allow this porting to occur.
A-engine cylinder heads use a heat-crossover in the center of the intake manifold. The Magnum engine and the W2 heads do not have a heat crossover passage. On A-engines, it was common to block the heat crossover passage at the manifold face to make more power. However, driveability suffers, so if you plan on true street driving or cruising, you want to keep the heat crossover working.
Carburetors
I cover only 4-barrel carburetors for max performance. Although there are several manufacturers, Holley, Quick-Fuel, and the Carter/ Edelbrock families provide the best performance and tuning options. Chrysler/Mopar mostly used Carter production 4-barrel carburetors with a few Holleys sprinkled in over the years. A few Rochester carbs were installed on trucks in the 1980s, but they do not seem to be very popular today.
With the introduction of fuel injection across the V-8 production engines, Carter Carburetor went bankrupt. A few years later, Edelbrock bought all the tooling and rights to the AFB and AVS carburetors and they are now readily available along with all the service and tuning parts that you might need.
Automounter 1 6 5 X 45 Cartridge
Before you order a carb, determine which one is best for your engine package. Your carb size must match the amount of air that the engine can flow. If the carb is too big, the engine stumbles and floods at lower RPM. If the carb is too small, the engine does not provide enough fuel at high RPM. When selecting a carb for a street engine, bigger isn't always better so don't make the classic mistake of buying a carb that's too large for your engine package.
Carb Selection
Carburetor selection should be based mainly on the engine's cubic inches, but usage (street) and other hardware (heads and cams) can also impact the selection. The primary factor in recommending a carburetor is availability, along with service parts. One of the problems is that many of the special sizes of carburetors are no longer available.
273: The 273 uses the smallest 4-barrel carburetor possible. Because the AVS is a very good street carburetor, I recommend the 500-cfm Edelbrock AVS. 318: I wanted to recommend a 600-cfm carb for this size engine but Edelbrock doesn't make one, so I recommend the 650-cfm Edelbrock AVS. The best 4-barrel choice might be the small ThermoQuad (13⁄8-inch primaries) but they aren't readily available (perhaps from Summit).
340 and 360: I recommend the vacuum secondary 750-cfm Holley (or Quick Fuel) or the 800-cfm Edelbrock AVS. You only need about 650 to 700 cfm for the 340/360 ci, but they are not available from Holley or Quick Fuel with vacuum secondaries. Therefore, the closest vacuum secondary carb is the 750 (as with any street/strip cam or head).
If you have a cam with less valve lift than .475 inch and stock-type cast-iron heads (intake flow less than 200 cfm), you should consider the 650-cfm AVS or a 650-cfm vacuum secondary Holley/Quick Fuel. The ThermoQuad provides exceptional street performance, and you can find remanufactured units at Summit Racing.
Most current performance intake manifolds are straight and do not feature wide or spread secondaries. From 1971 on, production carburetors had very large secondaries, which required the manifolds to reflect this size change. Most Chrysler production carbs of this era were called ThermoQuads (made by Carter). The Holley version was called the SpreadBore. The GM version was called the QuadraJet (made by Rochester). These are great street carbs but are difficult to find today.
The readily available carbs today, Holley 4-barrel and the Carter/Edelbrock AFB and AVS, do not have giant secondaries. Why? Production had to meet emissions requirements in the 1970s and didn't want customers complaining that their 4-barrel ran like a 2-barrel. The small primaries in these carbs allowed them to meet emissions standards and have reasonable driveability. Hibari 1 5 9. The giant secondaries increased airflow and kept performance up. Edelbrock makes an adapter for this situation.
The other really great street package is the 6-barrel (carbs still available from Mopar and Holley). Recommended for all setups, it is the best street system until MPI (the Magnum engines). However, cost could be an issue; one intake manifold plus three carbs, linkage, and air cleaners can add up. With three carbs it is more complicated than a single 4-barrel. (All the tricks are in the tuning section in Chapter 10.)
There is no SP for the 6-barrel, so packages No. 4 and No. 5 might not be available and may need to be fabricated. 390 and 400: These big-inch engines demand a lot of airflow, so the 800-cfm Edelbrock AVS is the best 4-barrel carb; the 750-cfm vacuum secondary Holley is also a good choice. The 6-barrel is an excellent choice. If you have cams bigger than .480 valve lift and heads that flow more air than 240/250 cfm, you might look at bigger carbs such as the 900/950-cfm Quick Fuel units or the Indy Heads intake with two 4-barrel carbs.
