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Secrets of Exhaust & Intake Design By Nathan Morris

www.UltimateResourceGuides.com

© Copyright 2003-2004 All Rights Reserved

Limits of Liability / Disclaimer of Warranty: The author and publisher of this book and the accompanying materials have used their best efforts in preparing this program. The author and publisher make no representation or warranties with respect to the accuracy, applicability, fitness, or completeness of the contents of this program. They disclaim any warranties (expressed or implied), merchantability, or fitness for any particular purpose. The author and publisher shall in no event be held liable for any loss or other damages, including but not limited to special, incidental, consequential, or other damages. The authors and publisher do not warrant the performance, effectiveness or applicability of any sites listed in this book. All links are for information purposes only and are not warranted for content, accuracy or any other implied or explicit purpose. This manual contains material protected under International and Federal Copyright Laws and Treaties. Any unauthorized reprint or use of this material is prohibited.

Secrets of Intake and Exhaust Design

Table of Contents Chapter 1 - Secrets of the Exhaust System Hardware of the Exhaust System ……………….Catalytic Converter(s) ……………….Resonator(s) ……………….Muffler(s) ……………….Exhaust Piping

Design Considerations ……………….Choosing an Application ……………….Materials ……………….Bend Types ……………….Pipe Size ……………….Pipe Sizing Chart Considerations by Application ……………….Street ……………….Street/Strip ……………….Pure Race

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Chapter 2 – Secrets of the Intake System Hardware of the Intake System ……………….Air Filter ……………….Intake Tube Design Considerations ……………….Short Ram vs. Cold Air Intake ……………….Determining Length and Diameter ……………….Materials ……………….Filters

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Chapter 1

Secrets of the Exhaust System In this section you will learn the basics of a generic exhaust system. You will also learn how to improve upon their inherent flaws and to squeeze every ounce of performance from your vehicle. When tampering with exhaust systems, it is very important to be aware of local laws, as in some locals it is illegal to tamper with these systems. Be sure that it is okay to modify them at all in your area, and what the requirements are. For example, in some locations it’s okay to modify anything from the catalytic converter back, so long as the resulting noise emission is less than 96 db. If this is the case in your area, you are held responsible for obtaining proper testing and so forth. Good luck and happy learning!

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Hardware of the Exhaust System Exhaust Valves Exhaust Header(s) We will not talk too much about these two below, however, they are worth mentioning as they are more or less the starting point for our journey down the exhaust tube. When combustion occurs in a chamber, the exhaust valves lift when the camshaft tells them to. When this occurs, the spent mixture from the cylinder travels out the holes created by the valves lifting and out into the exhaust manifold, or header. In 4 cylinder cars there is only one header, but in any V-style motor there will be two of these. The next few parts of the exhaust system are the main focus of this section and will involve some relatively in-depth discussion. If you are ready to learn then hold on, some of this may require reading twice or perhaps even three times.

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Catalytic Converter(s)

In order to clean up the air, the EPA passed a law stating that all new vehicles be equipped with Catalytic Converters. The “cats” job is to make sure that the poisonous gasses that are contained in raw exhaust do not make it out into the environment (or rather, your lungs), and really do a good job of doing this. The “cat” also does a great job of quieting modern cars down and making the exhaust note deeper. A lot of people will tell you that by removing this device, by replacing it with some kind of straight pipe will gain you great deals of horsepower. While it is logical to say this due to the idea that it’s a restriction, one would be wrong to make this assumption. Besides being highly illegal ($25,000 fine attached), smelling really bad, and being very loud, it will actually make very little difference. If you plan on replacing the catalytic converter, there are several companies (Referenced in appendix A) that make high flow converters that actually still perform their duties. These will gain you just as much power, if there is any to gain in the first place, and will keep you legal and safe. In closing to this section, it is very important to note that a damaged or worn catalytic converter CAN cause serious horsepower loss as well as other problems. Therefore, you should check it’s condition especially if your vehicle of choice is rather old. Sometimes a new OEM converter alone can help regain a few ponies especially on 8+ year old cars.

