The intake system’s job is to regulate the flow of clean, filtered air at the right temperature to the engine and to provide vacuum to operate other devices. Most factory intake systems are designed to generate as little noise as possible. The intake system also pulls crankcase vapours into the intake stream so the engine can burn them. Older carbureted engines do not have much of intake system. Usually just an air filter mounted on top of the carburetor, which is mounted on the intake manifold is enough for those engines. Modern day vehicles have much more intake plumbing to accommodate smaller engine bays which have much technology more packed into them.
Intake Air Source Location
Most modern intake designs will take air from a location outside the engine bay to get the coolest air possible. It must also be a place that will not be submerged in water or be pugged up with excessive amounts of dirt or debris. One popular design from “back in the good old days,” is the “Ram Air” intake design. This design uses the movement of the vehicle to force more air into the intake system.
Airbox and Air Filter
The airbox houses the air filter. Some airboxes (still) will have a flap in them, which can pull in warm air from near the exhaust manifold when the engine is cold. This improves fuel atomisation on a cold engine and helps the engine get up to temperature faster. The air filter is a folded paper material with a seal around the outside which catches dirt and debris that enters the intake system before it gets to the engine. Allowing dirt into the engine is extremely harmful to the engine and can shorten an engine’s life dramatically. If there are any holes in the filter element or if the outer seal doesn’t seal properly, dirt is being drawn into the engine. An easy way to check if the air filter is clogged is to hold it up at the sun and see if you can see light through it. If you can still see light (without obvious holes), the filter is still good. The owners manual or maintenance schedule will indicate when these should be replaced but a good general rule is once or twice per year. Drivers that live on a dirt or gravel road, or live in a particularly dusty area may want to have their air filter changed more often.
Intake pipes are much larger than coolant pipes. They allow air to flow from component to component in the air intake system. These must be airtight and have airtight connections to avoid unmetered air and/or dirt and debris from entering the air stream. The pipes must also be flexible or at least have flexible portions to accommodate engine movement. Pipe routing can range from fairly simple on a small 4-cylinder to very complex on a turbocharged engine.
The throttle body controls airflow into the engine. They can be controlled by a cable attached to the accelerator pedal or electronically by the PCM. For more on throttle bodies, check out our engine management page.
The intake manifold is the last piece of the intake system that air travels through before the intake port. Its main purpose is to provide equal amounts of air to each cylinder but it also provides a vacuum source for the power brakes and anything else that uses vacuum. Modern intake manifolds are aluminium or plastic to reduce weight. Plastic manifolds are prone to cracking, especially on a turbocharged engine. One important factor in intake manifold design is runner length. Long and/or skinny intake runners increase air speed into the engine which causes the air and fuel to mix better and produce torque at low-mid engine RPM. The the faster an engine runs, the more air it needs. At high engine RPM, air will already be moving very quickly into the engine. Air speed is not as much of a concern as air volume in the high RPM range. To get the best intake air volume and high RPM horsepower, wide and/or short intake runners are best. On a multiport injection system, the fuel injectors are seated in the lower part of the intake manifold but they spray fuel into the intake port. Some intake manifolds have coolant running through them to heat the air entering the engine. This is done to assist in fuel evaporation when the engine is cold. If coolant leaks into the intake manifold it can cause severe drive-ability issues, white smoke out the tail pipe as well as the possibility of hydro-locking the engine.
Variable Intake Runners
Many vehicles have variable length intake runners so the engine can have the best of both worlds. At low engine RPM, the intake runners will be longer to increase air speed. When the driver demands WOT at high engine RPM, the runners will move to the short position. Different manufacturers have designed different ways of creating variable intake runners. Some systems actually have 2 separate runners per cylinder and an actuator that controls which runner length the intake air charge is allowed to travel through. Other systems allow air into a chamber at the centre of the intake manifold. The intake runners run along the sides of the manifold. The centre chamber rotates to control where the air is allowed to enter the runners. This allows the system to fine tune runner length according to system demands.
After-Market Intakes and High Flow Air Filters
There is much debate around the internet about CAI performance intake systems and high flow air filters. The idea behind these products is that the lower the resistance to airflow into the engine, the more air (oxygen) will enter the engine. This can also be described as an increase in volumetric efficiency. The more air that enters the engine, the more fuel can be burned. This will increase a vehicles maximum power output. First of all, I would like to point out that this will only be of use at WOT. When the throttle is not fully open, the throttle plate is restricting airflow into the engine (no that doesn’t mean you should remove your throttle plate!). No matter how much you decrease airflows resistance before the throttle plate, airflow is still at the mercy of the throttle plate. The throttle plate is there because an engine will pull in more air than it needs or can handle, if it is allowed to at lower RPM. The only time an engine will struggle for air is at WOT and high engine RPM. This is where “a little more airflow” may be of some benefit. Keep in mind that the vehicle manufacturer has already designed the factory intake system to allow sufficient airflow into the engine at all RPMs. The biggest “performance” difference with these systems will be an increase in throttle response, which I describe as a “snappier” throttle. Please note that this does not increase actual power output. Also be aware of your local laws, some of these systems are illegal in some areas.
