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Intake Guide


INTAKE

There are a variety of intake schemes available depending on which vehicle you are talking about. In general the goals of an aftermarket intake should be to increase airflow and also draw in colder air, if possible. Airflow is generally increased by reducing bends, smoothing the airflow track, and increasing filter surface area. Drawing colder air can be accomplished by placing the inlet out of the engine bay (through a fender), directing cold air to the inlet via a scoop, or placing the inlet in a area within the engine bay that has a relatively low temperature.

Intake length and resonance will not be discussed.

Filter

The simplest way to improve the flow of an air filter without compromising filtering is to increase the surface area. Alternative schemes include creating a filter that combines some sort of meshwork and oil (K&N, Holley Powershot, Fram Air Hog). The latter also achieves greater surface area due to the nature of the material used in its construction (cotton guaze). The cotton guaze and oil setups claim to allow trapping of a larger amount of dirt and debris, which is why they typically recommend 50,000 mile service intervals.

At least as so as the theory goes. In some vehicles it has been shown that certain aftermarket filters not only increase the amount of filtrate that reaches the engine, but they produce less horsepower as well. Many times gains are also overstated by end users who have replaced their entire intake setups while switching filters. In the end an air filter is not a real performance modification, and it is probably best to run a standard paper filter and replace it when it needs to be replaced.

Air Filtration and Flow Test
Note: this test is not the be all and end all of air filter testing; however if you want more information on the subject visit a technical message board or conduct your own research.

Tubes, Ducting, Filter Box

Here is where the real performance gains are achieved. In many OEM applications, the overriding factors for intake design are packaging and noise reduction. For example, 1998-2002 F-bodies employ an “air silencer” after the filter box in order to reduce noise from the intake. Elimination of such devices, unnecessary bends, and irregular surfaces can all result in increased intake flow potential. If possible, also choose a system that can clean air from outside the engine bay.

Scoops and “Ram Air”

“Ram Air” is a marketing term that Pontiac developed in the 1960’s. Whatever their reasoning for creating such a descriptor, it is a matter of fact that the ram effect (ie compression of air resulting from its velocity) cannot be achieved at subsonic speeds. Be wary of any claims that state otherwise. Examples include the “Free Ram Air” mod, the Fast Toys Ram Air (or its equivalents from the likes of SLP, or Home Depot if you want to use your own ingenuity), and Ram Air hoods.

Putting aside all of the marketing, it is apparent that the main function of scoops is route cold air from outside the engine bay into the intake track. Cooler air is denser than warmer air, and therefore contains more oxygen in the same volume, and therefore greater horsepower potential.

A potential undesirable side effect of scoops is the potential to route relatively dirty air into the intake. This can lead to reduced air filter service intervals. In most cases, ingestion of water is typically not a legitimate concern.

Exhaust Guide


EXHAUST

There are some fairly straightforward concepts and some very complex concepts that govern exhaust system design. As a general discussion, some of the advanced topics will be omitted but the lessons will not. Again resonance and exhaust length will not be discussed. The modifications are listed in the order that they are most commonly replaced.

It is important to remember that a V6 will never sound like a V8. This is due to the frequency of cylinder firing, the number of cylinders per bank, and the bore:stroke ratio.

Mufflers

When replaced by itself, the muffler has the potential to show modest gains in power. The key word is modest. The best reason to replace only the muffler is if a different exhaust note is desired. Arguments abound over which muffler offers the best tone. However, tone is purely subjective and therefore what one person may consider the best another may consider obnoxious.

Most aftermarket mufflers utilize absorption, destructive interference or a combination in order to quiet the exhaust noise. A straight through muffler utilizing absorption will typically be the least restrictive but also provide the least sound cancellation.

A muffler should be selected that provides the most flow, while creating a tone that the user can stand to hear. It is wise to find someone with the same care and the muffler you are interested purchasing and listen to his or her vehicle. With a daily driver, you would do well to compromise in the direction of sound. All aftermarket mufflers will flow much better than the stock muffler, but not all will have a sound that appeals to you.