The 900/950-cfm units bolt to the standard carb pad but are double-pumpers. You can use a double-pumper, but you typically have to use more stall speed in the converter or more gear (axle ratio) or both. 420+: These engines can use more airflow, but the 750-cfm vacuum secondary Holley and the 800-cfm AVS are the baseline units. The 6-barrel is an option. The winner might be a 4500 carb (a small one at around 1,000 cfm) on a fabricated manifold or an 8-barrel on an Indy Heads manifold.
Carb Pad Gaskets
Most of the Holley and Carter/ Edelbrock carburetor gaskets have been common so that both bolt patterns are in the gasket. I recommend using a plastic or phenolic spacer between the carburetor and the intake manifold with a gasket on each side. Edelbrock has a good selection of gaskets and spacers. Only a 1/4-inch is needed but 1/2- and 1-inch phenolic spacers are more common. Throttle Body Unlike the stock 2-barrel carburetor, the Magnum 2-barrel throttle body flows a fair amount of air, about as much as a small 4-barrel carburetor. When the Magnum MPI system was introduced, several companies offered modified throttle bodies (52 mm), but those options seem to have disappeared.
2-Barrel
All Magnum MPI systems use a 2-barrel throttle body. It has a 50-mm bore size (1.967 inches). Slightly larger throttle bodies do not seem to be commercially available. One possibility is to have your machine shop bore out the throttle body to a larger size and use larger throttle blades. Be cautious because the casting isn't that thick (around 52 mm, or 2.047 inches), but you can use 52-mm throttle blades or perhaps Edelbrock 2.00-inchers.
4-Barrel
Although there seems to be only one 2-barrel throttle body, many 4-barrel throttle bodies are made by many different manufacturers. The standard carb pad 4-barrel throttle body (1.75-inch bores) flows about 1,000 cfm. Companies such as Edelbrock, Indy Heads, and Wilson Manifolds offer aluminum 4-barrel throttle bodies in the 1,000- to 1,600-cfm area. Caution: Some of these big throttle bodies are made for the 4500 Holley carb pad (big carb pad) rather than the standard 4150 pad (square-bore pad for 1.75-throttle bores).
The smaller carb pad seems to gives airflow ratings in the 1,000- to 1,200-cfm range. The bigger numbers are based on the 4500 pad and 2-inch and-larger bore sizes (1,600 cfm and up). Markdown editor mac. For a street setup, the 1,000-cfm package is more than enough.
Fuel Pump
To convert a Magnum MPI engine to a mechanical fuel pump, swap the cam and front cover for the A-engine parts. The front cover also requires the water pump to be swapped to the A-engine version. The MPI electric fuel pump is located in the gas tank. The aftermarket has upgrades for electric fuel pumps for use with multi-point fuel injection (AEM). If you swap cams to the A-engine versions to gain the mechanical pump capability, remember that A-engine tappets do not oil the valvetrain through the pushrods. Use Jeep V-8 (360, 390, 401) tappets to resolve this.
Fuel Injection
All Magnum engines were fuel injected (MPI) and most A-engines were carbureted. Once you have fuel injection, it is not one size fits all. The ECM receives input from about seven sensors to control the fuel and ignition systems. The intake manifold, the eight injectors, and the fuel rail are only the beginning. (These details are covered in Chapter 10.)
Nitrous
Nitrous kits come in many sizes based on how much horsepower you want to add: 100-hp kits, 250-hp kits, and others. You also have many ways to inject the nitrous into the engine, such as directly into the intake runner or at the carburetor flange, by using special plates (carb spacer) between the carb and the intake manifold.
The direct injector into the runner versions require the manifold to be modified for injectors, which sounds more expensive. The carb plate versions are much easier to install because they fit between the carb and the intake, don't require any machining, and have eight fewer injectors. (See Chapter 10 for more tips.)
Magnums
All the Magnum engines (1992– 2002) use the same aluminum intake manifold, and there is no big port/ small port model. The standard manifold is large and shaped like a beer barrel. These manifolds also have a bolt-on breastplate on the bottom of the intake casting designed to keep hot oil off the runners.