As for the actual products, I will start with drop in high flow air filters. These products sit in place of the factory air filter, and uses the factory airbox. These can range from about $20 to $100 and will usually claim to produce 2-10hp over the stock air filter. I would like to point out that a vehicle could vary 10hp on a dyno simply from outside air pressure and/or temperature. The 10hp gain could also be simply from removing a clogged air filter and installing a new one. It may have been a maintenance issue that has nothing to do with the actual performance product. Most people who install these will notice a “snappier” throttle, but no noticeable power gains compared to a clean paper filter.
Short Ram Intakes (SRI)
These systems are usually a small amount of piping and a cone air filter that replaces the factory airbox and some of the factory intake hoses. They will usually have the cone air filter sitting where the stock airbox was located. These systems will cost more than a drop-in air filter and will usually claim about 8-15hp gains. The factory’s intake system will most likely take air from an area outside of the engine bay while these systems take air from inside the engine bay, the hottest place possible. Cold air is more dense than hot air, so in a way this could be considered a down grade to the factory system. The “extra air” that the system allows into the engine is hotter and therefore less dense than the air the factory system would have let in. In this way, short ram intakes actually work against themselves. They will usually cause a much “snappier” throttle, which many drivers can interpret as “more power.” The only time “more power” should be noticed with these products is at high engine RPM. In the real world, short ram intakes do not live up to the advertised gains. It is very likely that when the test vehicle was on the dyno, the hood was up with fans running. This allows the short ram to pull in cool air for the test. This will not be the case when the kit is installed on a vehicle and that vehicle is driving down the road. One possible benefit of these systems is the overall sound of the engine. At WOT the engine will sound much deeper and louder. This sound can also be controlled, unlike the sound of a loud exhaust. When cruising, the engine can be kept almost as quiet as factory, but when accelerating hard the engine sounds very lively and aggressive with this type of system.
Cold Air Intake Systems (CAI)
Cold air intake systems are a longer pipe that leads to a cone air filter usually located outside of the engine bay to get the coolest air possible. Some CAI intake systems still take air from inside the engine bay area. They will use sheet metal and the vehicles closed hood to seal out hot air from the engine bay. Some designs accomplish this better than others. These systems can cost over $200 and will usually claim 10-20hp gains. These systems are designed to allow more air into the engine than the factory system and also take in cooler air from outside the engine bay to get the best of air volume as well as air temperature. They will make an engine have a “snappier” throttle with a controllable deep loud sound just like a short ram intake. The only real difference is where the systems take air from. This is an improvement over the short ram design. One problem with some CAI systems is, depending on where the cone air filter is located, the filter may suck in water. This can hydrolock the engine, resulting in the engine needing to be replaced or rebuilt depending on how much damage is done.
Intake Modification on a Turbocharged Engine
A turbocharger forces more air into the engine than the engine would normally take in. The factory intake system is already designed to accommodate this extra airflow. On modern systems, boost levels are monitored by the PCM. The PCM will not allow more air/boost into the engine than the programming allows just because an intake systems is installed. They system will simply back off the turbo. However, the “snappier” throttle effect should be much more noticeable on a turbocharged engine. Also, intake systems work well as a supporting mod for turbocharged engines. For instance, an intake, a bigger downpipe and a chip/flash will normally produce more power than a chip/flash alone. This will of coarse vary from model to model. Also, I do not recommend a short ram intake on a turbocharged engine. Taking warm air from under the hood, running it through a HOT turbocharger where it is compressed and becomes even hotter makes your intercooler’s job very difficult. For more information on turbo and superchargers check out our turbo page.
After-Market Intake Recap
A drop-in filter will not give any noticeable gains, a short ram takes hot air from under the hood instead of a cool air location and finally, the CAI is the best out of the three systems but also costs the most and runs the risk of sucking water into the engine if poorly designed. In the end, none of these systems (alone) are worth the money although they do have their place. To get the most out of an after-market intake system, it should be used as a supporting mod or used along side several other mods to make it worth while. If you are considering buying one of these, I would recommend a brand that does not use oiled filters. There is debate over whether the oiled filters cause damage to MAF sensors. You can make your own decision, but if you can buy a product that MAY be harmful to your MAF and a product that will not be harmful to your MAF, I think the choice is obvious. Also, buy a system that is made specifically for your make, model and engine. This way the install should be fairly straight forward and all emission equipment should be accounted for.