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Resonator(s)

Resonators come in two varieties. One is a true resonator, and the other is a glass pack-style muffler. These resonators show up in the exhaust pipe as extra “canisters”, typically between the muffler(s) and the catalytic converter(s). They do not in any way restrict flow, but of course you should match their size to the size of your pipe. Removing them will make things a lot louder and produce a higher pitch. The reason removing a resonator will make the exhaust note higher pitched, and albeit louder, is that resonators basically take the sound waves from the exhaust and force them outward towards the walls of the resonator. They then “bounce” back and meet sound waves in the center of the pipe, canceling out the sound waves. As well, glass pack style resonators also have fiberglass packing around them to help reduce some sound as well. You should invest in at least 1, if not 2 resonators for your new exhaust system, unless you are using this for an all out race car and don’t mind the noise, in which case they can be scrapped for less weight.

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Muffler(s)

This is where a lot of enthusiasts get their exhaust all wrong. First of all, no muffler can give you any horsepower. However, an aftermarket muffler can free up horsepower, being blocked by the OEM (Original Equipment) muffler. However, without doing other modifications to especially the exhaust pipe, this modification would mostly be for looks and sound. Basically, a muffler’s job is to quiet the otherwise very loud exhaust down a bit. Various mufflers do this in different ways. Absorption mufflers are the best at letting exhaust flow freely, however they are terrible at reducing noise. Old school glass pack mufflers (cherry bomb), as well as the new stainless “canister” mufflers are great examples of this type.

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Exhaust Piping

This my friends is where most of the power is picked up in most applications. Factory exhaust systems are typically undersized, and far from smoothly bent and routed. Therefore a great deal of gain can be had by replacing this economical solution with a mandrel bent exhaust that is correctly sized for your application. Many aftermarket systems combine “cat-back” piping with properly sized resonators and mufflers to create respectable horsepower gains. The only trouble with this is the price. Most of these systems go for $500 and beyond. These units also typically use stainless steel as opposed to the common cast iron of OEM systems. Stainless steel comes with two advantages: one, the systems are far more resistant to rust and two, they are far lighter weight, and less weight means less power required to reach a certain goal. These exhaust systems however, are also somewhat generic, so this book aims to help you design a very effective exhaust system for your vehicle with minimal cost.

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Design Considerations When designing your cars exhaust system, it is important to first decide realistically what the goals for your car are, and what it is used for. That is what the first section of this chapter will focus on, deciding what type of system to design. For those of you who want a pre made route, this chapter is not for you. However, if you want to get the most potential out of your car, read on to discover the secrets of designing a high quality cat back system.

Materials When choosing a material for your new exhaust system the only reason you would not use Stainless Steel is cost. While it does last a lot longer than most materials out there, and is even lighter than a lot of materials, it is very expensive relative to say, aluminized pipe. However, I personally believe that it is certainly worth the extra cost to go with the Stainless Steel. Just don’t expect it to last literally forever, as stainless steel doesn’t mean it won’t rust, it just means that it stains less than other metals. This is a “must” for anyone living the Atlantic Northeast of the United States.

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Bend Types There are two different types of bends that you will find when you go to get your pipes bent, or when you order your piping. The first type is the most common as well as the cheapest. Crush bent piping is pipe that is placed in a machine that literally bends the pipe and does not conserve the same inside diameter throughout the pipe. Therefore, this is not an ideal choice for our new exhaust system, as just like a car must be aerodynamic; a free flowing exhaust must have very few if any imperfections inside it. You should avoid crush bending like the plague. What you are looking for when getting your new piping is what is known as mandrel bent pipe. Basically what mandrel bent pipe is, is pipe that is bent on a special machine that maintains the pipes inside diameter throughout a bend. What results is an unrestricted, nice, smooth bend. Ask the shop doing your work, or the company you are ordering from if they can mandrel bend piping for you. Mandrel bent pipes are said to flow 35% more than a crimp bend. Looking below you can see why crimped pipes flow worse than mandrel bent pipes.

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Pipe Size

When designing an exhaust system, the size of the piping is perhaps the most important detail. Many tuners really hurt their potential a lot in this area, and therefore this section hopes to clear up some myths and set things straight on exhaust pipe size. The problem with choosing the right size is that it can not be determined from some simple formula, as there are way too many factors involves. Things such as bends, type of bends, resonators, cats, and so on are all involved in making it difficult to simply make some mathematical equation to solve the trouble. However, we run into a difficulty with exhaust pipe size as if it is too large, atmospheric pressure can travel into the pipe and actually hold exhaust gasses in longer. This obviously is very bad, and this is the reason that bigger is certainly not always better. If the pipe is too small as with OEM piping, the exhaust pressure has a hard time exiting the motor. Therefore we must arrive at a general set of rules, and the following chart is the best guideline that is available. It will get you within a tenth or two of the maximum power that you could get given a certain design. You can’t get much better than just to go by this table. One consideration when choosing a single exhaust versus a dual exhaust, is that especially in smaller engines, a single exhaust is going to be much lighter weight than a dual exhaust and is therefore the most beneficial to performance. Even if the duals flow slightly better, the weight will offset any minute gain in that case. In large V8s, and some V6s, duals may be a desirable thing.

