The application of engine and engine internals determine the exhaust system requirements. Street, street/strip, road racing, drag racing, or any other particular application places the engine under different operating conditions. A street engine typically does not rev high, and strong torque is often the goal. On the other end of the spectrum, road racing engines rev high for nearly an entire race, so the engine and exhaust must produce the best performance at the upper end of the rev range. And, therefore, they require a much different exhaust system to run at their best.
This Tech Tip is From the Full Book, HOW TO BUILD SUPERCHARGED & TURBOCHARGED SMALL-BLOCK FORDS. For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://mopardiy.com/building-mopar-engines-for-performance-exhaust-system/
In essence, an exhaust system must be tailored to a particular engine component package and use. In other words, when it comes to headers and exhaust, one type, design, or size does not fit all.
The exhaust system must physically fit in the particular vehicle, and because of that, tube length, size, and routing is constrained by the chassis. The manifold bolts to the head and lines up with the ports in the head and the head’s attaching bolt pattern. However, much of the rest of the exhaust system (length, diameter, shape, and bend) can affect the engine’s performance and its torque and horsepower curves. Because it affects the engine’s performance, the complete system should be considered rather than only the manifold bolt pattern.
Most of us look at the header or exhaust manifold as a part that must fit the engine compartment. We often don’t tend to give much thought to the rest of the exhaust system other than its basic fit to the body and its connection to the manifold.
Because the exhaust manifold or header bolts to the engine, you could consider it an accessory, but the exhaust system affects the engine’s torque and power curves. This means that you need to select the proper hardware to work best with the rest of your engine package and for your application.
The only performance choice used to be a single exhaust or a dual exhaust, and the dual exhaust tended to come with big engines, with no real option for smaller engines. Early big-block exhaust development for the 1967 440 HP package (GTX and R/T models) led to the high-flow 340 exhaust manifold in 1968. The 340 manifolds were the standard for small-blocks for many years after 1968. From an engine performance standpoint, the 1968 340 exhaust manifolds are a giant gain over the 273/318 log manifolds, and they fit in the engine compartment, plus they are quiet and durable.
For years, headers and exhaust systems were made of mild steel. Then some aftermarket manufacturers began offering stainless steel versions. Stainless offers durability advantages over mild steel. Typically stainless steel alloys contain at least 12-percent chromium and also have a very low percentage (less than .2 percent) of carbon. Some versions have high nickel content, which are popular in race cars and offer welding advantages. Low-nickel alloys are used in OEM production exhausts.
Performance exhaust manifolds for small-blocks started with the 1968 340 engine package. These cast-iron exhaust manifolds are very good for performance. Because they were a compact design, they fit more body styles, but the less-swoopy design doesn’t flow as much air. The 1970 and newer versions are not quite as good.
This remained the basic situation until the introduction of the 5.2L Magnum engines in 1992. The two sets of cast-iron manifolds provide about equal performance on the dyno. The 340 driver-side manifold is slightly better than the Magnum; the passenger-side Magnum manifold is slightly better than the 340. The 340 driver-side manifold is the most impressive looking in the engine compartment.
The A-engine and the Magnum engine share the same exhaust manifold bolt pattern. The W2 performance cylinder head used a wider-spaced bolt pattern when it was originally introduced. When the head was reintroduced in the late 1980s, the new W2 was machined with both bolt patterns. W2 heads used headers.
Air enters the engine through the intake manifold and then flows through the cylinder head and engine. This airflow must be matched on the exhaust side to allow the increased airflow to exit the engine. This technology was originally used by Magnum engines from 1996 through 2003, but the aftermarket has advanced since then. The science isn’t as important as availability. Street headers use small tube diameters and street/strip systems use slightly larger tubes. The big tubes are generally used on highly modified race engines only.
The four common tube sizes are 11⁄2, 15⁄8, 13⁄4, and 17⁄8 inches. A 2-inch header tube is considered a race item. Street headers usually have either 11⁄2 or 15⁄8 tubes. Street/strip headers usually use 13⁄4-inch tubes. The 400-inch engines usually use 13⁄4 tubes for the street and 17⁄8-inchers for the street/strip. TTi step headers are good for both applications.
The typical shorty header or block-hugger header tends to be in the middle; it is an upgrade on the stock cast-iron manifold but not as good as an actual header.
A number of factors need to be considered when selecting a header for your particular engine package and application. Do not fall into the trap of thinking bigger is better. Instead, you need to embrace the idea of the correct-size header for the engine combination, so the trick is determining the best size and dimensions.