Bottom line: If this is your only modification to your vehicle, you will be disappointed in the performance gains for the cost. However, they do work well as a supporting modification.
The purpose of the exhaust system is to help remove used up exhaust gasses from the cylinder, deliver these gasses to the rear of the vehicle to prevent the occupants from breathing them and also to reduce engine noise in the cabin. The catalytic converter also acts as the vehicles primary emission control device. The gasses that flow through the exhaust system contain many different pollutants that can be harmful if inhaled or even fatal if continuously inhaled. It is important that if you suspect an exhaust leak on your vehicle that you get it looked at as soon as possible for your own health.
The exhaust manifold is the first exhaust component the exhaust gasses encounter after the exhaust port. It collects the exhaust gasses from all the cylinders on that bank and directs them to the downpipe, flex-pipe or the catalytic converter.
Since modern engines have the valves and ports located above the cylinders and the exhaust runs underneath the vehicle, a downpipe is used to direct the exhaust gasses downward. The downpipe can be part of the exhaust manifold or it can be a separate piece that has the flex-pipe and/or catalytic converter located on it. The downpipe is really just a generic term for the piece of the exhaust that carries the exhaust gasses under the vehicle.
The catalytic converter is the primary emission control device for the vehicle. For information on how a cat improves tailpipe emissions, check out our emissions page.
Just like the intake system, the exhaust system has to deal with engine movement. To do this, exhaust systems will use a flex-pipe that acts as a pivot point for the exhaust system. Because of the added load, they are a common area for the exhaust system to leak. Flex-pipes can be cut out and a new one welded in on some applications but others will need to be replaced as a unit with the adjoining pipes and components.
Exhaust clamps provide a way to seal two exhaust components together. Two styles are commonly in use. The most popular is the U-type clamp. To use this type of clamp, one pipe must be able to slide over the other pipe. The clamp then crushes the outer pipe into the inner pipe. The use of this clamp makes it very difficult to separate the pipes in the future if the system needs to be serviced again. The other type of clamp is the sleeve clamp. The sleeve clamp is used on two pipes that are the same size. This type of clamp squeezes both pipes but does not crush or damage the pipes. This makes it very easy to separate the pipes if the system needs to be serviced in the future. I recommend sleeve clamps where ever possible.
Mufflers are used to reduce engine noise. Most vehicles will have one or two mufflers per exhaust system (duel exhaust). Mufflers tend to be located more to the rear of the vehicle. There are two main types of mufflers, reverse flow mufflers and straight through mufflers. Reverse flow mufflers force exhaust gasses through a series of chambers which cause the gasses to zig-zag through the muffler. This type tends to muffle engine noise much better than a straight through type but will be more restrictive. A straight through muffler will allow exhaust gasses to travel straight through the muffler with holes that expose the exhaust to sound baffling material.
Heat shields are designed to protect the body of the vehicle as well as other components from the heat of the exhaust system. These will commonly rattle on the exhaust system over time. Under no circumstances should these be removed from the vehicle. Believe me, if the manufacturer felt that the vehicle would be safe with out them, they would have saved themselves the money and left them off. There can also be a heat shield located on the bottom of the catalytic converter when the cat is located under the vehicle. This is there so the air passing under the vehicle doesn’t cool the cat while driving.
The tail pipe(s) carry the exhaust gas from the last exhaust component out to the rear of the vehicle where is is exposed to the atmosphere. Manufacturers will commonly use the tailpipes as a styling point of the vehicle. They will make the tip of the tailpipe bigger than the rest of the exhaust system to make the vehicle look like it has a larger exhaust system than it actually has.
Dual Exhaust Systems
A true dual exhaust system is two separate exhaust systems for the same engine. This is commonly done on V-type engines because the there already has to be two separate exhaust manifolds, one for each bank of cylinders. The exhaust gasses for each bank will run in a separate exhaust system, side by side, all the way to the rear of the vehicle. Both systems will have their own catalytic converter, muffler and tailpipe. This type of exhaust design can also be visually appealing to the rear of the vehicle. Two (or four) exhaust tips coming out the rear of the vehicle, one on each side, can really complement a vehicle. This is why many manufacturers have a single exhaust that splits in the middle or at the back to create the illusion of a dual exhaust.
Condensation/Water in the Exhaust
A little bit of condensation or water in the exhaust, especially after cold starts, is normal. Remember that hydrogen and oxygen are present in the exhaust gasses. These can combine together to form water vapour (H2O). After a cold engine start, the hot exhaust gasses pass through cold exhaust pipes. This causes the water vapours to condense onto the pipes. This will stop as the pipes begin to heat up and the water droplets are pushed out of the exhaust system. Some mufflers have small holes in them which allow the water droplets to escape.
