F150online Forums - THE Exhaust Guide

Some of you may have noticed some of the same threads getting posted over and over again. So it's time to finally make the holy bible of exhaust write-up to try and cut down on the repetitive topics. If I miss any main points or topics, be sure to tell me. I want to make this as complete as possible.

1. Exhaust Configurations

There are three types of exhaust configurations that are available for the F150 series. These include Single In/Single Out (SISO), Single In/Dual Out (SIDO), and true duals. I'm going to cover all these setups and throw in some pro's/con's to help people make an informed decision.

SISO's

A SISO configuration is the most basic setup that is available for the F150 series of trucks. All this setup is, is a Y-pipe exiting to a single intermediate pipe, then entering into a muffler with a single inlet, exiting the muffler through a single exit, and leaving the entire exhaust system by a single tailpipe.

I know this is kind of confusing, but hop underneath your completely stock truck, and the OEM exhaust system is a prime example of a SISO exhaust configuration.

Attachment 33060

There are several pro's and con's associated with SISO configurations. This includes:
+ Being cheap
+ Offering exceptional towing performance
+ Keeping that stock-ish look

- Tone and volume can only go so far
- Lack of overall aggressiveness
- Not offering very good performance at the higher RPM range

Pipe sizes play a somewhat large part for the SISO configuration. On the 97-08 F150's, the exhaust pipe diameter goes from 2.5" from the manifolds, to a 2.5" intermediate pipe, and exiting to a 2.5" tailpipe. Not the world’s greatest for any performance, especially with the extremely restrictive stock Y-pipe, but that's for later.

The optimal pipe size for a custom SISO exhaust is 3" from the Y-pipe, all the way to the back (minus the tip). This will provide the best sound quality and performance for towing.

SIDO's

SIDO configurations are definitely the most popular aftermarket setups for the F150 series truck. 9.5 times out of 10, if you look under an F150 with dual tips, it's going to be a SIDO. That's not a bad or good thing, but just a fun fact I guess.

Basically, a SIDO is the same as a SISO, except gases exit the muffler through dual outlets and leaves the entire system through dual tailpipes. The simplicity is one of the main reasons why most members opt for them.

Attachment 33061

Some of the pro's and con's consist of:
+ Look like true duals
+ Good sound quality
+ Relatively inexpensive

- Have the same limitations at higher RPM's as SISO's

Optimal pipes sizes are similar to SISO's except muffler outlets and tailpipes should be 2.5". This will maintain good low end torque for towing and cruising around town.

True Duals

Now we get to the next level of configs for these trucks. These are usually reserved for members who want the best of the best in terms of performance and sound quality. These are also the most complicated and expensive configs for these trucks.

The idea for true duals is to have one pipe for one side of the engine. It gets more complicated than that on our asymmetrical layouts, but that will be covered later on.

The piping starts from the manifolds and goes all the back with 2 separate pipes. The trade off is that one pipe will be longer than the other because more bends are required to run along side the other pipe. The fuel tank on the driver side prevents the left pipe from being routed through, so both pipes must go through the passenger side and split off past the axle (depending on the desired exits).

Attachment 33062

Pro's and con's include:
+ Superior tone, aggressiveness, and volume
+ Good performance down low and up top (depending on cross over and pipe size)

- Expensive
- Complicated
- Lot's of pieces

Pipe size is different on true duals. There are 2 main diameters that members use. 2.25" for low end torque, and 2.5" for top end power. Sound quality also changes ever so slightly with the 2 sizes, the bigger being slightly deeper. Other than that, you can't tell a difference in the pipe size by just listening.

I should also mention that too small a pipe size can run the risk of choking the engine, hindering performance. Going too big also hurts performance. So keep it at either 2.25", or 2.5".

Cross Overs

Now we move into cross overs. On an asymmetrical true dual exhaust system a REAL true dual exhaust is one of the least recommended configs to run. The reason being that one side of the engine has to work harder to move the same amount of gas out of the system, hurting performance. Scavenging doesn't happen either, also going to be covered later.

The 2 cross over choices for true duals is the H-pipe and the X-pipe. For SISO's and SIDO's, the only choice is the Y-pipe.

The H-pipe

The H-pipe is the simplest, and cheapest cross over for the true dual configs. All that's needed is 2 holes cut out of each pipe and a connecting pipe welded up to those holes. It's simple and straight to the point. Scavenging does occur with an H-pipe, but it's not nearly as effective as an X-pipe, but it's a hell of a lot better than REAL true duals.

H-pipes on a symmetric exhaust helps promote good top end power because most of the exhaust gases are pushed passed the actual cross over pipe, making for a smooth exit. But this certainly is not the case on an asymmetric system. One side of the system still has a longer journey to make than the other, making that side of the engine have to work harder than the other.

