Let It Breathe

Words: Larry Shepard

In the last few articles of Tech Insider, we have covered crate engines, engine blocks and cylinder heads, so we can now move on to intake manifolds. In many cases, the cylinder block dictates aspects of the cylinder heads and intakes and features of cylinder heads and ports affects the intake manifolds. Once you define the block, heads and intake manifold, you have pretty much defined a crate motor. Or you can use this information to make your own crate motor with any number of variations.

The intake manifold sits on top of the engine and therefore is more visible than the block or heads once the engine is assembled. It is a part that can be prettied-up (polished or custom-painted) to improve the overall appearance of the engine compartment. For this article, I’m only going to discuss the intake manifold, but heads and blocks have to be included along with carburetor or throttle body basics. Actually, the cylinder head’s air flow and the cfm (cubic feet per minute) capability of the carb/throttle body should both be used when selecting an intake manifold. Another aspect to be considered is the fuel delivery system, which actually delivers fuel to the carburetor, but the carb and intake manifold must work very closely together.

One of the newest intake manifolds, the Street HEMI® 8-bbl in-line P5153737, is actually a resto/replacement for the original 1966–71 426 Street HEMI. It is cast aluminum and looks just like the original. It hasn’t been available new for over 30 years. It is designed for two AFB carburetors or Edelbrock Performer versions and also accepts AVS or Edelbrock Thunder series carburetors. All production carbs on this manifold were AFBs that flowed around 600 cfm. There are 700 and 800 cfm versions of the AVS (Thunder Series) that would make a very nice up-grade for this manifold package and general street use. This approach is not legal for NHRA/IHRA class competition (Stock and Super Stock).

There is another 8-bbl intake manifold for the 426 HEMI engines that is considered the Holley version, P4510633. It is made of cast aluminum and uses the carbs in-line. On this manifold the carb flanges are machined to accept two Holley carbs. The Holley carb has the float bowl on the front and rear of the carb and this makes Holley carbs longer so the in-line configuration requires the carb-pads to be further apart. This manifold was originally called the marine manifold.

Since almost all 426 HEMI engines built in production used the dual-carb arrangement and single 4-bbl carbs are generally the most popular setups, the single 4-bbl 426 HEMI intake manifold is the dual-plane, P4876188. It might make a very nice street package to have this manifold machined to accept an AVS carb and use the biggest AVS carb with this manifold on the street. More on the racing side, and large displacements, the single-plane 426 HEMI is P5153781. It is machined for the standard Holley carb and has large runners for use with big ports, and large cubic inches. It is shipped directly from the supplier so allow a couple days for shipping.

The newest 426 HEMI intake manifold is the 6-bbl, P5153738. It is a dual-plane so it is designed for dual-purpose use or street use. It uses the same hardware as the 440 engine. The carbs have the same spacing so even the air cleaner can be the same. For displacements in the 426 to 452 area, the general 440 fuel curve tips should yield the proper air/fuel ratio. On the other end of the scale is the big, 8-bbl cross-ram, P5007534, which is actually three pieces. The lids to the plenums are removable so you can tweak the runners and plenum features. An actual restoration HEMI cross-ram (either magnesium or aluminum) is available from A&A Automotive and Transmission Repair (317-831-5610, www.aandatrans.com).

The newest engine family, the Gen III HEMI (5.7L, 6.1L), is produced with multi-point fuel injection. The single-plane MPI replacement manifold for the 5.7L is P4510582. The single 4-bbl carburetor version for the 5.7L is P4510581. The 8-bbl carbureted in-line manifold for the 5.7L HEMI engine is P5153556. The single-plane intake for the 6.1L for use with a 4-bbl throttle body (MPI) is P5155288. This is also the manifold that is being used on the 5.7L and 6.1L HEMI Challenger Drag Pak vehicle. The reason the 5.7L and 6.1L production engines use different intake manifolds is the different production heads but the same heads are used on both 5.7L and 6.1L HEMIs in the Drag Pak vehicles.

The big blocks are called B or RB engines and use production sizes of 383/400(B) and 440(RB). They illustrate one of the reasons blocks have to be considered during intake manifold selection. The 440 6-bbl intake manifold is P4529056 while the 383 version is P4529055. So if you plan on building a large displacement engine based on the 383 (or 400) short-deck block, then you have to use the 383-style manifolds. However, there is a trick. The aluminum Stage VI heads P4529335 have raised ports and if they are used on the short-deck B-blocks (383 or 400), then you can use the wider, 440-style intake manifolds. A standard width manifold, Max Wedge port, single-plane intake is P4876337. The wider, Max Wedge port single-plane intake for use with the raised-port Stage VI heads is P4876128. The new, hi-rise dual-plane single 4-bbl intake for the RB or 440 engines is P5153525. The biggest big-block intake manifold is the 8-bbl cross-ram P5007330. It is designed for use with Max Wedge, big-port heads on a 440 block. It should be used with installation kit P5153338 to help with the swap. There are no short-deck 383/400 block cross-rams. Tip: try the Stage VI head approach if you want to use any of these 440-unique manifolds on a short- deck 383/400 block. However, A&A Automotive and Transmission Repair (317-831-5610, www.aandatrans.com) makes a resto-version of the 1962–64 Max Wedge cross-ram. Additionally, they can change the casting slightly with smaller 440-style ports because you can’t seal big Max Wedge intake ports to standard 440 heads.

Tip: Most of the later production 440-6-bbl and 426 HEMI engine packages used a vapor separator 77R06295 mounted after the mechanical fuel pump and below the alternator/water pump. While these special fuel filters are almost mandatory on all of these engines, they can be added to others like 318s and 340/360s. They are great for summer cruising. Note: if you don’t have one, they require a small fuel return to the gas tank. On street cars, these filters should be replaced regularly.

There are lots of intake manifolds for use on the Mopar small blocks. The standard dual-plane intake is P4876335AB and the single-plane is P4876334. The standard dual-plane W2 intake is P5249572 (9.56" deck height). The standard deck, W2 single-plane intake is P4529408AB (water-heated). One of the trick combinations is the W9 heads like P5007065AB and the 9.56" deck height intake P4876162 because the W9 head flows so much air without requiring cnc-porting. Talk to an engine builder or the Mopar Direct Connection Techline 1-888-528-HEMI (4364) for further details relating to valve train and cam tappet angles.

The Magnum® or 5.2L and 5.9L engines were built from 1992 and newer and are a close relative of the A-engine or small block Mopar but use the vertical intake manifold attaching screws (defined by the cylinder heads) and this aspect makes the Magnum family of intake manifolds unique from the other small block Mopars. All of the production Magnum engines were built with multi-point fuel injection and a large, round intake manifold often called a beer-barrel, based on its shape. A single-plane MPI intake manifold for these engines is P5007398AB with EGR or P5007852 w/o EGR. These two intakes should use installation kit P5007638 to help with the swap. The single 4-bbl carbureted dual-plane intake for the Magnum heads is P5007381AB while the single-plane version is P5007380AB. The HP 4-bbl single-plane version (P5007790) is listed as a 2/4-bbl version because it comes with an adapter to cover more applications. This manifold used in its 4-bbl configuration is being used on the 5.9L Wedge versions of the Challenger Drag Pak vehicle.

For a complete listing of Mopar intake manifolds and other performance parts visit www.mopar.com and click on the 2009 Mopar Performance Parts Catalog link.