Resonators warrant mentioning in this section because they serve the same function as a muffler. Some vehicles come with resonators from the factory. A resonator utilizes destructive interference to reduce the exhaust noise. This is different than bullet mufflers and glass packs, which generally utilize absorptive material.

Pipes

Why do aftermarket exhaust systems increase performance? Did you say increased pipe diameter? The most common misconception about performance exhaust systems is that as pipe diameter increases, backpressure decreases and therefore the largest diameter system is the best. Erase this from your mind.

The best exhaust system is one in which you increase flow rate in terms of CFM while maintaining or increasing flow velocity. Flow velocity is key. If the system is too large in diameter, then velocity will be too low until you go high in the rev range. Scavenging at low RPM will suffer, and torque will drop. For V6 F-bodies, the most commonly recommended exhaust systems are of the 3 inch diameter variety. In contrast, three out of the four exhaust manufacturers (Magnaflow, Flowmaster, B&B) that market V6 specific cat backs manufacture them in 2.5 inch diameter.

What is the reason for the disparity? Unfortunately there are many more V8 kits available that will fit on a V6. People tried them and saw gains. That coupled with the “bigger is better” mentality “proved” that 3 inch systems were the way to go on the 3.4 and 3.8L motors. In 99% of the cases, a 2.5 inch system should offer superior performance than a 3 inch system on naturally aspirated 3.4 and 3.8L engines. In order to see advantages with 3 inch pipe, one must either rev much higher than 6000 RPMs or use some manner of forced induction.

MagnaFlow's Stance on Pipe Diameter

Flowmaster's Stance on Pipe Diameter

DynoMax's Stance on Pipe Diameter

Put pipes and a muffler in a package and you have a “cat back” exhaust system. Generally all the pipes from the catalytic converter back to the muffler and the tailpipes are included. However on the 4th Gen F-bodies, typically the S-shaped pipe after the converter is not included. This can be remedied by purchasing a section of mandrel bent U pipes or 45 degree bends and having the exhaust shop fabricate the “S-pipe.” As stated before, 2.5” exhaust is the best choice for most vehicles, but most V8 3” systems can be adapted with minor modifications.

Cut-Outs

These are a simple way in which to create a variable exhaust system. The cutout is closed for normal driving, and then can be opened when high performance is needed and little sound dampening is required. The cut out can be placed anywhere within the exhaust path, but is most effective as it is placed farther forward. Generally most prefer locating it before or after the catalytic converter. If mounted after the last O2 sensor, you should not ever have to worry about tripping a diagnostic code.

Catalytic Converters

A high flow catalytic converter has the potential to increase the flow rate of the exhaust. As with mufflers, a unit should be chosen that provides the highest flow rate. The most common aftermarket catalytic converters that are recommended include Catco (which are cheap), and Carsound / Magnaflow (which are more expensive, but higher quality).

Why not no cat or a gutted cat? Besides increased pollution, generally cars without a catalytic converter do not perform as well as ones fitted with a good aftermarket high flow converter.

The 3” inlet/outlet, 14” length universal Catco is PN 6907
The 3” inlet/outlet, 16” length universal Carsound is PN 94009, or 94039 with single O2 boss.

Unfortunately many people set a diagnostic code after installing an aftermarket cat. If this occurs, an O2 sim can be used in place of the rear O2 sensor. Casper’s Electronics makes an O2 sim that has been tailored for the 1997+ V6 F-body, PN 104046.

Headers

Headers are designed so that exhaust pulses “pull” subsequent pulses out of the cylinders. Each exhaust pulse is a pressure wave. By varying the length of the primaries, the RPM range at which this will be most effective can be determined. Typically longer tubes are best for lower RPM and shorter tubes are best at higher RPM. Usually primary diameter is dependent on valve and port size. Pacesetter, RkSport, and CIA make headers for the 3.8L F-body, and RkSport and Pacesetter make headers for the 3.4L.

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