If you install a large 2-inch header on a mild or moderate street engine, your engine has little torque. In such cases, the owner often blames the poor design of the header, but that’s not true. Most of the time, a 11⁄2- to 15⁄8-inch pipe is an appropriate size for an engine that revs between 1,500 and 6,000 rpm.
Street versions have a small primary diameter (around 15⁄8 inches) and are somewhat easier to install. A mid-level primary diameter on the collector is about 21⁄4 or 21⁄2 inches. The racing versions usually have larger primary diameters (around 13⁄4 to 17⁄8 inches) and a larger collector (21⁄2 to 3 inches).
Equal-length primary tubes, desired in a race header, are very difficult to fit into a “street” engine compartment. The first cylinder’s tube tends to be too long and the last tube tends to be too short. In some cases the solution to these problems was to run some tubes out through the fenderwell and back under the frame to gain the length. Fenderwell headers are generally the last choice because you have to cut up your car. The A-engine in the early A-Body (1966 and earlier models) is one package that fits into this last category.
Hedman, Hooker, and TTi offer headers for pre-2004 small-blocks; other manufacturers focus on newer cars built in the past 10 years of production. The street header with 11⁄2- or 15⁄8-inch tube diameter is the most popular. The larger 13⁄4- and 17⁄8-inch (Hooker) are more difficult to find, but Hedman may make headers that are not shown in the catalog, such as a 13⁄4-inch four-into-one header. The TTi 15⁄8 and 13⁄4 step header may work well in several packages.
Tri-Y headers commonly offer more torque and often provide a better fit in the engine compartment. The shorty header or block hugger was originally designed for street rods, but its use has spread to many other types of vehicles because it fits the engine compartments so much better than other styles of headers. The step header is the latest design and was developed for racing and is a special version of the four-into-one, where the four primaries have two different diameters as they go from the head to the collector.
All of these headers have dimensions such as tube diameters and primary lengths and these sizes and lengths are developed for a specific engine on the engine dyno. Tri-Y headers have been around forever, but they are difficult to find, and currently Doug Thorley shows a 15⁄8 Tri-Y header (for trucks). Most super Stock engines (drag racing) use a custom-made version of the Tri-Y header.
Performance gains for headers and low-restriction exhaust systems vary because the stock systems range from log manifolds and single exhaust pipe, to 340 manifolds and dual exhaust. Generally 5 to 10 percent is a good baseline gain. As the engine becomes larger, a good exhaust system becomes more important. One caution: On the Magnum engines, because they are computer controlled, performance additions such as headers and a cat-back exhaust put the engine on the edge of being too lean. Another change from the stock system could cause an engine failure. When computer-controlled engines become too lean, they lose performance rather than gain it. At that point, you must have the ECM reprogrammed or a new computer installed.
The primary tube length of the header needs to be sized for the application and engine package. Some have heaped praise on equal-length headers, but once they are hooked up to a conventional exhaust system with mufflers, the performance gain is negated.
Shorty and mid-length headers have been proven to produce nearly as much horsepower as long-tube headers and are suitable for a street car. Shorty headers provide a performance improvement over OEM cast-iron manifolds, and for some cars and trucks, shorty headers are the only option, so then it’s simply a matter of determining the correct tube diameter.
As the most common headers, four primary tubes, varying in length from 24 to 36 inches, carry the exhaust gases from each cylinder to the collector.
The Tri-Y style of headers was one of the first designs. A Tri-Y header design starts at the head with four tubes matched to the four exhaust ports. After the four tubes come out of the flange, they are joined (merged) into two tubes. Then these two tubes are joined into one at the collector.
Originally the Tri-Y was noted for torque, while the four-into-one header was noted for horsepower. So over time, the Tri-Y header fell into obscurity. In the mid-1990s, SEMA asked the California Air Resources Board (CARB) to create a test program for performance parts so they could be sold for street use. Each part is tested and, if approved, assigned an emission exemption number.
Header manufacturers jumped at the chance to have street-legal exhaust products. They looked at various designs on the dyno, focusing on street vehicles and street use. They found that the Tri-Y design offered more torque and they could match or improve on the power of the four-into-one designs. The lengths of the primary and secondary tubes were different from the original designs and the tube sizes were changed, but the end result was that these Tri-Y headers made more torque and more power.