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Pipe Sizing Chart Displacement

Horsepower

Single Exhaust

Dual Exhaust

1.5L-2.0L

100

2.00” (50.8mm)

2.00” (50.8mm)

150

2.25” (57.15mm)

2.00” (50.8mm)

200

2.50” (63.5mm)

2.00” (50.8mm)

150

2.25” (57.15mm)

2.00” (50.8mm)

200

2.50” (63.5mm)

2.00” (50.8mm)

250

2.50” (63.5mm)

2.25” (57.15mm)

200

2.50” (63.5mm)

2.00” (50.8mm)

250

2.50” (63.5mm)

2.25” (57.15mm)

300

3.00” (76.2mm)

2.50” (63.5mm)

250

3.00” (76.2mm)

2.25” (57.15mm)

300

3.00” (76.2mm)

2.25” (57.15mm)

350

3.50” (88.9mm)

2.50” (63.5mm)

300

3.00” (76.2mm)

2.50” (63.5mm)

350

3.50” (88.9mm)

2.50” (63.5mm)

400

4.00” (101.6mm)

3.00” (76.2mm)

350

3.50” (88.9mm)

2.50” (63.5mm)

400

4.00” (101.6mm)

3.00” (76.2mm)

450

4.00” (101.6mm)

3.00” (76.2mm)

2.0L-2.5L

2.5L-3.0L

3.0L-3.5L

3.5L-4.0L

4.0L-4.5L

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Choosing an Application As I mentioned in the previous paragraph, it is important that we first decide on the type of cat back system we wish to create. We will divide the systems up into three categories, one which we will refer to as Pure Race, Street/Strip, and Street. I will do my best to cover design principals for each type of system.

Street The street application are basically for people who want a little extra performance from their car, but do not want the noise at the expense of a small amount of performance. Truthfully, this is basically the stealthier version of a street/strip exhaust. The basic idea with a Street style exhaust is to maintain stock bends, but to replace the piping with stainless steel mandrel bent pipe. This will not only add life to the exhaust system, but will also save us some weight. The next consideration is that we will want to remain completely street legal, so a catalytic converter must remain in tact. We will however, preferably replace the stock unit with a high-flow unit from a respectable manufacturer. Remember that it’s important that the catalytic converter meets the standards for the laws in your area. This along with the piping will give a little extra sound from the exhaust, but should not make it unbearable. Since we would like to keep things on the quiet side, we will also install a set of resonators in the pipe. These should be two resonators at least 20” in length each, this will not interfere with flow, the only down side is the added 5 or so pounds. You may opt for one longer resonator. Finally, we will round the system out with a good flowing muffler. Now, there are a few good mufflers out there that would make a good choice. Some are cheaper solutions than others. For example, for a lot of Hondas, the muffler(s) off of an S2000 or other high performance Honda would work beautifully. Basically this is a budget idea, that involves finding the muffler of a “higher performance” vehicle in the junk yard. If this is not an option, or you’re opting for new parts, several manufacturers make mufflers that are “straight through”, but are very well Page 14 © 2004 Ultimate Resource Guides

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insulated for minimal sound. One that I’m particularly a fan of is the Wide Open Performance muffler from Magnaflow (magnaflow.com).

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Street/Strip A Street/Strip exhaust is intended for individuals who would like to get more performance on their daily driver, but would also like for their exhaust to be suitable for drag racing on the weekends. Obviously, this means putting up with a little more noise, and perhaps breaking a few rules. First of all, let me say that even at this level of performance, I highly recommend using a high flow catalytic converter. Not only because of the legal aspects, but it really is just simply silly to straight pipe the catalytic converter on a street/race application. Not only is it extremely loud, but it’ll also make your car sound raspier and well, you probably won’t like it. Anyhow, at this level we’ll call it an optional device. Next stop, the resonators, I highly recommend one 21” or longer resonator. This is done not only to maintain the sanity of the driver, but also to avoid (especially in 4 cylinder models) that annoying high pitched sound that comes with a very open exhaust. Again, you lose no performance through this, only about 5lbs or so of extra weight. With mufflers, you have a little more freedom on a street-strip design. Preferably, you want a straight-through muffler that is either a canister style or an oval muffler (quieter due to more packing). Remember that the larger the tip on the muffler, the louder it will be, so be careful when choosing mufflers.