The key issue with Magnum intake manifolds is that all Magnum engines were MPI fuel injected. Also, Magnum heads use vertical intake manifold attaching screws, while A-engines use attaching screws that are perpendicular to the cylinder head's intake face. Intake manifolds are not interchangeable between Magnum engines and A-engines. The A-engine manifolds could be adapted by welding, but it is expensive and new manifolds are readily available.
The stock beer-barrel Magnum intake manifold is fine for stock applications, but it should be replaced for any performance project (except NHRA Stock class racing where the stock casting is required). The Mopar Performance 2-barrel single-plane intake P5007398 is a suitable replacement. It makes more mid-range and high-end performance, allows use of factory accessories, and is the same height as the stock manifold. Use installation kit P5007638 to help make the swap more user-friendly.
The stock 2-barrel throttle body flows a lot of air because it doesn't have to meter any fuel but performance customers lean toward 4-barrels. This swap requires a 4-barrel intake manifold. Do not install a 4-barrel throttle body onto any of the 2-barrel intakes. The 4-barrel aluminum single-plane intake for the Magnum heads is P5249816 for the right-hand linkage used on trucks or P4876615 for the driver-side linkage used on passenger cars. These manifolds come with a 2/4-barrel adapter so that either the production 2-barrel throttle body or an aftermarket 4-barrel throttle body can be used. The intake runners on these two intakes are slightly larger than on the replacement 2-barrel intake discussed above and, therefore, make a small increase in power over the 2-barrel intake using the 2-barrel throttle body.
All muscle car engines used a driver-side throttle linkage. The Ram trucks that received Magnum engines use a passenger-side throttle linkage. To convert an MPI Magnum to carburetor usage, the intake manifold has to be changed along with replacing the throttle body with a carburetor. In the mid-1990s through the early 2000s this swap was popular because Mopar Performance was selling Magnum crate engines converted to carburetor usage.
To convert a stock Magnum engine, you need a 4-barrel intake manifold (P5249501, single-plane) designed for use with a carburetor. It has the Magnum's vertical attaching screws, and the 4-barrel carburetor pad that fits the dual pattern for Holley or Carter/Edelbrock. When converting to a carburetor, you must have either a mechanical fuel pump or a fuel pressure regulator in the system for the carburetor to function properly.
Aftermarket Intakes
All aftermarket intake manifolds are made of aluminum, but that is about the only feature that they share. There are dual-planes, single-planes, race single-planes, 6-barrels, 8-barrels, and even supercharged versions. There are standard, W2, and Magnum port versions. Availability is constantly changing, so double-check any part with the latest information on what is in stock, what's new, and what has dropped from sight.
Dual-Planes
Edelbrock made the original dual-plane, aluminum intake manifold for the 1968 340, called the LD-340. It's now called the Performer 340/360 (revised and updated). This is a good manifold and was the standard performance part for many years. The trick with aluminum dual-plane intakes to make more power for performance projects is to mill down the divider between the driver's and passenger's sides. This trick works with any dual-plane.
The Edelbrock Performance RPM 340/360 makes more power than the standard Performer because it has somewhat larger runners (1.01 x 2.17 versus .97 x 1.95 inches) and is taller or has a higher rise (raised by about .75 to .72 inch actually).
The RPM Air-Gap 340/360 is the next intake on the performance ladder. It has about the same height and uses similar runner size as the Performer RPM, but it has a plate cast across the bottom of the manifold that keeps the hot oil off the bottom of the intake runners. Thus, it creates an air gap between the bottom of the manifold and the bottom of the intake runners. Edelbrock makes the RPM Air-Gap Magnum, and at this time, it's the only known aftermarket dual-plane for Magnum engines. It is designed for use with carburetors.
Single-Planes
Single-plane manifolds used to be considered a race-only component; low-RPM throttle response was quite poor because engines typically load up on fuel. Improved designs have now made the notion no longer valid. Edelbrock offers the Torker II and the Victor for standard 340/360 rectangular-port heads and a Victor W2 for oval-port heads. It also offers a Super Victor, which is an air-gap design and is about 1.3 inches taller than the Victor. Indy Heads offers large-port (and tall) single-planes for standard rectangular-port heads, along with 6- and 8-barrel two-piece single-plane manifolds in several versions.
Multi-Carbs
Several manufacturers offer multi-carb intakes for Mopar big-blocks, but only Indy Heads currently offers a two-piece, aluminum single-plane intake manifold for use with the 6-barrel (three 2-barrels) and the 8-barrel (two 4-barrels).
