Factory exhaust systems were designed to fit within the space constraints of a particular chassis while maintaining a specific noise limit at a reasonable cost. While that might not detract from the performance of a typical passenger car application, additional performance at every speed can be attained by replacing the factory components with high-performance aftermarket pieces, including tubular exhaust headers, larger-diameter piping, and free-flowing mufflers. And that tends to increase noise.
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To attain maximum possible performance from any engine, a vehicle’s exhaust system should provide the least amount of restriction. It should include tubular headers, large-diameter exhaust tubing, free-flow mufflers, and usually some type of crossover pipe. A properly installed system should tuck up tightly against the floorpan to provide the greatest amount of ground clearance.
A cast-iron exhaust manifold that simply collects exhaust gas and routes it to the head pipe was used on most standard performance Pontiac engines. These log type manifolds, as they’re often referred to, offer no exhaust tuning or pulse scavenging to improve performance. Only available in a D-port configuration, I don’t recommend them for any application beyond a stock rebuild.
Pontiac developed a “tuned” header constructed of cast-iron for its early Super Duty engines and it was an excellent piece. It performed as well as any tubular header of the era. Its only drawback was weight. A cast-aluminum version was produced for weight-conscious racers. RARE manufacturers cast-iron and aluminum reproductions.
An abbreviated version of the cast Super Duty header was developed for Pontiac’s high-performance street applications. The “long branch” manifold fits many full-size Pontiac models from the 1960s including the Grand Prix, as well as first-generation Firebirds. RARE offers excellent reproductions with 2.5-inch collectors. A Super Long Branch version is available with a 3-inch collector.
A low-restriction, dual-exhaust system to allow greatest possible performance was made available in 1956 and commonly used through 1974, at which point a single exhaust catalyst was added, ending the possibility of using true dual exhausts.
High-Performance Exhaust Manifolds
As engine displacement increased throughout the 1950s and 1960s, Pontiac began experimenting with high-flow exhaust manifolds that featured long, individual runners that merged into a large collector area to improve horsepower, particularly at high RPM. Basically a cast header constructed of iron, it featured a bolt-on collector that had a separate flange that could be uncapped to bypass the remaining exhaust system to achieve maximum performance in competition settings. Available through dealership parts departments, Pontiac’s high-flow cast headers became part of its factory-installed Super Duty package introduced in 1962.
The cast-iron headers were very heavy. A cast-aluminum version was developed to reduce overall vehicle weight for those regularly competing in drag races. The cast-aluminum header was significantly lighter and performed suitably, but aluminum alloy technology and the casting and heat-treating processes were in their infancy. Durability issues were common in vehicles that were operated for extended periods. Claims that molten aluminum would literally drip from the exhaust system may be a bit exaggerated, but I have seen the dividing wall between the center ports eroded away.
Exposure to a countless number of heating and cooling cycles throughout an engine’s lifetime makes original cast-iron exhaust manifolds prone to cracking. Unless required for a numbers-matching application, I don’t recommend using original high-performance manifolds in any build. Excellent reproductions are available.
A streamlined exhaust manifold was developed for the 1967 400 H.O. available in the GTO that model year. It was used with many other Ram Air engines over the years, as well as the 1973–1974 Super Duty 455 (shown). The “Ram Air” manifolds, as they’re often called, resemble “shorty” headers and fit tightly against the block for maximum clearance. They’re a popular choice for many A-Body applications as well as second-generation Firebirds.
At least two companies offer near-exact reproductions of Pontiac’s most famous exhaust manifolds. They continue to be a popular choice for many high-performance builds where a stock appearance is desired. They are available from most restoration parts supply houses specializing in Pontiacs for a reasonable cost. Ceramic coating (top) adds extra cost.
A slimmer version of Pontiac cast header was developed for high performance street applications during the early 1960s. These “long-branch” manifolds, as they’re commonly called, feature long individual runners like the original cast header, but its collector was an integral part of the casting, which was flanged to mate to exhaust piping. The design was compatible with all full size Pontiacs produced during the 1960s and the new Firebird introduced in 1967.