Shorty Headers The shorty header is technically a four-into-one design, but instead of having 30-inch-length primaries, it has 6-inch primaries. It was originally made for street rods because enthusiasts tend to install big V-8 engines into small engine compartments that were designed for 4s and 6s. The shorty’s biggest advantages related to ease of installation and fit into the engine compartment.
Technically step headers are another version of the four-into-one header. With a typical race header with all primaries designed at the same length, the tube size is constant. The primaries become larger and the length changes tuning for different performance characteristics, but the tube diameter stays the same for a given design.
With a step header, the primary tube changes size after 6 to 12 inches and may change size again before it reaches the collector. That diameter size change is called a step. These steps and the length of tube in each step are determined by extensive testing on an engine dynamometer. Each set of sizes and lengths is unique to the specific engine and RPM package.
The purpose of all this testing is to gain the best of both worlds: best torque while maintaining the best power. The typical step header is a race item that is custom-made based on lengthy dyno development. However, TTi offers an off-the-shelf step header that work well with all engine packages.
The flange of a header bolts to the cylinder head and looks somewhat like a thick steel exhaust gasket. Each primary tube is welded into the flange. The exhaust openings in the flange are cut out. These ports in the flange come in several shapes, such as round, square, and D-shaped, plus others. Most small-blocks use the square shape except for the W2 heads, which use a D-shaped flange opening.
The typical exhaust header collector is a straight/round 21⁄2- to 3-inch-diameter tube; the merge collector is tapered inside and out. Where the four tubes come together, the center point is extended and tapered to a point. The outer wall of the collector tapers slightly over a short distance. Then the collector expands until slightly larger than a standard collector. The length of the taper is changed for different tuning effects. Generally the high-flow and high-velocity exhaust gases in the merge collector try to increase the amount of torque and broaden the torque curve.
For 1980 and newer engines, the cast-iron manifolds use at least one oxygen sensor. They are also installed in the exhaust system ahead of the catalytic converter(s). Although not required on most A-engines, all Magnum engines have these sensors. If the exhaust manifolds are replaced with headers, the oxygen sensor should be reinstalled. This allows the ECM to function properly. The ECM controls both the amount of fuel and the amount of spark that the engine receives.
The engine’s oil filter is attached to the passenger’s side of the engine toward the rear. Header tubes generally work toward the rear of the engine compartment as they begin to exit the engine compartment. One of the primary tubes of the headers often tries to hit the oil filter. The easy solution is to move the oil filter with the right-angle adapter (available from Mopar Performance, among others).
Headers come with a variety of coatings, and these are applied mainly for appearance. Some are used as a form of heat shield or thermal barrier. Although some companies specialize in various coatings, most exhaust coatings are offered by the header or exhaust manufacturer. Coatings can be ceramic, polished ceramic, and nickel-chrome plated.
Manufacturers also offer thermal barriers that are applied inside the tubes. Although each type of coating offers unique features, the main focus of the heat barrier is to keep the exhaust gas heat inside the tube and not allow it to heat up the engine compartment.
The H-pipe is a short tube that connects the driver-side and passenger-side exhaust pipes on any dual exhaust. The 340 and the bigger 360 engines can benefit from the H-pipe. Originally it was placed where you wanted the collector to end. So if the dyno testing showed that an 18-inch collector was the best package, you placed the H-pipe or crossover pipe at the end of the 18-inch collector.
Keep in mind that the floorpan design and transmission may not provide adequate clearance, so you have to verify that it fits the car. In most cases, the H-pipe crosses under the transmission crossmember or just to the rear of it, which puts it under the transmission output shaft/ housing. Manufacturers today produce H-pipe, maybe 3 feet long, with the crossover pipe welded together. These could be added to almost any exhaust system.
Similar to the H-pipe, the X-pipe connects the driver-side and passenger-side exhaust pipes to share the exhaust pulses. X-pipes are also made in about 3- to 4-foot sections, all welded together, and can be installed in almost any exhaust system. In general, manufacturers produce X-pipe kits in 21⁄2- and 3-inch pipe sizes so that it can match up to the exhaust system. This is a little tricky.
In general, manufacturers produce X-pipe kits in 21⁄2- and 3-inch pipe sizes so that it can match up to the exhaust system. This is a little tricky. Flowmaster says there is no horsepower gain with either X or H crossover pipes. TTi says they provide a gain of more than 10 hp on a 400-hp engine package. Both crossovers are readily available from Flowmaster and TTi so I use one or the other; the crossover has always been good for performance. This hardware needs more investigation.
