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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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.
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.
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.
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.
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 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.
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.
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.
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 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.
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 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.
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.
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