The long-branch manifold wasn’t compatible with the intermediate A-Body platform, so Pontiac developed a streamlined exhaust manifold that debuted in 1967 on the 400 H.O. It became synonymous with Pontiac’s A-Body-spec Ram Air engines beginning in 1968, and many commonly refer to it as an H.O. or Ram Air manifold. It was used through 1972 in certain A- and G-Body applications and many 1970–1974 Firebird models as well.
The factory high-performance exhaust manifolds are an excellent choice for Pontiacs that are primarily street driven. Along with quiet, leak-free operation, you’re likely to find at least one type that fits your particular chassis. The original castings are quite old, however, and it’s sometimes difficult to find crack-free examples. While original castings can sometimes be purchased reasonably, reproductions are available.
Reproduction Factory Manifolds
A few companies reproduce Pontiac’s most popular high-performance exhaust manifolds. In my opinion, those from Ram Air Restoration Enterprises (RARE) are the best.
With the exception of the cast Super Duty header, Pontiac’s high-performance exhaust manifolds were originally available in D-port (top) and round-port (bottom) configurations for use with corresponding cylinder heads. Modern reproductions are available in both styles and they are not interchangeable. If you plan to use reproduction manifolds with aftermarket cylinder heads, be sure verify with the manufacturer which configuration is correct.
RARE offers its reproduction Ram Air exhaust manifolds with a larger-than stock outlet size to improve airflow. It’s a very popular option that adds several horsepower to most engines and is recommended if you plan to use original style manifolds in your build. Be sure that the head pipes are appropriately sized for the manifold outlets.
RARE offers exact reproductions of Pontiac’s cast header originally used in early Super Duty applications in iron or aluminum. It also offers near-exact castiron reproductions of Pontiac’s longbranch and Ram Air manifolds with D-port and round-port configurations. RARE also offers a Super Long Branch manifold which features a 3-inch collector for easy connection to a high-performance exhaust system. Its Ram Air manifold is available with an oversized collector area measuring nearly 2.5 inches for added performance. RARE’s cast-iron manifold generally sells for $400 to $600 depending upon the casting. I highly recommend them any time original high-performance exhaust manifolds are considered.
Tubular Headers
Exhaust headers produced from round exhaust tubing offers the least amount of exhaust restriction, providing the greatest potential for power output.
Primary tube and collector diameters can affect horsepower and torque. Larger-diameter tubes can improve airflow at very high RPM, but it can sacrifice charge velocity, which can negatively affect torque output, particularly at low speed. The best header for a large-cube Pontiac that’s primarily street driven typically contains a primary tube diameter between 1.75 and 2 inches, and a collector diameter of 3 inches.
Gasket leaks are quite common with headers. A thick cylinder-head flange is ideal because it’s very rigid and doesn’t distort when tightened. That allows an even gasket seal, which can otherwise blow out when exposed to large volume of high-pressure exhaust, particularly when considering the varying rates of thermal expansion as the components reach normal operation temperature. Cometic produces an excellent multilayer steel exhaust gasket that’s intended to prevent leaks in performance engine.
Depending upon the chassis, some headers do not allow sufficient room for the stock oil filter housing and/or stock-size filter. It’s very close on this example, and accessing the filter with the engine installed may be challenging. A small-diameter filter is one option, while a remotely located filter may be a better choice if space constraints do not allow the stock setup.
There’s little need for a complete exhaust system on a dedicated race car. Instead, the header tubes dump out into normal atmosphere to provide the least amount of exhaust restriction. Such headers are typically custom made to fit the exact application, and some snaking may be required to fit the particular chassis.
The size of your engine, cylinder head airflow, and the RPM range you plan to operate it in will dictate which size is best for you. There are a number of companies producing high-quality Pontiac headers today, including Doug’s, Hedman, Hooker, and Mad Dog. Headers from such companies generally sell for $400 or more, but fit well, have a thick cylinder head flange to protect against gasket leaks, and include a flanged collector to accommodate the installation of a complete exhaust system. Your Pontiac vendor can suggest a set that’s best for your Pontiac model and particular engine application.