Tunnel Ram and 4500
The typical tunnel ram intake is designed for using two 4-barrel carburetors in-line; the 4500 is the largest single carburetor offered by Holley and Quick-Fuel. The 4500 does not fit the standard Holley 4-barrel carb pad attaching pattern. These manifolds have been made as castings in the past but are probably fabricated today. Indy Heads offers a 4500 cast manifold.
Fuel Distribution
With any carburetor system, fuel distribution issues are common with the intake manifold, whether cast or fabricated. These problems can be identified by using a dynamometer. The solution is always to put dams (wooden popsicle sticks) in the floor of the plenum. It is an issue with single-plane intakes but is not an issue with dual-plane intakes. Chrysler/Mopar used to provide this information (where to put the sticks), but hasn't done so for the past few years.
Fuel distribution is the basic problem. When you run an intake and carburetor on an engine, all eight cylinders do not receive the same amount of fuel and air; some are rich and some are lean. In general, the overall fuel level is adjusted upward until some cylinders are on longer lean, but that leaves the few rich cylinders. If these cylinders can be brought down to the proper fuel/ air ratio, the engine makes more power. This is one aspect of dyno testing that can be a real bonus with any single-plane intake manifold.
Manifold Selection
Because of the many possible choices this is almost as difficult as selecting cylinder heads and camshafts. Popular manifolds are kept in circulation while unpopular manifolds are dropped from production; availability is constantly changing. The same is true for cylinder heads. In addition to all that, fabricated manifolds can be expensive.
The dual-plane is the best street manifold and the Mopar Performance dual-plane has been the best of them. The Edelbrock Performer RPM has larger runners, makes more power, and is definitely the best choice for larger displacements, such as 390 to 400 inches.
Magnum
The best MPI intake for the Magnum is the Mopar Performance design. The traditional aftermarket doesn't offer many MPI manifolds so most of these options are based on the Mopar Performance line. Also, many MP manifolds have fuel-injected bosses (not machined), which can be machined for fuel injectors. Edelbrock and Mopar both offer carburetor versions; a tie.
Single-Plane Intake for Carter AFB/ AVS and Holley 4-Barrel The single-plane is basically a race or horsepower manifold with the possible exception of 390- to 400-ci engines. The two styles of standard 4-barrel carburetors (the Holley and the Carter) work well on the single-plane. The Mopar single-plane is overall best, but the race version is best for ported-head engines and larger displacements. If this manifold isn't available, the Edelbrock Super Victor (air gap) is best.
6-Barrel: Only the standard manifold is available from Mopar. For larger displacements and/or ported-head engines, the Indy Heads two-piece would be interesting. 8-Barrel: Today's choices are limited, but the Indy Heads 2 x 4–barrel intake looks interesting for larger displacement engines.
Manifold Prep
Chapters 1 and 5 discuss various milling ratios: deck, intake face, and china wall. If this milling specification is calculated properly, the intake should drop into place and everything fits and lines up. The first clue that something might be wrong is if the screws do not fit into the screw holes easily. Installing the intake gaskets loosely against the head and carefully placing the manifold on top is the usual way to verify this. For the second part of this checkout procedure, see 'Port Matching' below.
Porting Matching
Any time that you port the cylinder head or install a new, high-flow cylinder head (which has bigger intake ports), you should consider matching the ports in the intake manifold with the ports in the head. In most cases, the ports in the head are larger. Also in most cases, port matching is only done on the last inch or two of the manifold's intake runner. Caution: With some of the big-port high-flow heads now available, not all intake runners can be ported to match. For example, you can't port standard 340/360 intakes to match oval-port W2 heads. The manifold must be welded up to allow this porting to occur.
A-engine cylinder heads use a heat-crossover in the center of the intake manifold. The Magnum engine and the W2 heads do not have a heat crossover passage. On A-engines, it was common to block the heat crossover passage at the manifold face to make more power. However, driveability suffers, so if you plan on true street driving or cruising, you want to keep the heat crossover working.
Carburetors
I cover only 4-barrel carburetors for max performance. Although there are several manufacturers, Holley, Quick-Fuel, and the Carter/ Edelbrock families provide the best performance and tuning options. Chrysler/Mopar mostly used Carter production 4-barrel carburetors with a few Holleys sprinkled in over the years. A few Rochester carbs were installed on trucks in the 1980s, but they do not seem to be very popular today.