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Pure Race A Pure Race exhaust is one that makes no exceptions for noise, or for practicality. There is also a great deal of freedom here. We will assume however that you do want to occasionally drive this car on the roads. Remembering of course that you’re taking a risk especially in areas where getting tickets for loud exhausts (CA) or worse (not cat), and I highly recommend against this practice. First of all, go ahead and scrap the catalytic converter as well as the resonators. These are useless weight and we no longer care about the sound of the car. Use a light-weight stainless steel canister style muffler, or other light weight muffler. The muffler is mostly for sanity driving the vehicle. As you design this exhaust system, take every step possible to ensure that the exhaust pipe has as few bends as possible. This may take some creativity on your behalf, however, by decreasing the number of bends in the pipe you help improve the smoothness of the exhaust pulse traveling through the pipe.

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Chapter 2 Secrets of the Intake System In this section, we will cover the various components of the Intake System in most vehicles. As well, we will cover how to choose the best components for a custom intake system, and the math involved in doing that. As well, as we journey down this path of information we will uncover the truth behind all the hype with intake systems on the market these days. You’ll understand when to use a cold air intake and when to use a short ram intake, as cold air intakes are not always the best route to take.

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Hardware of the Intake System While there are certainly more components to the overall intake system of any fuel injected vehicle, I will only focus on two specific ones for simplicity sake. These are the two elements that are particularly important to us when designing our own intake.

Air Filter The air filter is what sits between your engine and the dust and other debris in the air. Without it, I’m sure you guessed, the engine would ingest all kinds of gunk that would eventually or perhaps even suddenly lead to damage to your engine. However, not all air filters were created equally by any means. In fact there are several different types of air filters out there on the market and while all technically perform the same task, some do this better than others. Most important to us, some of them flow better than others. We will discuss this topic a little more a little later.

Intake Tube When you open the hood of just about any car, finding the intake tube and air filter is usually a trivial exercise, simply a matter of locating the really ugly black square box and the ugly black tube that runs from it into the motor. While that is a crude description at best, it certainly is the case in most modern cars. As with many other items on modern cars, these intake tubes are not only designed to be quiet but also to be extremely cheap to produce. Therefore, they are also inherently very poor at transferring air quickly, smoothly, and well, there is just a great deal that we can improve upon.

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Short Ram vs. Cold Air Intake It has long been a battle of which is better, a Short Ram or a Cold Air Intake? Many cling to the advertising hype that colder air is denser air and therefore a cold air intake is always going to be the best bet. While I agree that colder air is certainly denser, and that this is an important topic, there is a great deal more to the process of cramming as much air into the engine as possible. Cold Air Intakes have a great advantage over short ram intakes in many applications. The reason being is that they relocate the air filter outside the hot engine bay where the filter can suck up very cool air by comparison. While this is certainly a huge advantage, if we can somehow isolate the air filter of a short ram intake in some kind of heat shielded box the cold air intake now has no real advantage. Okay, I can tell that I’m probably losing quite a few people right now. But that is okay, and I’m sure we’ll get things straightened out in just a few lines. Now, once we remove the air temperature issue, the single most important thing (other than smoothness and number of bends), is the length and what section of the power band you need to be enhancing the most. This is where we run into an interesting point. The higher the engine revs, the shorter the intake arm should be. The lower the engine revs in comparison, the longer you will probably want the intake arm to be. The reason being, is that the rule of thumb with intake runners and intake arms is that the longer the pipe, the more low end power. This is why on a car like the Honda S2000 that revs over 9000 rpm you will notice very short intake runners. Whereas, on a truck or some other vehicle intended for low rev driving, will have very long intake runners, and probably a very long intake arm as well.

