Gen III/IV engines have the same basic requirements for their exhaust system as other automotive engines, but these high-performance engines have specific EFI system requirements that must be met for the system to perform properly. The LS engine requires at least one oxygen sensor (as many as four), which must be placed a minimum of 18 inches from the engine, but also needs to be close enough to stay hot, which is within about 4 feet. Other issues include transmission crossmember clearance, header fitment, and exit placement.
All EFI systems require oxygen sensors to read the oxygen levels in the exhaust. These vital sensors tell the computer if the engine is running rich, lean, or just right. But that is not all: All LS engines come with catalytic converters, which are used to burn up the exhaust gases to reduce emissions. This is a very important factor to consider that requires a bit of homework.
This Tech Tip is from the full book, SWAP LS ENGINES INTO CHEVELLES & GM A-BODIES: 1964-1972. For a comprehensive guide on this entire subject you can visit this link:
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Most states have a classic car provision that exempts older vehicles from emission standards and/or safety inspections, but it is imperative that you research the current laws in your state before completing your swap. Some states require the vehicle emissions to match the standards for the year of the engine, not the vehicle, which requires the engine to retain all original smog equipment (including the exhaust gas recirculation [EGR] valve, air injection reaction [AIR], and catalytic converters) in working order. Every state is different, and the laws are constantly being revised and changed, so it is up to you to make sure your LS swap is legal in your state.
Stock Gen III/IV exhaust manifolds are efficient and can help make more than 400 hp for most engines. The trick is finding a pair that fits your body; the motor mounts and engine installation typically determine exhaust manifold compatibility. One set of manifolds may fit one install and not fit another. Test fitting is the only way to verify fit.
Each starter is also clockable, so it can be rotated to clear obstacles, which makes it perfect for any LS swap.
Stock exhaust manifolds also need a compatible flange that can be welded to the rest of the exhaust system. Several flanges are used on stock exhaust manifolds, but not all of them are reproduced. The trick here is to make sure you include some of the stock exhaust, the section just below the flange, so that you have the right flanges for the exhaust manifolds. If the flange is not available, fabrication is the only option.
Speedway Motors reproduces exhaust flanges for the LS1 and Vortec manifolds. Another source for flanges is used catalytic converters. You can’t buy a used converter, but you can buy the flanges. Most salvage yards will gladly cut them off and sell them to you.
Using the exhaust gasket as a pattern, you can cut a flange using a plasma cutter. An acetylene torch certainly cuts the steel, but it’s not the correct tool for this job because it also warps it to the point that it isn’t usable for an exhaust flange. Depending on your install, there are a couple of ways to cut new flanges.
The most common material for flanges is mild steel. For a good seal, material of 1/8 inch or thicker should be used. With a good basic outer dimension measured from the manifold or exhaust gasket, your local metal supply shop should be able to provide a plate cut to fit. Depending on the shop, they may be able to cut
out the entire part for you. Otherwise, using the basic plates, you can trace the inside of the gasket to the plate and then, using a plasma cutter, trim out the plate to the outside edge of the line. Any metal overhang can cause some turbulence in the airflow, which impedes flow and reduces horsepower but does not significantly affect performance if the overhang is small.
If you do not have access to a plasma cutter, the following procedure allows you to remove any metal overhang. Using a drill bit, drill to the line at some point. If you are using Z06 manifolds, do this in each corner. Then place the flange in a vice and use a reciprocating saw, air body saw, or hacksaw to cut out the center section. It may take a while, but it works. A plasma cutter, of course, certainly makes the quickest work of the job.
An aluminum flange looks great with stainless, chrome, or polished exhausts. Cutting aluminum is easier than cutting steel and a good-looking set of aluminum flanges could be cut from plate aluminum with a band saw and a scroll saw quite easily. Aluminum is softer than steel, so the aluminum flanges must be thicker than their steel counterparts. Aluminum flanges should be made from at least 1/4- or 3/8-inch plate. The cutting process is the same. Plasma torches quickly cut aluminum, so be careful. If you use the hand-cut method, aluminum is softer, making it a little easier. Also, aluminum cleans up nicely with carbide tips and a die grinder.