With the introduction of fuel injection across the V-8 production engines, Carter Carburetor went bankrupt. A few years later, Edelbrock bought all the tooling and rights to the AFB and AVS carburetors and they are now readily available along with all the service and tuning parts that you might need.
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Before you order a carb, determine which one is best for your engine package. Your carb size must match the amount of air that the engine can flow. If the carb is too big, the engine stumbles and floods at lower RPM. If the carb is too small, the engine does not provide enough fuel at high RPM. When selecting a carb for a street engine, bigger isn't always better so don't make the classic mistake of buying a carb that's too large for your engine package.
Carb Selection
Carburetor selection should be based mainly on the engine's cubic inches, but usage (street) and other hardware (heads and cams) can also impact the selection. The primary factor in recommending a carburetor is availability, along with service parts. One of the problems is that many of the special sizes of carburetors are no longer available.
273: The 273 uses the smallest 4-barrel carburetor possible. Because the AVS is a very good street carburetor, I recommend the 500-cfm Edelbrock AVS. 318: I wanted to recommend a 600-cfm carb for this size engine but Edelbrock doesn't make one, so I recommend the 650-cfm Edelbrock AVS. The best 4-barrel choice might be the small ThermoQuad (13⁄8-inch primaries) but they aren't readily available (perhaps from Summit).
340 and 360: I recommend the vacuum secondary 750-cfm Holley (or Quick Fuel) or the 800-cfm Edelbrock AVS. You only need about 650 to 700 cfm for the 340/360 ci, but they are not available from Holley or Quick Fuel with vacuum secondaries. Therefore, the closest vacuum secondary carb is the 750 (as with any street/strip cam or head).
If you have a cam with less valve lift than .475 inch and stock-type cast-iron heads (intake flow less than 200 cfm), you should consider the 650-cfm AVS or a 650-cfm vacuum secondary Holley/Quick Fuel. The ThermoQuad provides exceptional street performance, and you can find remanufactured units at Summit Racing.
Most current performance intake manifolds are straight and do not feature wide or spread secondaries. From 1971 on, production carburetors had very large secondaries, which required the manifolds to reflect this size change. Most Chrysler production carbs of this era were called ThermoQuads (made by Carter). The Holley version was called the SpreadBore. The GM version was called the QuadraJet (made by Rochester). These are great street carbs but are difficult to find today.
The readily available carbs today, Holley 4-barrel and the Carter/Edelbrock AFB and AVS, do not have giant secondaries. Why? Production had to meet emissions requirements in the 1970s and didn't want customers complaining that their 4-barrel ran like a 2-barrel. The small primaries in these carbs allowed them to meet emissions standards and have reasonable driveability. Hibari 1 5 9. The giant secondaries increased airflow and kept performance up. Edelbrock makes an adapter for this situation.
The other really great street package is the 6-barrel (carbs still available from Mopar and Holley). Recommended for all setups, it is the best street system until MPI (the Magnum engines). However, cost could be an issue; one intake manifold plus three carbs, linkage, and air cleaners can add up. With three carbs it is more complicated than a single 4-barrel. (All the tricks are in the tuning section in Chapter 10.)
There is no SP for the 6-barrel, so packages No. 4 and No. 5 might not be available and may need to be fabricated. 390 and 400: These big-inch engines demand a lot of airflow, so the 800-cfm Edelbrock AVS is the best 4-barrel carb; the 750-cfm vacuum secondary Holley is also a good choice. The 6-barrel is an excellent choice. If you have cams bigger than .480 valve lift and heads that flow more air than 240/250 cfm, you might look at bigger carbs such as the 900/950-cfm Quick Fuel units or the Indy Heads intake with two 4-barrel carbs.
The 900/950-cfm units bolt to the standard carb pad but are double-pumpers. You can use a double-pumper, but you typically have to use more stall speed in the converter or more gear (axle ratio) or both. 420+: These engines can use more airflow, but the 750-cfm vacuum secondary Holley and the 800-cfm AVS are the baseline units. The 6-barrel is an option. The winner might be a 4500 carb (a small one at around 1,000 cfm) on a fabricated manifold or an 8-barrel on an Indy Heads manifold.