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Determining Length and Diameter

So how do we determine how long or how short? The general rule is to start with 6000 RPM as your target RPM, and say 13 inches is the perfect length for that target RPM. For every 1000 RPM higher, subtract 1.3 inches and for every 1000 RPM lower, add 1.3 inches. The next complicated question is to determine just how big the intake tube should be. That is, what the inside diameter should be. The best way to calculate this, is to take the inside diameter of the throttle body of the car, find the cross sectional area of the throttle body, add 25% more, and solve for the diameter. To simply what I just said, take a 60mm throttle body (inside diameter measurement), divide by two to get the radius. The cross sectional area of our throttle body is simply Pi*(30^2), or 2826 sq mm. Now, multiply 2826 by 1.25 to get an area 25% larger. 3532.5 is what we get after doing this calculation. Now, to solve for the diameter of our intake tube, divide 3532.5 by Pi (3.14 as our estimate). We get 1125, and now we take the square root of that 33.54 mm. Multiply this number by 2 because that is just the radius, and we get 67.08 mm. Therefore, our intake tube should be 67.08mm in inside diameter. 1 inch is 25.4 mm, so therefore our intake tube should be 2.64inches in diameter. While this is a very odd size, you can round up or down, depending upon what you deem most appropriate for your situation. The intake tube should be slightly larger than the throttle body itself, for your reference.

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Materials The next big question on everyone’s mind is what material to use. Aluminum seems to be the big choice of most manufactures. Not only is it relatively lightweight, but it also fails to retain heat as well as some other metals. If you choose to use Aluminum, make sure you coat it with some kind of hightemp ceramic based paint. You can find this readily at your local auto parts store, or Wal-Mart. This will help to further prevent heat from soaking into the intake pipe. Another idea is to use plastic. While this is much more difficult for the average person, it is certainly the ultimate solution. Not only is it lightweight, but it will not really absorb any heat. PVC should not be used for those of you thinking about it, and likely you will be stuck with aluminum unless you have the facilities to work with plastic.

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Filters The next thing that we need to discuss is the other part of our intake, the filter. There are a few different types of filters out there. There are panel and conic filters, and then there are gauze/mesh, paper, and foam filters. I’ll begin with the differences between panel and conic filters. Panel filters, are typically what we know as “stock air filters”. They are typically flat, and are literally just a flat panel with filter material in the center. These filters flow terribly. The reason they flow poorly is that they lack surface area. If you remember high school geometry, it takes a much larger rectangle to cover the same amount of surface area as a cone. How much more flow does a conic filter have over a panel filter? Roughly double, a typical paper panel filter flows 320 cfm on a specific car, and on the same car, a conic paper filter flows 550 cfm. Therefore, in our efforts to increase air flow, we will be using a conic air filter to achieve maximum results. Now that we’ve cleared up which shape of filter to use, we will tackle the topic of what material to use. In order to qualify as an air filter for a specific car, manufacturers must meet a “minimal filtering level”. What this means is that no matter what the filter is made of, it is required that it filter out a certain amount of particles. Paper filters, in order to meet this requirement need to be extra thick or have highly compressed particles. This by design automatically disqualifies paper in the race for flowing highly. Next comes a debatable topic. That is the topic of foam versus gauze/mesh filters. HKS and GReddy are two companies that have in the past used foam element filters for better flow quality. However, K&N one of the most respected manufacturers of filters insists that not only do their filters flow better, but that they also filter better. In my own experiments, I found K&N’s argument to be more grounded. While both filters seemingly flowed at approximately the same rate, the foam filter element not only slowly lost it’s ability to flow as high as the K&N style filter, but it also failed to filter as well. My slightly less than scientific experiment however has been backed up by many very scientific studies done by various magazines throughout the year. A gauze style filter will flow at 6.03 cfm of air per square inch whereas a paper element ill flow at around 4.95 cfm. Therefore, it is my recommendation that a K&N (gauge/mesh style) filter be used for your new intake. The added bonus is that K&N filters are reusable, and Page 23 © 2004 Ultimate Resource Guides

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you’ll never have to replace it. The “recharge” kit for a K&N style filter is about $9 at the time of this writing, and will certainly last you the life of your car.

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Choosing a Filter Size

In general, you want to fit the largest available filter. However, below is a calculation to determine the minimum sized filter. Obviously, you want it as big as what can fit under your hood, and no smaller than the area calculated with the calculation below. Area = CID x RPM -------------20839

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Appendix A www.flowmastermufflers.com www.magnaflow.com www.carsound.com www.randomtechnology.com www.kandnfilters.com

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