If your local shop is equipped with a CNC plasma or water jet, you can pay them to cut the parts for you. The cutting part is usually not very expensive, but the program writing time is typically around $50 per hour. Because the flanges are simple, it shouldn’t take a shop longer than an hour. Once the program has been written, a shop can make as many as you want. If you are doing multiple swaps, you can amortize the cost to several engines.
Bridging the gap between a factory manifold fitment and the performance of headers are Hooker cast-iron LS manifolds. These manifolds provide tight fitment coupled with better flow performance and they use 2010 Camaro–type flanges. The manifolds come with the flanges and use the OEM gaskets for a leak-free seal.
2014–Up Gen V LT-Series Manifolds
Currently, the factory offers two types of manifolds for the LT series:
Corvette and truck. The Vette manifolds do not fit the A-Body at all, not even close. The truck manifolds have been reported to fit in some applications, but I have not been able to verify that. Although the flanges are very similar to the LS’s, the bolts are in different places, so swapping LS manifolds to the LT is not feasible.
With all the challenges of modifying stock manifolds, most swappers prefer aftermarket headers designed for engine swaps. Ground clearance is a common concern. Mid-length headers tend to fit best and offer the most ground clearance, but long-tubes certainly work for LS swaps as well. Manufacturers such as Hooker, Edelbrock, and Dynatech custom-fit headers for the most popular LS swap vehicles.
Choosing headers requires careful measurements and research. You need to be careful: Some headers might fit your application but have the stock-style flange, putting you back in the same boat. Sure, you could chop off the stock flange and weld on a new one, but isn’t that part of the reason you are buying aftermarket headers? Some vehicle-specific headers fit late-model chassis and are designed for LS engines. These headers do not have the stock-style flange, making them excellent candidates for swap applications.
Vehicle-specific swap headers come with the universal three-bolt triangular flange that has been used for decades. This ensures that the headers easily mate to the rest of the exhaust. Kits are available for specific vehicles that include the headers and exhaust, all in one package.
This conversion kit includes Edelbrock headers made of 409 stainless steel tubing with 3/8-inch-thick port and collector flanges. The collectors use graphite donut gaskets instead of the leak-prone three-bolt collector and gasket. These fit 1964–1972 GM A-Body cars including the Chevelle, Malibu, El Camino, Cutlass, 442, Skylark, Buick Special, GS350, GS455, GTO, LeMans, and Tempest. The Gen III/IV swap headers have 13⁄4-inch primary tubes stepped up to 17⁄8 inches for maximum flow and power.
Edelbrock recommends using the Edelbrock LS-series engine mount kit (PN 6701) with the Edelbrock swap headers.
For those with Edelbrock E-Tec– series LS heads or Vortec Fast Burn heads, the Edelbrock swap headers (PN 65083) have the correct port flange configuration, so they are compatible with stock A-Body engine mounts.
The Edelbrock LS swap exhaust system matches with the headers and engine mounts, though the system works well with other mounts and headers. The exhaust system is constructed from 21⁄2-inch 409 stainless-steel tubing with an X-pipe assembly and includes a pair of SDT mufflers and a pair of polished stainless-steel tips. This kit fits the same vehicles as the headers.
Hooker builds a couple of vehicle-specific LS swap headers: first-generation Camaro and Firebird and GM A-Body, in addition to its universal block hugger LS headers.
The 1966–1972 GM A-Body: These headers are built with lightweight, 18-gauge tuned-length 13⁄4-inch primaries, with 3-inch smooth-transition slip-fit-style collectors. This yields a leak-free fit to the rest of the exhaust. The headers are designed to fit tight to the chassis, giving increased ground clearance, from 1 to 3 inches, which is especially helpful for lowered vehicles.
