Jul 06, 2008 - Intake and Exhaust Systems: Gasping for Horsepower

As living beings, you and I are constantly breathing in and out – inhaling the fresh oxygen that our internal parts require to function, and exhaling the poisonous wastes, i.e. carbon dioxide, that our bodies produce from natural operation. Internal combustion engines, or engines powered by gasoline and diesel, breathe in a very similar way! A knowledge of intake and exhaust systems is key to modifying your vehicle to perform better, both as a daily-driver and as a street-racing machine.

SOUND FILE: Inside a garage -- a restrictive stock LT1 exhaust versus a performance LT1 exhaust system.

Table of Contents

1. Engine Intake System Explained
2. Engine Exhaust System Explained
3. Factory Stock Intake and Exhaust Systems Kill Horsepower
4. Intakes and Exhaust: Why Upgrade?
5. How to Upgrade Your Vehicle’s Air Intake System
6. How to Upgrade Your Vehicle’s Exhaust System
7. Real-Life Results

Engine Intake System Explained

All fires and explosions, including the controlled gasoline or diesel explosions occurring inside your car, truck, SUV, or motorcycle engine, require oxygen in order to occur. What happens if a jar is turned upside down and placed over a burning candle? After the candle flame uses all of the available oxygen in the jar, which happens quickly, it will expire and the candle will burn no more. Without oxygen, the electrical spark from the spark plugs in your gasoline-powered vehicle would not be able to ignite the gasoline vapors -- the internal gasoline explosion that creates the energy to drive the vehicle would not occur, and the engine would refuse to start, or it would stall/die if it were running already. Because diesel does not explode under spark or flame like gasoline does, diesel engines do not rely on spark plugs to create their driving motion –- instead, diesel engines compress the diesel and oxygen together under high pressures to create an explosion. While the functioning of a diesel engine is different from that of a gasoline engine, oxygen is just as important in creating the explosion in either type of engine. The seldom-seen rotary engine, or Wankel engine (developed by Dr. Felix Wankel), transfers the power/energy of the gasoline explosion into motion in a different way than the popular piston engine, but the rotary engine still requires fuel (gasoline) and oxygen to create an energetic, driving explosion.

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Engine Exhaust System Explained

One of the unchanging physical laws of our universe, known as the “law of conservation of matter”, states that matter cannot be created nor destroyed –- it may only be rearranged. What is matter? Matter is the stuff that makes up the building blocks of our universe. If you can touch, taste, or smell something, it is made up of matter. Gasoline (or diesel) and oxygen are made up of matter. Your computer, desk, and chair are made up of matter. The pizza you had for dinner last night (and probably breakfast this morning) is made up of matter. So, if matter cannot be destroyed, what happened to the slices of pepperoni and extra cheese that disappeared out of the box last night? Your body converted some of the pizza matter into the energy that drives your body, and the rest of the pizza matter was converted into the solid and liquid waste that you have expelled or will expel from your body later today. The pizza still exists, just in different forms. This is exactly what happens when the gasoline (or diesel) and oxygen combine in your engine and explode! The explosion is a result of the gasoline and oxygen being converted to energy, which your vehicle’s engine then uses to push or pull the big hunk of metal and plastic that is your car, truck, SUV, or motorcycle down the road. However, the process is not 100% efficient –- in other words, only about 80% to 90% of the gasoline and oxygen actually converts into the explosive energy that drives your vehicle. The other 20% is converted into waste –- harmful gasses (i.e. carbon monoxide) and other material that must be removed from the engine. Much like the excretory system (intestines, bladder, etc.) in your body, it is the job of the exhaust system to remove this waste from the engine. If the carbon monoxide and other waste were not removed from the engine after each explosion, then the engine would quickly fill with this waste, and there would be no room for fuel and oxygen to enter into it to provide the next explosive “oomph”. The vehicle would stall, or “die”, in much the same way the human body would fill with waste and die if its excretory system stopped functioning.

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Factory Stock Intake and Exhaust Systems Kill Horsepower

Yes, it's true -- factories install restrictive intake and exhaust systems on new vehicles, ON PURPOSE! Why, you ask? Several factors exist that influence this decision, including but not limited to:

• Cheaper and faster vehicle production
• Limiting vehicle noise output to make the vehicle appeal to the standard consumer
• Limiting vehicle power to cause competition between different vehicle models with the same engine
• Limiting vehicle power output to stay within a certain vehicle or safety classification

YouTube Video: A BMW 335i being dyno-tested after catback exhaust upgrade. 11 horsepower gain!