Exhaust Performance Upgrades
Many people believe that upgrading the exhaust system to increase engine power simply involves installing bigger pipes to allow the exhaust gasses to exit the cylinder with less resistance. It really isn’t that simple. Many exhaust modifications can actually cause a noticeable REDUCTION in overall engine power. Manufacturers design exhaust systems to allow the best balance of performance, cost and noise levels that make sense for the vehicle they are designing. That, under no circumstances, means that louder is better! Do your research and see what worked for other people with your make, model and engine before spending money on an exhaust “upgrade.”
Headers replace a factory exhaust manifold. A factory exhaust manifold may simply allow all the cylinders exhaust gasses on the same bank to flow into a common chamber before flowing into a common downpipe. This design can cause exhaust back pressure from one cylinder to restrict the flow of another cylinder. Many engines will come with a header from the factory. A header has separate pipes from each exhaust port to isolate the cylinders back pressure from each other. Also, after the piston has pushed the exhaust gasses out of the exhaust port, the gasses continue to flow down through the header with momentum. With the exhaust valve closed, nothing can fill the negative pressure area. This creates a slight vacuum in the exhaust port that assists in pulling exhaust gasses out of the cylinder when the exhaust valve finally does open. This of coarse all happens in a fraction of a second and would not be possible with a common exhaust manifold. The header pipes for that bank will eventually come together at a place called the collector. You will see many headers that seem to bend a twist all over the place in what seems like a pointless mess. This is done to make all the header pipes a specific and equal length.
A bigger downpipe on a naturally aspirated engine will typically not give you big gains unless the factory downpipe was particularly restrictive. They are most useful when installed with a well designed, full exhaust system.
Factory mufflers are designed to absorb as much sound as possible without causing a performance altering restriction. Simply installing a loud (fart can) muffler in place of a factory muffler will not cause any kind of worth while gains. They may seem like a good idea when you install them, but the next time you have to go on a long trip, you will regret it. If you think people are looking at you and thinking “Man, what a sick fart can!” They are not. Now as for a reasonable performance muffler or exhaust system that makes the engine sound a little deeper without being obnoxious, that is a different story. Check out YouTube to see what different engines sound like with different performance mufflers or exhaust systems.
Upgrading the Exhaust on a Turbocharged Engine
Turbocharged engines respond much better to free flowing exhaust systems. The faster the exhaust gasses can get in and out of the turbo the better. The equivalent of a header on a turbocharged engine would be a tubular exhaust manifold. These are not commonly made for stock turbos. They are mainly used when a bigger turbocharger is installed. Turbochargers respond well to a large downpipe. They can increase (possible) boost levels as well as decrease turbo lag. A larger diameter cat-back system can also improve a turbochargers efficiency when used along side a larger downpipe and high-flow cat. This is called a turbo-back exhaust system.
Cat-Back Exhaust Systems
A cat-back exhaust system is an after-market exhaust system that replaces the exhaust system from behind the catalytic converter to the rear of the vehicle. These systems are designed for sound more than performance. All the sock mufflers will be replaced and the system will most likely use larger diameter exhaust pipes.
Full Exhaust Systems
Full exhaust systems replace the entire exhaust system. Manifold, downpipe, catalytic converter, piping and mufflers are all changed. These systems will be more expensive but they may offer some significant performance advantages as well as sound.
A straight pipe may refer to one exhaust component being replaced by an exhaust pipe, such as a catalytic converter or a muffler. It can also mean that the entire exhaust system has been replaced with exhaust pipes only. No cat or mufflers. Straight piping a cat will cause a vehicle to fail an emission test as well as illuminate the check engine light if it has a downstream O2 sensor. It is also illegal to drive a vehicle like this in most areas as the vehicles primary emission component has been eliminated. Straight piping a muffler will cause an engine to run extremely loud all the time.
Dual Exhaust as an Upgrade
This can be done as a performance upgrade to some V-type engines. Exhaust gasses will flow better through two separate 3″ (76.2mm) pipes than it will through one 4″ (101.6mm) pipe. Some engines will respond well to this upgrade and others will not. Some may even loose power.
After-Market Exhaust Recap
Exhaust upgrades can allow an engine to produce more power as well as sound better but they can also reduce engine power. Do your research and find out what really works for your specific make, model and engine before spending your money. Make sure you can deal with the loud noise all the time if you are going with loud exhaust system. I would recommend buying name brand exhaust components, cheap metal will rust away quickly. Exhaust upgrades also work well as supporting upgrades, or along side several other mods.