This Tech Tip is from the full book, SWAP LS ENGINES INTO CHEVELLES & GM A-BODIES: 1964-1972. For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this post on Facebook / Twitter / Google+ or any automotive Forums or blogs you read. You can use the social sharing buttons to the left, or copy and paste the website link: https://www.lsenginediy.com/how-to-choose-the-right-exhaust-for-your-ls-swapped-chevelle/
The cylinder head flanges are made from 5/16-inch machined steel for a good seal. To accommodate the oxygen sensors, the headers include 3- to 21⁄2-inch slip-fit reducers with oxygen sensor bungs welded in, plus a set of extra bungs for a 3-inch exhaust system.
Hooker LS swap headers fit most manual and automatic GM transmissions, including the Tremec 5- and 6-speed manual transmissions. These headers fit other vehicles as well; research is required. These headers are designed to work with the Hooker LS swap adapters and crossmembers.
Hooker Block Hugger: This LS swap header design is tuned for low- and mid-range street performance from idle to 3,500 rpm. The primaries are made from 18-gauge 15⁄8-inch mild steel tubing, which is mandrel-bent and tuned by length to reduce backpressure and increase exhaust velocity. This design delivers more power and torque with crisp throttle response; the 21⁄2-inch collectors with a 3/8-inch-thick three-bolt flange make installation simple.
The head flange is machined to ensure a flat surface for a tight seal. The tight-tuck tube design is used to fit within narrow street rod frames and provides a good fit in most vehicles that do not have a dedicated swap header. The collectors exit parallel with the oil pan for maximum ground clearance in lowered vehicles and are positioned to clear the starter and engine mounts.
Specifically for A-Body cars, these full-length headers feature 17⁄8-inch primaries with a 3-inch collector made from 16-gauge steel and a V-band type of flange for easy leak-free maintenance. They are available in ceramic-coated or natural finish.
2014–up Gen V LT Headers
At press time, no A-Body-specific headers are available for the LT. For the GS shown in this book, I had a set custom-made using the LS tube pattern for the A-Body with LT flanges. It is very close, but needs a little tweaking before it is perfect. With that in mind, by the time this book is on the shelf, there should be several LT-compatible options for A-Body swaps. The biggest difference is that the heads are slightly different, so the angle of the flanges must change. I have not tried any headers for trucks or Corvette applications; some mid-length or shorty-type headers may fit the A-Body.
Your swap project must be equipped with a catalytic converter if the area or state where you license the vehicle mandates and tests vehicles for carbon emissions. You want to choose a catalytic converter that enhances performance yet meets emissions standards. Research on the construction of a catalytic converter will inform your decision.
The most important part is the ceramic matrix. Shaped like a honeycomb, the matrix is made predominantly of a ceramic material called cordierite. The honeycomb is created through an extrusion process in which lengths of the honeycomb shape are squeezed through a die and supported by computer-controlled jets of air that keep the honeycomb straight as it leaves the machine.
Once the ceramic honeycomb is fired and set, it receives a washcoat of various oxides combined with the precious metals that function as the actual catalyst. The washcoat is used because it evenly disperses the metals throughout all the pores of the matrix. The metals are generally mixed to best use their individual properties. Most cats in the United States use some combination of platinum, palladium, and rhodium. Outside the United States, copper has been tried, but it forms dioxin, a toxic substance with carcinogenic properties. In some places, materials such as nickel, cerium in washcoat, and manganese in cordierite are used, but each has its disadvantages.
Originally developed throughout the 1930s and 1940s for industrial smoke stacks, catalytic converters began to be developed for automobiles in the 1950s by inventor Eugene Houdry. The first cats were mandated in 1975. They were of a two-way type, which combined oxygen with the carbon monoxide and unburned hydrocarbons to form carbon dioxide and water. As the science progressed, stricter environmental regulations brought about a change to three-way converters in 1981. These more advanced cats also reduce nitrogen oxide.
Catalytic converters work using a redox reaction. This means that once the catalyst is up to operating temperature (from 500 to 1,200 degrees Fahrenheit) both an oxidation reaction and reduction reaction occur simultaneously. That sounds a little complicated, but it just means that molecules are simultaneously losing and gaining electrons. These types of reactions are extremely common; photosynthesis and rust are both good examples of redox reactions.