There are a few different header types available, including shorty, three-tube, four-tube, and tri-y. Each has a specific purpose and price point.
Shorty Style
Shorty headers fit and perform similarly to Pontiac’s Ram Air exhaust manifold. Hedman offers a D-port version in its Hedder line for GTO and Firebird models that features 1.625–inch-diameter tubing that steps to 1.75 inches to improve low-RPM torque, and 2.5- and 3- inch collectors. Selling for about $300 per set with a black paint finish, they’re very well made and are an excellent alternative to Ram Air manifolds when attempting to save weight. Hedman offers a high temperature ceramic coating that adds about $200 to the cost.
Hedman produces a shorty-style header for GTO and Firebird applications. On a dyno it performs similarly to a RARE Ram Air manifold with oversized outlet, but it weights substantially less. That benefits weight-conscious racers that are working with limited chassis space. Like other Hedman products, its shorty header is well made and has a very thick cylinder head flange to prevent gasket leaks.
Three-Tube Style
Three-tube headers look similar to full-length four-tube headers. These contain separate end tubes, but the center tube is large enough to collect exhaust from both exhaust ports at the center of a Pontiac cylinder head. The center tube sacrifices performance, but it’s easier and cheaper to produce, giving hobbyists an affordable tubular header that’s usually easier to install because its three tubes take up less space.
Several companies offer three-tube headers. While they may be adequate for a low-performance rebuild, I don’t recommend them for high-performance use.
Four-Tube Style
The best-quality headers have four primary tubes, one for each exhaust port on a particular cylinder head. In a four-tube design, the primary tubes snake through the chassis and merge into a single collector, and it generally promotes greatest peak horsepower. Depending upon the header manufacturer, primary tube diameter can measure from 1.625 inches to as much as 2.125 inches, and collector diameter can range from 3 to 3.5 inches.
Four-tube headers offer the greatest performance potential as they offer the least amount of restriction to exhaust flow. They are, however, rather large and can be difficult to squeeze into a tight chassis. Installation may require raising one side of the engine and/or inserting them from below. I recommend purchasing headers from a popular manufacturer. The quality and consistency is generally very good.
Doug’s Headers is a very popular manufacturer. It offers full-length four-tube headers for many popular Pontiac applications. They’re among the best fitting units available today and can be purchased reasonably from your favorite Pontiac vendor or large mail-order supplier.
Four-tube headers consume much under hood space. That places the tubes very close to important accessories such as the starter. The heat source causes a large, stock starter to overheat and fail, and the tube routing makes it impossible to remove or replace without disconnecting the header from the engine and/or raising the engine to gain clearance. An aftermarket high-torque starter like that from IMI is a compact design that dissipates heat much quicker than the stock unit. I recommend such a unit anytime full-length four-tube headers are used.
Tri-Y Style
A tri-y header has four primary tubes, which are gathered into pairs. The pairs then merge into a collector, which leads into a secondary tube, and the two secondary tubes then merge into one large collector. The design acts much like traditional four-tube headers at high RPM, but it improves cylinder scavenging, which tends to improve mid-range power numbers. They are an excellent compromise that works very well on high-performance street engines.
H-O Racing developed an excellent tri-y header that fits many popular Pontiac models. Available with D-port and round-port exhaust configurations, it was quite popular during the 1970s, 1980s, and 1990s. It has since been discontinued, but used sets in excellent condition occasionally appear on Pontiac-specific classified lists or internet auction sites.
Ceramic Coating
Ceramic coating exhaust manifolds and tubular headers is a popular process. In addition to leaving behind a durable, high-quality finish that doesn’t discolor when exposed to exhaust heat, it creates a thermal barrier that limits dissipation of exhaust charge heat through the pipe as the charge makes its way toward the muffler and tailpipe. That allows the charge to maintain a greater degree of velocity and that can improve performance slightly. It also limits the amount of heat that radiates from the manifold or header, reducing underhood temperature.
