Chapter 4 contains detailed information that reveals the correct system and exhaust header type for your engine. This includes primary tube sizing and length, tubing materials and bending, port matching and exhaust header scavenging, the use and advantages of specialty exhaust header coatings, and more.
Chapter 5 delves into the muffler and catalytic converters that are suitable for particular systems and applications. In this chapter I examine specific technology, materials, and intended muffler and catalytic converter application.
Chapter 6 covers exhaust system design and applications specifically for forced-induction applications such as turbocharging and supercharging.
Chapter 7 offers a variety of relative mathematical formulas so you can determine the correct design, size, and components of your exhaust system.
At the end of the book, a Source Guide lists selected manufacturers of automotive performance exhaust systems and components.
The components involved in the engine’s air and fuel intake, combustion, and exhaust process are revealed in this chapter. In order to better understand the function of the exhaust system, it helps to first understand how the air and fuel charge enters the engine and how it is influenced by the chain of events that include intake air, carburetor or throttle body, intake manifold, fuel metering, cylinder heads, camshaft, exhaust manifold or tubular headers, and the engine’s intake, compression, power, and exhaust strokes.
A rule of thumb is to determine engine intake volume and then approximately match this volume for the exhaust. This begins by selecting the appropriate intake manifold and carburetor size, as well as other variables such as cylinder head intake port volume, camshaft profile, and compression ratio. Factors such as these can affect your choice of header primary tube diameter and exhaust pipe diameter. In simple terms, as you generate more cylinder pressure and horsepower, additional exhaust volume likely needs to increase in order to accommodate the engine’s capability to breathe.
Cool intake air is denser than warm air. Higher air density means more oxygen molecules, which provides more intake air charge and more power. Obviously, the more air you can draw into an engine the more horsepower it generates. A cold-air intake refers to an air inlet system that feeds from air that is cooler than the air inside the engine compartment. The farther away from the engine’s heat, or the more isolated the air is from engine heat, the cooler the air that’s available to feed the engine.
A cold-air filter connects to the engine intake with ducting, relocating the filter element farther away from the engine heat source, placing the filter close to a colder fresh-air source. Cold-air systems are offered for specific vehicle applications, with a cold-air shroud that helps to capture more air directly to the filter. (Photo Courtesy K&N Engineering)
One often-ignored aspect is using a cold-air intake. It is an open-element air filter that’s located close to the ground, but it runs the risk of creating a hydrolock in the engine. This can occur if the air filter is exposed to excessive water (for instance, when driving though high-standing water where water may be drawn directly into the intake system). If water enters the engine and makes its way to the combustion chambers, it is possible for the water to build to the point where it prevents the pistons from reaching top dead center (TDC), creating a hydraulic lock. Remember that while you can compress air, you can’t compress a liquid. If hydro-lock occurs, it can take the engine out in a big way, including bent connecting rods, destroyed rod bearings, busted pistons, and more. Unless the vehicle is to be street driven only in dry weather, or used only on a drag strip, locating the air filter(s) low and close to the ground isn’t an issue. If you plan to operate in wet conditions, be aware of this.
The air intake system on this drag-race car’s LS7 engine, built by Hutter Engineering in Chardon, Ohio, is both efficient and gorgeous. The ducting that feeds air to the throttle bodies is fabricated using carbon-fiber tubing. Cold air is routed from the nose of the car directly to the engine, with no engine-bay hot air entering the intake airstream.
A cone- or barrel-style air filter may also allow establishing a cold-air intake for universal applications, such as in race car engine bays. While still within the confines of the engine bay, this filter has been located farther away from the engine.
Air filter elements ideally should be as large (in terms of surface area) as possible, limited primarily by the confines of the engine bay. Inexpensive air filters sometimes provide excessive restriction. Even if they offer acceptable flow, cheap paper elements may not provide much in the way of usable life. It’s best to buy superior filters when the budget allows. Some filters are designed to be reusable; they require washing and drying before placing them back into service. (Photo Courtesy K&N Engineering)
The intake system, including air intake and carburetor (or fuel injection system), has a direct impact on airflow through the engine and subsequently the flow capabilities of the exhaust system. Always keep in mind that what enters the engine also needs to leave the engine. Engine analysis software tools, such as Ricardo and others, provide assistance in developing a system to determine cross sections and volumes from the air filter inlet to the exhaust collector outlet.
A carburetor’s job is to deliver the air/fuel mixture that the engine requires for any given state of engine operation. The carburetor