With most modular engine swaps, space restrictions under the hood of the swap vehicle will affect the exhaust system. Often, components can contact and interfere with the routing of the header tubs or exhaust manifold castings. When building a high-performance car, owners often opt for headers to allow the engine to breathe well and produce optimal horsepower for the application. Owners can either buy off-the-shelf headers or have custom headers fabricated for their project car. Proper planning and positioning of the engine should allow you to use off-the-shelf headers in most cases, but in some special applications and certain vehicles you may have to have headers fabricated. You must trial fit the headers to the engine and chassis to verify if there’s any contact between the headers and the brake booster, steering rod, suspension parts, or any other component. If you find a clearance problem, you need to consider all the options and select the best one for the project.
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Factory Exhaust Manifolds
Because exhaust ports have changed frequently on modular engines, aftermarket solutions for conversions have been few and difficult to find. Depending on the chassis, modifications to an existing design may be required to properly fit the exhaust system. The Coyote platform has become very popular, so some good conversion systems have come out in support of the 5.0.
Aftermarket Exhaust Manifolds and Headers
The aftermarket offers cast-iron manifolds, shorty headers, midlength headers, and long tube headers. The choice between these manifolds depends largely on the exhaust-port design of the engine and the available engine compartment space. The cast-iron manifolds provide the greatest amount of room for tight engine compartments. Shorty headers have two advantages over cast-iron manifolds: they generally flow a little better, and they can be modified if necessary.
Mid-length headers are designed to follow along the top of the exhaust line and then drop down to run under the body. In the 1960s, headers were designed to have the pipes drop down almost immediately, but this conflicts with many of the modern steering systems, including rack-and-pinion conversions. Where most shorty headers are designed to exit at the same location as stock manifolds (and thereby use stock exhaust outlets if needed), the mid-length headers pull the outlet to the back of the engine a little farther and may provide clearance in some chassis configurations.
Full-length headers are available, but they are often purpose-built for specific applications. Like the mid-length headers, most new designs go up and back rather than straight down and back. This helps with clearing steering and engine-mounting components. Unless your application has specific headers made for the conversion, fitting the headers may be trial and error, as most header companies don’t publish dimensions.
Conversion Headers and Header Components
Several companies are now offering headers specifically designed for engine and chassis combinations, and this list continues to grow as conversions become more popular. Doug’s Headers, Detroit Speed, and Mustangs to Fear offer full-length headers for 19641⁄2–1973 Mustangs. Several companies, including American Racing Headers, BBK, and Kooks, now make Coyote conversion headers for the Fox body. Because the early Mustang frame is narrow, these headers may fit other narrow chassis.
If a sufficient exhaust header can’t be found, companies are now providing the components for your header builder to build you a set from scratch. Stainless Steel Works sells a complete line of stainless-steel flanges and pre-bent tubing that can be used to fabricate your own headers. Dynatech and Kooks also sell its flanges separately so you can build your own exhaust.
Ford has installed two types of catalytic converters on its vehicles. Two of the converters are a three-way type while two other converters are conventional. They use different honeycomb internals to scrub hydrocarbons, carbon monoxide, and nitrogen oxides from the exhaust gases.
Because the exhaust flows over the ceramic surface inside the converter, smaller is not necessarily better. A smaller converter has less surface area and won’t support larger engines and output.
By law, factory catalytic converters are required to last 80,000 miles, so they are generally built well to last the warranty period. In general, aftermarket converters must last 5 years or 50,000 miles, so most of your aftermarket units are made to the same standards. Laws apply to converter installations that do not meet OEM specifications, so check the local laws before selecting your converter.
Because of the conversion process, catalytic converters generate a lot of heat. Factory-style converters are wrapped in a stainless-steel shield, and some aftermarket units do not use the shield to save space. This should be taken into consideration when designing the exhaust layout. Also, single converters may not perform as well as the original system due to the different honeycomb internal makeup of the two style converters.
Choosing the right converter has a lot to do with the laws in your area. Some exhaust manufacturers will make exhausts only from the catalytic converter back because dealing with the regulations is difficult. Magnaflow and Flowmaster both sell universal converters and may be the best choice when designing your exhaust system. They are knowledgeable on the laws in your area and can help you build the correct system. Kooks also makes a universal converter, but be sure to check your local regulations first. It may be best to choose your converter as a complete system rather than as a universal product.
Ford uses four oxygen sensors from the factory. Two are mounted before the converter and two after, so the fuel/air ratio is measured as well as the efficiency of the catalytic converter. The computer can measure the exhaust gases after they have run through the converter and adjust the fuel/air output to improve emissions. Some early systems used two heated and two non-heated oxygen sensors, but eventually Ford changed to four heated sensors. The oxygen sensor is designed to work in the exhaust-gas temperature range, and heating them brings them into this range faster and makes them more efficient.
Oxygen sensors have become more and more sophisticated over the course of the modular engine run. Early sensors had two wires, and the newer ones can have five wires or more. Typically, the more wires coming out of the sensor, the more complex they are to test. When selecting oxygen sensors, make sure they work properly with your engine computer. Some aftermarket engine computers require you to run a specific oxygen sensor.
Wide-band and narrow-band oxygen sensors are offered to regulate air/ fuel ratios. The very first oxygen sensors were designed to tell the computer if the air/fuel ratio varied from the ideal ratio of 14.7:1. That ratio means that there is sufficient air to burn all the fuel, and this ratio is referred to as the stoichiometric mixture, or stoic mix. If the mixture has too much air the mixture is considered lean, and the burn is hotter and can damage components. If the mixture has less air it is considered rich, and the burn is cooler and less efficient.
