Manifolding

Words: Larry Shepard

In past articles I have discussed the engine’s block, heads, rotating parts, intake manifold and valvetrain, and looking at these individual engine parts can be misleading. The intake manifold must work with the induction system selected and it must work with the cylinder heads. However, there are tuning issues that should also be considered. The intake and exhaust manifolding have a great affect upon the engine’s tuning and therefore the engine’s performance output, horsepower and torque. Back-pressure in the exhaust and inlet restrictions also affect the overall performance numbers and also need to be considered. Remember that the engine is actually a big air pump and how-the-air-flows-in and how-the-air-flows-out may be just as important as 
the hardware inside. All parts need to work together as a team.

You would like to check every part and its various affects on engine performance. This test procedure would require a tremendous amount of time on a dyno and cost way too much, so I feel this approach is unrealistic for general street-strip projects. The key is to try to tune your package for maximum results for your desired applications. Once an engine is built, engine builders don’t usually like to take it apart so tuning is generally done with the intake system and exhaust system. If we include the camshaft in our tuning package, the number of possibilities is almost overwhelming. Therefore, I will try to limit the scope of the discussion and try to keep it in general terms.

Let’s start with the intake side. The key part is the intake manifold itself. The intake port runners must match the cylinder head. For example, the standard 440 head uses a standard size runner like the 4 bbl intake P4529463 while the Max Wedge big-block heads use a much larger runner like the 8 bbl, cross-ram P5007330. The cross-sectional shape of the runner is also important like the oval-port W2, P5249572AB (4 bbl, dual-plane) versus the smaller, rectangular ports used in the standard 340/360 heads. The intake manifold also defines the configuration of induction system like the 8 bbl, in-line 426 HEMI® P5153737 (AFB carbs) or the 8 bbl cross-ram 426 HEMI, P5007534. You could select a 6-bbl-style intake like the 440, P4529056. The general design of the intake manifolds tends to be divided into two groups: dual-plane and single-plane. The typical single-plane 
4 bbl like P4876334 (small block A-engine) tends to turn a higher rpm than the dual-plane 4 bbl like P4876335AB. This makes dual-planes street manifolds, while single-planes are race manifolds. While you can port intake manifolds similar to cylinder heads, this grinding operation is generally limited to port-matching on intakes. For serious racing, you can change the manifolds runner length a small amount but the biggest gains come from switching designs like the 5.2L and 5.9L Magnum® production barrel-style intake to a HP single-plane. Most fuel injection systems use an injector location near the manifold parting-line so the intake holds the key to an EFI system like SP manifold, P5007790, which can use either a 2 bbl or 4 bbl throttle body.

The air gets to the carburetor or throttle body through the air cleaner. The air cleaner tends to be a big part of the inlet restrictions. The air cleaner base is directly related to the carburetor set up so you have a standard 4 bbl version like P4529002 (chrome) and the 6 bbl style, P4529057AB (non-cold-air), or the 8 bbl inline version, 77R06313 (426 HEMI AFBs). Most of these large diameter, high-performance air filters 
are pretty efficient. They were designed for high-performance production packages in the 1960s and ‘70s. Interestingly on the mid-1990s and newer production cars, the hood lines are low, the engine compartment very crowded, and the resulting air cleaners are very compromised. As a result, the high-performance aftermarket developed cold-air induction systems for these newer vehicles that typically moved the air cleaner element forward into the radiator-yoke area so it can pickup cold air that flows below the bumper and below the radiator. The re-located air cleaner is typically connected to the throttle body with a high-flow, smooth, pre-formed plastic tube. These cold-air systems can result in excellent performance gains – like 77060003AC (2005–10 Charger/300/Magnum/Challenger w/5.7L HEMI). There are similar units for 2000–05 Neon 2.0L SOHC (77060022AB) and 2004–06 Wrangler 4.0L in-line 6 (77060007AB). There are many other versions. These HP induction systems are also available from aftermarket manufacturers. To date, the aftermarket has not designed these new-style induction systems for the older (1960s, ‘70s or ‘80s) cars/engines. So to use this type of induction system on an older vehicle, you would have to adapt one of the newer engine kits to your vehicle.

You might not consider the air cleaner as part of the engine tuning package because it isn’t part of the intake runner length and the cylinder head intake port length, but it generally increases the engine output so it is somewhat like free performance.