Mufflers and Catalytic Converters
At the beginning of performance small-block production, glass-packs and dual-exhaust conversions were common. As headers became popular, customers looked for better (lower restriction) mufflers. Early answers were the Street Hemi muffler (1966– 1971) and the Imperial muffler. The Imperial was very good for performance, but it was larger than the Street Hemi and was difficult to fit into the smaller vehicles that carried the small-block. Another answer was the turbo Corvair, or the turbo muffler. It was smaller and easier to fit under cars.
Muffler manufacturers, such as Flowmaster, Borla, Magnaflow, TTi, and Dynomax, make suitable products for max-performance small-blocks. TTi and Dynomax Super Turbo mufflers are very compact and should fit most applications. The other three companies offer muffler bodies that are about 14 inches long and 18 to 19 inches long. But these may not fit all areas of the chassis.
Flowmaster and Dynomax offer a variety of inlet and outlet sizes; most are 2.5 or 3 inches. These mufflers can be positioned in the center, on the driver’s side, or on the passenger’s side, depending on length considerations. Predicting sound level and tune is almost impossible, but that is one feature that manufacturers work hard to do. Back pressure is the key to performance. Short mufflers are probably the best option, but you should discuss the sound issue with the manufacturer or the local outlet or your local muffler shop.
Exhaust manufacturers are working on the exhaust tuning science on 2004 and newer vehicles and engines. On these vehicles, the catalytic converters are left on the vehicle and technicians tune what is ahead of them (headers) and what is behind them (mufflers and exhaust pipes). These mufflers are state-of-the-art hardware and the muffler may fit your application, but there is no install hardware so it must be a custom install at your local muffler shop.
Many racetracks began requiring race cars to have mufflers in both drag racing and circle track racing. This restriction tended to be a local, rather than national, development. In the 1960s, manufacturers started looking for and developing low-restriction, lightweight, small, and easy-to-install mufflers. This led to better mufflers that actually lowered the engine’s back pressure and still kept the noise at reasonable levels.
Today, these small mufflers are offered on a wide range of configurations with overall lengths of 13 to 20 inches. In most cases, the underside of the car dictates the specific style: center entrance, driver-side exit, or almost any other combination. These performance mufflers come in 2.25-, 2.5-, and 3-inch tube sizes to fit just about any exhaust system.
The “cat-back system” is a term that came about in the late 1990s to refer to exhaust systems that moved components behind the production catalytic converter. This typically means that the muffler and tailpipes are revised.
As the emissions testing era began in about 1995, the main enforcement agency (CARB) determined that the exhaust system behind the catalytic converter was free (open) and could be replaced. This made the term “cat-back exhaust” a performance standard.
Many manufacturers started making cat-back exhausts. Because the A-engine didn’t have many catalytic converters in production, manufacturers didn’t make these systems for the 1960s, 1970s, and 1980s cars. However, the technology works on new and old cars. Basically, on vehicles built after 1995, a cat-back system reduces the overall exhaust system’s backpressure by 50 percent. Potentially this change can result in gains of 5 to 7 percent in power.
Aftermarket tailpipes come in lengths of 2.25, 2.5, and 3.0 inches. I use the 2.25 version with up to 300-hp engine packages, the 2.5 version for up to 400 hp, and the 3.0 version for more than 400 hp. Caution: On new cars or trucks with MPI, a true dual exhaust (two pipes from the exhaust manifolds to the rear of the vehicle) should not be used unless you plan on reprogramming the ECM. Typically on these newer vehicles, the large drop in back pressure can confuse the sensors that input to the ECM and engine performance may suffer.
Sealing the exhaust manifold to the cylinder head can be a challenge. Cast-iron manifolds are easy, even with a thin gasket. Headers can be a problem. The header flange is not as stiff as the cast-iron exhaust manifold. In some cases, the header manufacturer designs in a small ridge around the port opening to help the gasket seal to the cylinder head. Using thicker gaskets (1/16 inch) also helps.
Today, some exhaust gaskets are made of a high-temperature material that is stronger and more resistant to leaks. A good tip is to apply some high-temperature silicone to both sides of the gasket before installation.
Written by Larry Shepard and Posted with Permission of CarTechBooks
GET A DEAL ON THIS BOOK!
If you liked this article you will LOVE the full book. Click the button below and we will send you an exclusive deal on this book.