Ceramic coating not only provides an attractive finish that’s very durable, it also acts as a thermal barrier that prevents exhaust heat from dissipating too quickly, slowing the charge as it exits. In addition to silver ceramic coating for tube headers, natural cast-iron (gray) is a popular color for cast exhaust manifolds.
Many companies offer high-quality ceramic coating. Expect to spend more than $200 for coated cast-iron exhaust manifolds and even more for full-length tube headers. If you do not find someone to do this locally, some shops provide mail-order service. I am familiar with Trail Performance Coating in Omaha, Nebraska, and can recommend its services. The quality of its work is excellent and pricing is quite affordable.
X- and H-Type Crossovers
The addition of an exhaust crossover in a dual-exhaust system can improve the scavenging that occurs as exiting exhaust pulsations draw the exhaust charge from adjacent cylinders. The scavenging lessens the amount of work each piston must do when forcing the exhaust gas from the cylinder and into the exhaust manifold or header. That can yield a definite performance improvement. There are two types of crossovers commonly found on performance vehicles: H and X. Determining which your Pontiac performs best with, if any at all, may require some trial and error.
An X-type crossover creates a split junction that merges the head pipes, allowing the exhaust pulses from one to draw off the other, improving exhaust scavenging, and engine performance. It also gives the exhaust charge two paths in which to exit, effectively increasing the capacity of the entire exhaust system.
A large-cube engine moves a significant volume of air, and the diameter of the exhaust tubing must be great enough to support it. It’s not uncommon to find a system with tubing 3 inches or more, which is required to maintain peak performance. Round tubing is popular but significantly reduces ground clearance on low-slung models.
An H-pipe is a balance tube that connects two head pipes. It can be constructed of a length of tube that’s the same diameter as the head pipes or slightly smaller. It allows a certain degree of scavenging, but its greatest benefit is balancing the pressure pulsations within each head pipe. That can smoothen the sound emitted at the tailpipes, and can improve performance slightly.
An X-pipe merges the two head pipes at a junction. It improves exhaust scavenging but also gives the exhaust charge two paths in which to exit. I have found that an X-pipe offers at least some advantage in most engines. I’ve seen a slight improvement of midrange torque and peak horsepower on my own Pontiacs with an X-type crossover when compared to not having one. The X-pipe also produces a smoother, higher pitched exhaust note that sounds finely tuned.
Mufflers
Factory muffler were designed to attenuate a specific exhaust tone and maintain a manageable noise level in and out of the car. Most high performance muffler are designed to produce a more aggressive sound while maximizing exhaust system flow. The aftermarket muffler from Dynomax, Flowmaster, Magnaflow, Pypes, and Spintech are among the most popular with Pontiac hobbyists.
Many muffler manufacturers have sound clips on their websites. I suggest visiting those sites or attending local shows or cruises to determine the sound you’re looking for.
Complete Exhaust Systems
Several muffler companies offer a complete exhaust system for many popular Pontiac models. It generally includes high-flow muffler and large-diameter exhaust tubing that’s aluminum coated or constructed of stainless steel and prebent for the application. Along with the muffler manufacturing companies mentioned above, Ram Air Restorations Enterprises (RARE) also offers complete Pontiac exhaust systems.
Round exhaust tubing measuring 3 inches or more may be impractical for some applications. RARE offers a complete exhaust system that features oval tubing entering the muffler and round tailpipes to maximize available space. The oval tubing provides the same amount of total area as a round pipe, but it doesn’t sacrifice valuable ground clearance.
When considering a complete exhaust system for your Pontiac I recommend one with the largest-diameter tubing. A diameter of at least 2.5 inches is mandatory, but I suggest 3-inch tubing if possible. It gives the exhaust charge a greater area to expand and dissipate its heat before it reaches the mufflers. Even larger tubing is available, but its overall diameter can present clearance issues, particularly with a low-slung chassis.
Some companies produce oval tubing that provides the required area without the clearance issues. Tailpipe diameter isn’t as critical since the charge has lost most of its heat and velocity by the time it exits the mufflers.
Written by Rocky Rotella and Posted with Permission of CarTechBooks
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