In the old days (before the early 2000s), to build a nice street/restoration car you started with two basic bodies: one is the actual project car and the second is considered the parts car. With the advent 
of new sheet-metal from Mopar®, these left-over parts cars can be turned into nice project cars. Perhaps the most popular engine to power this increase in car-projects is a crate motor. Since it comes fully assembled, there are limits on the tuning adjustments that you might make. While you might swap the engine’s intake manifold (single-plane for dual-plane perhaps or a 4 bbl for a 6 bbl), you have more tuning options in the exhaust side.

While the exhaust begins with the port in the cylinder head, I’ll start with the exhaust manifold. The production exhaust manifolds are made of cast iron. The base-engine parts (2 bbl or standard 4 bbl) are called log manifolds. The performance engines like the Road Runner 383 (1968–69) and the 440 HP (called an A134) used high-flow cast manifolds. There are several versions that can be identified by the 7-digit part number cast into the part. If you don’t have a set of these ’68–‘69 manifolds, they are available new from Year One, Yearone.com. Year One also offers the ’66–’71 426 Street HEMI cast iron exhaust manifolds. The ’62–’63 Max Wedge, very smooth and high-flowing exhaust manifolds (nicknamed French horns) are also available from the aftermarket.

The next tuning tip is exhaust headers and there are many kinds of headers. Typical V-8s use a 4-into-1 design like P5155282AB (2005–08 Charger/300/Magnum w/5.7L HEMI). The street and race headers have the typical street header design using slightly smaller tube sizes while the race header, commonly called competition, uses larger tube sizes and equal lengths plus adjustability in some models. There are shorty-headers which were originally developed for street rods but can be handy in any limited-space project. Perhaps the most unique header is the one for the V-10 Viper, P5155828 (2010 models), because it has five runners going into the collector.

To get the exhaust gases from the exhaust manifold or header to the rear of the car, you will need some exhaust pipes. Typical high-performance V-8s use dual exhaust – one exhaust pipe on each side. For performance purposes (tuning and noise) you want to use an H-pipe which connects the two sides and typically crosses over under the transmission cross-member. On newer cars (probably newer than 1985), the next part is the catalytic converter. On earlier HP cars from the 1960s and 70s, the muffler (one per side in most cases) was the only other part in the exhaust system rearward of the exhaust manifold/header. On the newer cars, it is mounted rearward of the catalytic converter. Low-restriction, high-flow mufflers are common today.

The term “Cat-backTM” exhaust came about in the 1990s because it is legal to replace the production exhaust system rearward of the catalytic converters which almost all cars had by 1990. This means that the muffler and tailpipes can be upgraded for improved performance. Cat-back systems are very popular and have become very hi-tech. They are also very popular and there are many manufacturers. The cat-back exhaust for the V-10 Viper, P4510608 (2003–06 SRT10®), is a side-exit version. The cat-back exhaust for the 2009–10 Challenger 5.7L HEMI (auto trans.), P5155754, has dual exits. There are many other versions for newer Jeep® vehicles, trucks and many passenger cars. Exhaust pipes, mufflers and tailpipes for A-, B- and E-Body performance cars (mid-1960s through the mid-‘70s) aren’t technically cat-back exhaust but there are some nice systems based on this technology. There are companies that offer 2", 2 ½" and 3" full exhaust systems for the popular engines and body styles. The standard exhaust systems tended to be 1 ¾" to 2" and the high-performance versions were around 2" to 2 ¼" so these new, hi-tech systems can flow a lot more and offer greatly reduced back-pressure.

The rear-most part of the production exhaust system is the exhaust tip. There were many versions and styles used on the various models like 77R06139 used on the ’70–’74 ‘Cuda (2.5"). There are many more and most are available from Mopar—new.

As you can infer from the above discussion on intake and exhaust manifolding, there are many, many options. To make a successful project/engine, you want all your parts to work together—intake and exhaust manifolds, heads, cams, displacement etc. With so many choices, you should try to select your parts based on an overall package approach. Many years ago, these packages or teams were called Bracket Tips. Today the latest versions of these parts packages are listed on various HP books on the 426 HEMI (HP 1525), the 6 BBLs (HP 1528), Magnum V-8 (HP 1473) and Small Block V-8 (HP 1405) which are available at many book stores and at many speed shops.

Mopar offers several more manifolds, exhaust systems, cat-back exhausts, headers and cold-air intakes. For additional information, 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).

Larry “Shep” Shepard is a retired Mopar Performance engineer, author of numerous Mopar Performance books and a Michigan Motor Sports Hall of Fame inductee.