Carb Pad Gaskets
Most of the Holley and Carter/ Edelbrock carburetor gaskets have been common so that both bolt patterns are in the gasket. I recommend using a plastic or phenolic spacer between the carburetor and the intake manifold with a gasket on each side. Edelbrock has a good selection of gaskets and spacers. Only a 1/4-inch is needed but 1/2- and 1-inch phenolic spacers are more common. Throttle Body Unlike the stock 2-barrel carburetor, the Magnum 2-barrel throttle body flows a fair amount of air, about as much as a small 4-barrel carburetor. When the Magnum MPI system was introduced, several companies offered modified throttle bodies (52 mm), but those options seem to have disappeared.
2-Barrel
All Magnum MPI systems use a 2-barrel throttle body. It has a 50-mm bore size (1.967 inches). Slightly larger throttle bodies do not seem to be commercially available. One possibility is to have your machine shop bore out the throttle body to a larger size and use larger throttle blades. Be cautious because the casting isn't that thick (around 52 mm, or 2.047 inches), but you can use 52-mm throttle blades or perhaps Edelbrock 2.00-inchers.
4-Barrel
Although there seems to be only one 2-barrel throttle body, many 4-barrel throttle bodies are made by many different manufacturers. The standard carb pad 4-barrel throttle body (1.75-inch bores) flows about 1,000 cfm. Companies such as Edelbrock, Indy Heads, and Wilson Manifolds offer aluminum 4-barrel throttle bodies in the 1,000- to 1,600-cfm area. Caution: Some of these big throttle bodies are made for the 4500 Holley carb pad (big carb pad) rather than the standard 4150 pad (square-bore pad for 1.75-throttle bores).
The smaller carb pad seems to gives airflow ratings in the 1,000- to 1,200-cfm range. The bigger numbers are based on the 4500 pad and 2-inch and-larger bore sizes (1,600 cfm and up). Markdown editor mac. For a street setup, the 1,000-cfm package is more than enough.
Fuel Pump
To convert a Magnum MPI engine to a mechanical fuel pump, swap the cam and front cover for the A-engine parts. The front cover also requires the water pump to be swapped to the A-engine version. The MPI electric fuel pump is located in the gas tank. The aftermarket has upgrades for electric fuel pumps for use with multi-point fuel injection (AEM). If you swap cams to the A-engine versions to gain the mechanical pump capability, remember that A-engine tappets do not oil the valvetrain through the pushrods. Use Jeep V-8 (360, 390, 401) tappets to resolve this.
Fuel Injection
All Magnum engines were fuel injected (MPI) and most A-engines were carbureted. Once you have fuel injection, it is not one size fits all. The ECM receives input from about seven sensors to control the fuel and ignition systems. The intake manifold, the eight injectors, and the fuel rail are only the beginning. (These details are covered in Chapter 10.)
Nitrous
Nitrous kits come in many sizes based on how much horsepower you want to add: 100-hp kits, 250-hp kits, and others. You also have many ways to inject the nitrous into the engine, such as directly into the intake runner or at the carburetor flange, by using special plates (carb spacer) between the carb and the intake manifold.
The direct injector into the runner versions require the manifold to be modified for injectors, which sounds more expensive. The carb plate versions are much easier to install because they fit between the carb and the intake, don't require any machining, and have eight fewer injectors. (See Chapter 10 for more tips.)
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Superchargers and Turbos
During the past few years all three major American auto manufacturers have introduced supercharged engines. Whether this OEM development is the cause or not, there seems to be a lot of aftermarket interest with superchargers and supercharging kits popping up on many projects. Indy Heads offers supercharger manifolds and many superchargers are available.
Supercharger manufacturers offer kits with all the necessary parts. Bbedit powerful text and html editor 13 0 5. Turbo manufacturers, which include Precision Turbo, Garrett, Turbonetics, and BorgWarner, make all the parts but don't put them together in kits. On the other side, there are many turbocharger manufacturers but not many kit manufacturers. (More tips in Chapter 10.)
Final Installation and Prep
Intake manifolds are pretty much 'buy it and bolt it on.' The key item to check is the manifold fit/alignment and the port alignment. The last thing to check on the manifold is how the throttle bores line up over the carburetor pad. It's generally not an issue with dual-plane intakes or with Magnum engines, but you need to check single-plane 4-barrels and the end carbs on a 6-barrel.
Written by Larry Shepard and Posted with Permission of CarTechBooks
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