Narrow-band oxygen sensors tell the computer if the mixture is stoic, lean, or rich, so the computer can adjust the mixture to try to correct the ratio. However, the sensors can’t communicate the specific lean-ness or richness to the computer; rather, these sensors communicate just lean or rich condition.
Wide-band oxygen sensors measure fuel/air ratios wider than the stoic mix, and this information can help the computer and tuner better tune the engine. Some narrow band sensors are still used behind the catalytic converters, but most oxygen sensors (and ones used in performance applications) are the wide band variety.
“Cat-back” is a simple way of saying everything after the catalytic converter. Here, manufacturers have a little more leeway with design than with the converters. Some areas have strict noise regulations that penalize any change to the mufflers from OEM. Be sure to check local regulations prior to selecting an exhaust system.
As with getting air into the engine, bigger isn’t always better on the exhaust system. The larger the pipes, the slower the exhaust gases flow through them, and the more the engine works to push those gases out of the exhaust. With less pressure, exhaust gases can begin to swirl around and disrupt the flow and cool. When the exhaust gases cool, they become denser, and the engine has to work harder to force the denser gases out. Most exhaust systems in stock form suffer from undersized exhaust manifolds and headers, which forces the engine to fight against the restriction. Err on the side of larger pipes.
Ford has used 409 Stainless in its exhaust for most of the modular engine run. 409 stainless is a combination of mild steel and stainless steel, and it has some of the qualities of both metals. It bends easier than stainless, and does not rust out nearly as fast as mild steel. It typically turns brown rather than rusts. Mild steel is easy to work with but rusts over time, and stainless exhaust systems are made from pre-bent tubing that is usually welded together. Some of the larger exhaust companies offer fully bent one-piece exhaust systems.
Swap Spotlight: 1968 Torino
This 1968 Torino is all home built and done on a meager budget. Craig Wood and Jeremy Keller of Windsor, Canada, decided to build a pair of 1968 Torino GT fastbacks: one with conventional vintage iron and one as a modern, updated powerplant. Just because the build was low-budget doesn’t mean these guys didn’t do the job well. The amount of engineering involved to create their car is extraordinary. Turns out Craig and Jeremy work in the automotive field as engineers, so they were fully aware of what it would take to make the project a success. And the results are amazing.
The Torino is equipped with a 4.6 SOHC pulled from a 2001 Mustang GT, but it certainly isn’t stock. A modified Roush Stage 3 supercharger and 73-mm pulley kit give it a serious boost in performance, and Torino is infused with a lot of parts from the 2004 SVT Cobra. The front suspension uses a K-member and towers grafted to the original Torino frame rails, and the engine compartment panels were adapted to the new strut towers. From there, the stock SN-95 spindles were fitted with 14-inch Alcon rotors and calipers. The 2004 Cobra rack-and-pinion is mated to the original steering shaft with a modified F-150/ Lincoln Navigator steering shaft. Braking to all four corners is handled by a 2004 Cobra hydroboost system.
The transmission was sourced from a 2004 Cobra in the form of a T-56 6-speed. The clutch is a cable release design and a Steeda Tri-ax shifter is used in a modified tunnel conversion cover. An aluminum driveshaft from a Crown Victoria police car fit perfect with the setup and drives the power through a 2004 Cobra independent rear suspension fitted with 3.55 gearing.
The computer is a factory EEC-V system with a 2004 Roush tune and stock SN-95 Mustang wiring harnesses. This allowed for the use of all the SN-95 components on the Torino frame. Some of the real engineering in this build happens under the dash. The complete HVAC system from the 2004 Cobra was grafted to the Torino firewall, and then the controls were grafted to the original Torino control unit. The gauges are modern and based off the 2004 dash and electronics. The boys used an in-dash ignition switch from a Ford Thunderbird, and then custom grafted the Mustang electronics to fit the Torino gauge cluster compartment. The result is an instrument panel that can take full advantage of the Ford PATS system, cruise control, keyless entry, late model speedometer, and intermittent wiper system.
A 2004 Cobra dual fuel pump was custom grafted into a stock Torino fuel tank and baffles were added to assist the pump. A Moroso road racing oil pan was used for the extra capacity, and oil is cooled through an Earls oil cooler. A Magnaflow exhaust and X-pipe were used along with a Magnaflow outlet pipe made for a Cobra IRS, with custom exhaust tips added to fit the Torino chassis.
The GT rides on a set of Roush 18-inch forged chrome-plated aluminum wheels originally used on the 2009 Roush P51B edition Mustangs. Michelin Pilot Sport tires ride on all four corners with 18 x 9–inch rims with 275/35/18 tires up front, and 18 x 10–inch wheels with 315/30/18 tires at the rear.
The Torino is currently finish in a stealthy flat black, which may be changed in the future. And don’t think this car is for show only, one of the first trips out for this beast was Gingerman Raceway in South Haven, Michigan, where it performed quite nicely, thank you very much.
Craig and Jeremy’s 1968 Torino GT is a testament to the fact that you can build a car on a budget and do an amazing job. With patience, seeking out the right knowledge, and finding the right parts at the right price, you, too, can build something no one else has and make it turn heads wherever it goes.
Written by Dave Stribling and Posted with Permission of CarTechBooks
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