In order to mass-produce parts cheaply and quickly, machines are used to make quick bends in metal tubing. Have you ever had a garden hose kink on you while washing your vehicle? Well, the same principle applies when bending a hollow steel tube. If you simply grab it and bend it, the inner diameter of the tube at the point of the bend becomes smaller than the diameter of the rest of the pipe. Most factory stock exhaust systems and air intake systems are formed in this manner by machines, in order to produce millions and millions of exhaust pipes quickly and cost effectively. Most performance exhaust components are formed using a process called Mandrel Bending. Mandrel Bending is an expensive way to form exhaust components, but it ensures that all the bends have the same inside diameter as the rest of the pipe. Since your vehicle's manufacturer goal was to produce exhaust components in a fast and affordable manner, your stock exhaust system is likely full of kinks formed by the quick and easy "grab and go" bending process. As the exhaust gasses and other wastes created by your car, truck, SUV, or motorcycle's engine travel down the stock exhaust pipes, they encounter these restrictive bends and the waste is not allowed to properly vent out of the engine. At lower RPMs (during normal driving conditions), this is not a problem. But when you apply throttle to pass, merge on the freeway, or street-race, many more exhaust gasses are created than normal -- if they are not allowed to vent properly, then your vehicle's engine is not producing power to its fullest potential. The same is true for the air intake system, but in reverse. The air intake system feeds your vehicle by pulling in the vital oxygen that's necessary for the gasoline or diesel combustion process that occurs inside its engine. The factory stock air intake system in most vehicles is also "kinked", which prevents your vehicle from receiving the necessary oxygen that is so crucial for the combustion process. The result is the same as described above for stock exhaust systems -- when throttle is applied during passing, merging, and street racing, the engine cannot breathe properly, causing the fuel to burn improperly during the combustion process. In addition to cheaper, faster production of exhaust and intake components, some vehicles are actually made with restrictive components on purpose. Why? Well the most obvious answer is that most consumers do not want their vehicles to make more noise than necessary. When restrictions are removed from the exhaust system, the sound of the vehicle naturally becomes louder, because the sound waves of the explosions occurring inside the engine are allowed to flow through the exhaust system more freely along with the waste. This is not to be confused with resonator (i.e. glass-packed) mufflers and resonator tips, which are specifically designed to amplify engine noise as it exits the exhaust system -- they do not necessarily remove any restrictions from the exhaust flow itself. Air intake systems are actually made restrictive on purpose to control noise as well. Can an air intake really make that much noise? Think of it this way -- the harder you breathe, the louder your breathing sounds. Your vehicle's engine requires large amounts of air to function, especially when you step on the throttle. This would normally result in a loud sucking noise as your vehicle's engine consumes hundreds of cubic feet of air per minute (cubic feet per minute, or CFM, is the unit of measurement for an engine's air consumption rate). To prevent this noise from being noticeable, vehicle manufacturers install "mufflers" on air intake systems, just like they do on exhaust systems. While intake mufflers (known as air silencers or intake silencers) look nothing like exhaust mufflers, the basic concept behind them is the same. Yet another reason vehicle manufacturers produce cars, trucks, SUVs, and motorcycles with restrictive exhaust and intake systems is to purposely limit power output. Sometimes this is done to cause competition between different vehicle models that contain the same engine. For example, the LT1 Firebird Formula contains the same engine as the LT1 Corvette, respectively. If a brand new, $30,000 1996 Firebird Formula's LT1 engine were to put out as much power as a $60,000 LT1 Corvette with the same engine, then the Corvette would have one less selling point over the Firebird Formula. So, General Motors restricted the intake and exhaust on the LT1 engine in the Firebird Formula, causing it to produce about 15% less horsepower than the LT1 engine in the Corvette. Same engine, same car manufacturer – but different intake and exhaust setups. This is actually a common practice among automobile manufacturers, because it is cheaper for vehicle manufacturers to install the same engine in multiple vehicle models, and simply produce different components for each "version" of that engine. Apart from creating competition among different vehicle models with the same engine, automobile manufacturers also purposely restrict power output to ensure that a certain vehicle remains within a certain vehicle class. I’m unsure of real-world values, so the following example is hypothetical -– however, the actual situation occurs frequently. Let's say that a certain family sedan is in the testing phase with a manufacturer before being sold to the public. In this pre-production phase, the manufacturer notes that the vehicle is producing 220 horsepower. Perhaps government regulations and insurance companies classify vehicles producing more than 210 horsepower as sports cars. In its current form, the family sedan this manufacturer is trying to produce has become a sports car -- meaning noticeably increased insurance rates for the consumer and perhaps extra taxes or bad public relations for the manufacturer. Also, the vehicle will now be compared with other vehicles in the sports car class, instead of being compared to other family sedans. What's the easy fix? Restrict the intake and exhaust systems a bit and now the vehicle produces slightly less than 210 horsepower – voila, the family sedan is no longer classified as a sports car in the aforementioned situations! There are many different reasons as to why vehicles are manufactured with restrictive exhaust and intake systems (in fact, there are probably more reasons than are covered here), but one thing is certain -– whether you are a street racer or not, the stock intake and exhaust systems on your vehicle are definitely preventing it from reaching its full performance potential!

