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Basic Elements of Exhaust Systems
Replacing your vintage vehicle exhaust system
When your vintage vehicle needs a new exhaust system or components, you are faced with a wide variety of options and decisions about the parts you will install. Here are some of the critical things you need to know and consider before spending your hard-earned dollars on that next exhaust system.
We are focused here on typical Four-stroke Internal Combustion (IC) engine systems for vehicles built from the earliest days of the horseless carriage up to the introduction of catalyzed systems in the mid-1970s. Newer vehicles utilize the same basic components, but also employ catalytic converters (2 or 3-way), a variety of thermal and oxygen sensing components and active control technologies to meet emissions standards.
Let's start with the basic elements of exhaust systems. Most single systems consist of an exhaust manifold, exhaust pipe, silencer (muffler and/or resonator) and tailpipe. Dual systems typically use two exhaust pipes or an H pipe, two to six mufflers/resonators and two tailpipes. We'll start with a brief review of your material choices and then cover each of the major components in turn.
Material Choices
When you replace exhaust components, you can choose from a variety of materials. The OEM parts installed on your new vehicle were typically manufactured in low-carbon steel. Beginning in the late 1930's, mufflers were often made using galvanized steel for improved corrosion resistance. Aluminized steel and stainless steel were introduced into mainstream production vehicle exhaust components in the late 1970's. Most OEM manufacturers introduced stainless steel components after 1975 with the advent of catalytic converters.
Today, you will find components manufactured from these materials:
- Low-carbon steel (poor corrosion resistance, but "correct" and original for most vehicles). Most "Old Stock" parts are low-carbon, "regular" steel or galvanized parts.
- Aluminized steel (very good corrosion resistance and durability; performs and looks good for many years with typical vintage vehicle usage and care)
- Stainless steel (excellent appearance and durability. "300" Series stainless is more brittle and has poorer thermal shock performance than "409" Series stainless, which is most often used in today's OEM stainless systems.
Cast iron exhaust manifolds or tubular exhaust headers
Typical original equipment (OEM) production manifolds are manufactured from cast iron (inexpensive, durable and tolerant of high-temperature gases). These manifolds are "optimized" to balance production costs, manufacturing simplicity, ease of assembly, durability and performance. They direct the hot exhaust gases away from the cylinder head/exhaust port and into the primary exhaust pipe. They are not generally capable of optimal flow, but they are quiet, durable and strong. In many cases, they incorporate a heat riser valve or pre-heater to aid in cold engine warm-up, emissions control and drivability.
Many high-performance applications in the 1960's and 1970's utilized long-tube manifold designs to improve output and engine breathing. The Pontiac HO/Ram Air manifolds, the MOPAR Max Wedge, Hi-Po & Hemi manifolds and the Ford Hi-Po manifolds are all examples of these higher-flow manifolds. These designs improved exhaust gas flow over standard manifolds by utilizing a design that more closely resembles a tuned-length header. Though not as free-flowing or effective at scavenging exhaust gas as tuned headers, these manifolds represented a superior alternative to the basic "log" that most production manifolds resemble.
Performance part suppliers jumped into the performance improvement aftermarket with tubular headers for nearly every engine and vehicle combination. By matching the length of the header tubes, the exhaust pulses from each cylinder can be tuned to reach the exhaust pipes in an orderly fashion. Well-designed manifolds or headers can actually improve the scavenging of spent exhaust gases from the cylinders by using the pulse from previous cylinder output to "pull" the gases from the next cylinder – almost as if the exhaust pulse is being vacuumed out of the cylinder by the previous pulse. A good set of headers can improve torque and horsepower by more than 10% compared to standard factory exhaust manifolds.
If you are using production, cast iron manifolds in your vehicle, follow these steps to help ensure a quiet, trouble-free installation. Make sure that the sealing surfaces are flat and that the heat riser valve (if originally present) is properly installed and operating freely. Treat the manifolds with a high-quality cast iron coating after media blasting them. Use bolt locks where they were originally installed and a high-quality gasket. Follow the bolt installation sequence that is specified in your service manual and tighten the attachments to the specified torque in the proper sequence. (Usually starting at the center and working alternately forward and rearward) This maintains the flat sealing interface between the manifold and the head and minimizes the potential for leaks and cracks.
H pipes, X pipes and competing claims
There are many suppliers of performance exhaust systems making claims of huge torque and horsepower gains to be had by utilizing their X or H pipe designs. Do your homework; evaluate the claims in light of your intended use of the vehicle and be certain that the claims are substantiated by hard data, preferably comparisons of vehicle performance with ONLY that specific exhaust system change having been made between comparative measurements. Dynamometer data is useful, but be certain that you understand what was done to the engine/vehicle to achieve the published results. Most of us won't be operating our vintage vehicle for extended periods under racing conditions, so consider how important the results are for your vehicle driving patterns!
There ARE inherent benefits to improving the breath-ability of your exhaust system. Engines are basically big air pumps. The less restriction there is to exhaust flow, the better the engine can process incoming fuel/air mixtures and the more power the engine will produce. H Pipes provide a balance of the exhaust gas pulses between the two exhaust pipes, equalizing the system pressure in the two "sides" of the exhaust system. This generally provides improved low-end torque and some amount of top-end horsepower improvement. An "X" pipe design may provide a slightly better result than a simple H pipe on identical applications, especially at higher engine speeds. Whichever way you go, be certain to re-tune your engine for the changes you've made in the exhaust system. A reduction in exhaust system back pressure can allow improved breathing, which will probably require carburetor re-jetting, idle mixture and idle speed adjustments, ignition timing adjustment and spark plug changes.
Many high-performance vehicles manufactured after 1960 were available with factory-installed duals that incorporated H pipes. In many cases, your car can be equipped with an OEM style H pipe and duals, even if it was originally equipped with a single exhaust system. The factory dual system can be a great performance and sound improvement.