In the first stage of the catalytic converter, the reduction stage, the goal is to remove the nitrous oxide and especially the nitric oxide, which when introduced to air quickly changes into nitrogen dioxide, which is very poisonous. The reduction stage works because the nitrogen molecule in the nitrogen oxide wants to bond much more strongly with the metals of the catalyst than it does with its oxygen molecules and the oxygen molecules would rather bond with each other, forming oxygen, which is the type of oxygen that we breathe.
Once the oxygen molecules break off from their nitrogen molecules, the nitrogen molecules move along the surface of the catalyst looking to make friends with another nitrogen molecule. When it finds one, they bond and become the stable, harmless nitrogen in the atmosphere. After it becomes atmospheric nitrogen, its bond with the walls of the catalyst is weakened and the gas moves along to the second phase of the catalytic converter, oxidation.
When the gases have finished in the reduction stage of the catalytic converter, and all the nitrogen oxides have been eliminated, we are left with atmospheric nitrogen, atmospheric oxygen, carbon dioxide, carbon monoxide, water, and unburned fuel.
The oxidation stage of the catalytic converter uses platinum and palladium, which want to bond with the various oxides. The oxygen molecules bond with the surface of the catalyst and break up and eventually find carbon monoxide molecules to bond with, creating carbon dioxide. The carbon dioxide bond is stronger than the bond with the catalyst and moves through the matrix, allowing the process to begin again. While this is happening, some of the freed up oxygen molecules begin to bond with the unburned fuel (hydrocarbons) and are changed to water and more carbon dioxide.
This brief overview of the design of catalytic converters is important because it shows the advancements in cat technology. The original cats were very inefficient and clogged up quickly, causing serious performance issues. Modern performance catalytic converters are designed for free flow while doing their job of cleaning exhaust gases.
Magnaflow makes high-flow cats that meet the requirements of New York and the California Air Resources Board (CARB), such as the 53006 universal 2.5-inch unit. These cats ensure the emissions of your LS or LT swap matches the necessary specs for your area.
To maximize performance, an LS (and any other engine for that matter) needs a strong flow of dense air channeled into the engine. As you well know, when you pack more air into the combustion chamber, you pack in more fuel, and thus, you produce more power. Although mufflers and exhaust systems manage exhaust gases, the air intake determines flow into the engine and it must be tailored to the engine and application.
Unlike the exhaust, the intake system is very simple; an air cleaner element, some tubing, and the MAF sensor are all that is required for the EFI LS and LT engine. It is possible on some swaps to simply install a cone-style air cleaner onto the throttle body with a built-in MAF sensor between them, but usually you need some sort of ductwork.
Large, smooth bends in the piping are the hallmark of an effective intake system; the air should not make abrupt turns. Sharp bends create a vortex effect inside the tube and can drastically slow the air. Slow air means less air in the engine. Short air filter elements require the air to make fast direction changes and that siphons off potential horsepower. The best bet is to make the intake tube as straight as possible, preferably grabbing the cooler air outside the engine bay.
This is not always possible, but most A-Bodies have plenty of room under the hood. For the Chevelle build in this book, a selection of components from Summit Racing and Spectre were used to match the 4-inch Holley throttle body to the 3.5-inch stock Vortec MAF sensor and cone-style air filter. A piece of 4-inch stainless steel tubing was installed between the 90-degree 4-inch silicone elbow for the throttle body. On the other side, a Spectre 4-inch to 3.5-inch stepdown was used to connect to the MAF sensor (I used a 1996 Camaro MAF) and then to the air filter.
Spectre produces vehicle-specific air intake kits for GM A-Body cars as well. These are year-specific and direct the airflow from the inner fender to the throttle body. Unlike universal systems and “piece-together” intakes, these feature smooth mandrel bends that reduce air turbulence and fit like they are factory.
Written by Jefferson Bryant and republished with permission of CarTech Inc
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