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Intakes and Exhaust: Why Upgrade?

Removing the factory restrictions should be your primary concern when upgrading your factory-stock intake and exhaust systems. Spending a few hundred dollars doing this will allow all your engine’s other stock systems to reach their maximum power output potential by facilitating better oxygen flow through the intake and better waste removal through the exhaust, unleashing anywhere from 15 to 50 extra horsepower out of your otherwise unmodified vehicle.

Not only will upgrading your vehicle’s intake and exhaust systems give your vehicle more power now -– it will also pave the way for more drastic engine power upgrades in the future. Suppose that several months from now, you would like to purchase new cylinder heads for your vehicle that are designed to add 50 or more horsepower to the output of your engine. Because more power production means more intense combustion, this hearty upgrade naturally will require more air to enter into the engine and more exhaust gasses to be vented from it. If your vehicle’s stock, restrictive intake and exhaust systems are still installed, they may not be able to keep up with the oxygen intake and waste exhaust requirements of the new cylinder heads –- and you may not see the full power benefit of adding the new cylinder heads. The same is true for any engine modification that results in a significant power increase (i.e. computer, ignition, and fuel delivery upgrades) –- the engine must be able to breathe at the new rate it requires to provide the optimal horsepower and torque output that the new engine setup is designed to produce.

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How to Upgrade Your Vehicle’s Air Intake System

Upgrading your vehicle’s intake system is a rather straight-forward and simple process. It should be achievable by almost anyone with basic hand-tools (i.e. screwdrivers, wrenches, and pliers) and basic technical knowledge/skills (i.e. removing and attaching clamps, tubes, and electrical connectors). Fortunately, many companies exist that manufacture and package pre-fabricated intake upgrade kits for virtually every vehicle and engine on the planet. My favorite brand of intake parts is K&N, but several other companies produce reliable, well-built intake upgrade kits such as Iceman, SLP, and Morosso. Though these kits all produce good results, achieving maximum intake upgrade results requires replacement of some components that do not usually come in the pre-fabricated kits, such as the Mass Airflow Sensor or MAF sensor (sometimes it is called by a different name, but the concept is the same) and Throttle Body. Here are several suggestions to upgrade your vehicle’s air intake system:

• Air Filter Replacement – Simply replacing the stock air filter and bypassing the stock air intake silencer can give slight results, but is not too effective as a stand-alone upgrade.
• Basic Air Intake Kits – These kits replace your stock air filter with one that is capable of achieving higher airflow. These kits also replace the restrictive stock intake tubing and air intake silencer that are robbing your vehicle of power.
• Cold Air Induction Intake Kits – These kits generally include the same components as the Basic Air Intake Kits described above, but the replacement tubing routes the air filter to a location outside the engine compartment, such as the inside of a wheel-well. Chances are your stock air filter or Basic Air Intake Kit is pulling in HOT air from inside the engine compartment. Rerouting the location of the air filter to an area outside the engine compartment allows your vehicle to breathe cooler, denser charges of air –- which equates to a noticeable increase in power.
• Ram Air Induction Intake Kits – These kits are not available for every vehicle and often require expert modification of the vehicle’s hood. This kit follows similar principles as the Cold Air Induction Intake Kit described above, except the replacement intake tubing actually routes the air filter into an open hole on the exterior of the vehicle, usually on the hood, roof or bumper. As your vehicle travels faster, more air flows over the vehicle’s body. A Ram Air Induction Intake Kit “scoops” some of this air into the engine through the open hole on the exterior of the vehicle (the open hole is actually called a “scoop”, for obvious reasons). This “rams the air” into the engine, and produces an even more noticeable power gain than the Cold Air Induction Intake Kit.
• Mass Air Flow (MAF) Sensor – Almost every computer-controlled vehicle has one of these, though it may not be called a Mass Air Flow Sensor on your particular vehicle. If you have replaced your stock intake tubing already, then you have probably touched this sensor. It is usually a rather bulky, square/rectangular metal device that is sandwiched between two pieces of air intake tubing. It also has an electrical connector located on it that feeds it with power and returns a result to the vehicle’s computer. This sensor’s job is to supply the vehicle’s computer with a reading on the amount of air that is entering the engine through the intake tube. The computer then uses this information to regulate the operation of the vehicle. Many stock Mass Air Flow Sensors are bulky and contain restrictive metal “netting” that inhibits proper air flow. Replacing your vehicle’s stock MAF sensor with an aftermarket MAF sensor will allow more air to flow through the intake system, and it will provide better air intake readings to your vehicle’s computer. You won’t necessarily notice a huge gain in power after replacing this device, but this upgrade will become necessary if you decide to do some serious power upgrades.
• Throttle Body – The Throttle Body is located where your air intake tubing meets your engine. It contains one or more holes that are covered by a plate. The harder you push on the gas pedal, the more the plate opens, allowing more air to flow to the engine to produce more power when you press harder on the accelerator. You can replace your stock Throttle Body with an aftermarket one that has bigger openings. However, the bigger openings may not match your current Intake Manifold’s openings. Selecting the correct aftermarket Throttle Body takes a little bit of thought –- if executed properly, this can provide a slight power increase over your stock Throttle Body. However, remember that if you have not replaced the rest of your air intake system, a bigger opening in the throttle body may not necessarily flow more air into the engine. If you’re planning on upgrading your Intake Manifold, make sure to purchase a throttle body that fits the openings on the new Intake Manifold.
• Intake Manifold – This is usually the last piece of equipment that air passes through before it enters your engine and becomes a part of the combustion cycle. Its job is to divert the incoming air through the intake manifold runners contained inside it, delivering that air to whatever cylinder needs it, when it needs it. Stock Intake Manifolds generally contain short and/or crimped/undersized intake manifold runners. Replacing your stock Intake Manifold can produce as much as a 10% increase in engine torque, but you may not see the full power benefit of replacing the Intake Manifold if you have not replaced the rest of the air intake system.
• Forced Air Induction – The process of Forced Air Induction actually involves just that -– using pumps to compress and force large volumes of high-pressure air into the engine. These “air pumps” are known as superchargers and turbochargers. Some cheap superchargers operate off your vehicle’s 12-volt electrical system and provide a small pressure increase that amounts to a 10% to 15% increase in your vehicle’s horsepower output. However, the full benefit of Forced Air Induction can only be experienced by installing a turbocharger or a belt-driven supercharger. These heavy-duty and expensive methods of Forced Air Induction can provide 40% to 85% increases in horsepower. Expect a full article on Forced Air Induction to be released sometime in the future.

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How to Upgrade Your Vehicle’s Exhaust System

Installing an air intake system can be an easy task for even the most novice do-it-yourselfer, but exhaust systems usually require a broader range of tools and knowledge. The removal of a stock exhaust system can be facilitated with the use of a rotary saw (or “Sawz-All”) or other powered cutting tool. A chisel, hammer, and heavy-duty rubber mallet are also some handy tools to have around when performing an exhaust upgrade –- along with your basic screwdrivers, wrenches, sockets, pliers, and ratchet extensions. While I would recommend having your exhaust components professionally installed by someone who is both an auto-mechanic and an exceptional welder, it is possible to perform this task in your own driveway/garage with no welding required (I have done it many times, on many different vehicles). In order to have a freer flowing exhaust system, you must first eliminate the kinks and bends in your vehicle’s stock exhaust pipes. This should be combined with installing a freer-flowing muffler as well. Exhaust mufflers help to drastically decrease the noise emitted by your vehicle. Installing a muffler that increases flow also causes an increase in vehicle noise emissions that can be anywhere from mild to dramatic, depending on the muffler you select (we consumers have quite a selection to choose from in this department). Forunately, many aftermarket manufacturers exist that produce “cat-back” exhaust system upgrade kits. A “cat-back” exhaust system replaces your vehicle’s muffler, tailpipe (the pipe that branches off the muffler and sticks out the back of your vehicle), and all of the exhaust pipes that lead to the muffler from the catalytic converter (a catalytic converter is an exhaust device that contains certain “catalysts” that “convert” harmful exhaust gasses into less harmful waste products). Some vehicles may have multiple mufflers, tailpipes, and catalytic converters -- an aftermarket cat-back exhaust system that has been designed for your specific vehicle will include the correct number of mufflers and tailpipes, and the correct amount of other exhaust piping that has been shaped exclusively to fit your vehicle. While installing a cat-back exhaust system kit is a wonderful start to an exhaust system upgrade, here are some other types of upgrades for your exhaust system:

• Resonator Tips – These are tailpipes that are packed with fiberglass. They are designed to make your vehicle sound louder and more aggressive, but Resonator Tips alone will not provide any power increases. To make your vehicle sound naturally more aggressive and actually provide a power increase, spend your money on a cat-back exhaust system kit with a true power-building muffler instead.
• Catalytic Converters – Catalytic converters use platinum and other metals to reduce harmful emissions in your engine's exhaust. Your stock catalytic converters are extremely restrictive -- replace them with aftermarket catalytic converters to increase exhaust flow while maintaining proper emission controls. Note that replacing your catalytic converters may require you to replace your Oxygen (or O2) Sensor as well.
• Headers and Y-Pipes – When exhaust gasses are ready to escape from the engine, they pass into the first part of your exhaust system – the exhaust manifolds (or headers). It is the job of the header(s) to scavenge exhaust gasses from your engine and pass them along to the rest of the exhaust system. Four-cylinder and other inline engines contain only one header, but V6, V8, V10, and V12 engines contain two exhaust manifolds – one for each side of the engine. In this case, both headers will either combine into one pipe through the use of a Y-Pipe, where they will pass through the catalytic converter(s) and travel down a single pipe through a single muffler, or each header will have a separate piping system that flows through separate catalytic converters and mufflers. Stock headers and Y-Pipes are usually restricted by horrible bending techniques and a lack of “flow technology”. Aftermarket headers and Y-Pipes are shaped differently than stock headers and Y-Pipes, and they are also manufactured using a uniform bending technique known as Mandrel Bending. The design and quality of aftermarket headers and Y-Pipes makes them extremely superior to stock headers and Y-Pipes –- so much so, that upgrading these components can produce dramatic horsepower and torque increases. However, keep in mind that if you replace only your vehicle’s stock header(s) and Y-Pipe (if included on your vehicle) and do not upgrade the rest of the exhaust system, you may not experience the full power increase that the aftermarket header(s) and Y-Pipe are designed to provide.

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Mr. Digs' Firebird with performance intake and exhaust.

Real-Life Results

I have upgraded the air intake and exhaust systems on every vehicle I have ever owned, including a 1992 Ford Mustang GT, a 1990 Pontiac Trans Am, a 1996 Jeep Cherokee, and a 1996 Pontiac Firebird Formula. I received immediate power gains on all of these vehicles –- some of the gains were moderate (the 1992 Mustang and the 1990 Trans Am), and some of the gains were dramatic (the 1996 Jeep Cherokee and 1996 Pontiac Firebird). If you follow the steps outlined above, not only are you guaranteed to feel some power increases now, but you will be paving the way for extreme power-building upgrades in the future! My average per-vehicle cost of upgrading ALL of the components listed above (which is not necessary to feel some good power increases) is approximately $1250. But remember –- though you will receive the full benefits of aftermarket parts once all of a particular system’s stock components have been replaced, you will still gain some power if you upgrade over time, piece by piece!

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