Attachment 33063

The X-pipe

The X-pipe is the pinnacle of crossovers. They offer the best overall performance on a true dual config. X-pipes perform the best because of how both streams of exhaust gasses are forced into each other. This increases scavenging which increases power and torque.

Sound-wise, many top members prefer X-pipes due to the smoothness. X-pipes have a less choppy sound compared to REAL true duals and H-pipes.

Attachment 33064

The Scavenging Effect

Now we can discuss this almighty scavenging effect that many refer to and believe in devoutly.

Quote:

When an engine starts its exhaust stroke, the piston moves up the cylinder bore, decreasing the total chamber volume. When the exhaust valve opens, the high pressure exhaust gas escapes into the exhaust manifold or header, creating an exhaust pulse comprising three main parts: The high-pressure head is created by the large pressure difference between the exhaust in the combustion chamber and the atmospheric pressure outside of the exhaust system. As the exhaust gases equalize between the combustion chamber and the atmosphere, the difference in pressure decreases and the exhaust velocity decreases. This forms the medium-pressure body component of the exhaust pulse. The remaining exhaust gas forms the low-pressure tail component. This tail component may initially match ambient atmospheric pressure, but the momentum of the high- and medium- pressure components reduces the pressure in the combustion chamber to a lower-than-atmospheric level. This relatively low pressure helps to extract all the combustion products from the cylinder and induct the intake charge during the overlap period when both intake and exhaust valves are partially open. The effect is known as scavenging. Length, cross-sectional area, and shaping of the exhaust ports and pipeworks influences the degree of scavenging effect, and the engine speed range over which scavenging occurs.
The magnitude of the exhaust scavenging effect is a direct function of the velocity of the high and medium pressure components of the exhaust pulse. Performance headers work to increase the exhaust velocity as much as possible. One technique is tuned-length primary tubes. This technique attempts to time the occurrence of each exhaust pulse, to occur one after the other in succession while still in the exhaust system. The lower pressure tail of an exhaust pulse then serves to create a greater pressure difference between the high pressure head of the next exhaust pulse, thus increasing the velocity of that exhaust pulse. In V6 and V8 engines where there is more than one exhaust bank, Y-pipes and X-pipes work on the same principle of using the low pressure component of an exhaust pulse to increase the velocity of the next exhaust pulse.
Great care must be used when selecting the length and diameter of the primary tubes. Tubes that are too large will cause the exhaust gas to expand and slow down, decreasing the scavenging effect. Tubes that are too small will create exhaust flow resistance which the engine must work to expel the exhaust gas from the chamber, reducing power and leaving exhaust in the chamber to dilute the incoming intake charge. Since engines produce more exhaust gas at higher speeds, the header(s) are tuned to a particular engine speed range according to the intended application. Typically, wide primary tubes offer the best gains in power and torque at higher engine speeds, while narrow tubes offer the best gains at lower speeds.
Many headers are also resonance tuned, to utilize the low-pressure reflected wave rarefaction pulse which can help scavenging the combustion chamber during valve overlap. This pulse is created in all exhaust systems each time a change in density occurs, such as when exhaust merges into the collector. For clarification, the rarefaction pulse is the technical term for the same process that was described above in the "head, body, tail" description. By tuning the length of the primary tubes, usually by means of resonance tuning, the rarefaction pulse can be timed to coincide with the exact moment valve overlap occurs. Typically, long primary tubes resonate at a lower engine speed than short primary tubes.
Some modern exhaust headers are available with a ceramic coating. This coating serves to prohibit rust and to reduce the amount of heat radiated into the engine bay. The heat reduction will help prevent intake manifold heat soak, which will decrease the temperature of the air entering the engine.

TL: DR

Exhaust gasses passing through on one side of the engine pull gasses out of the other side to lessen the load on the engine, making more power.

The Myth of Back-Pressure

Most members who have dared to post in the exhaust section and use the “back-pressure” term have been rightly ridiculed shunned. The reason this is, because back-pressure is a complete myth and an utter farce.

Quote:

One thing that I get tired of hearing is the concept that engines need back-pressure. Simply, there is no properly tuned engine where increasing exhaust back-pressure causes an improvement - in power, torque or fuel economy. One of the reasons that this idea has gained support is because when people change their exhaust they seldom check the air/fuel ratio or re-map the ignition timing to once again give optimal performance. For example, some MAP sensed cars drop substantially in power with a large exhaust fitted because they are then running lean.

Atmospherically inducted cars that use a tuned length system to improve cylinder scavenging (via extractors, for example) are sensitive to exhaust diameters within the tuned length part of the system. This means that the maximum effect of exhaust pulsing may come from an exhaust system that is small enough that some exhaust back-pressure is developed. However, that is a quite different concept to saying that engines "need" exhaust back-pressure! Turbocharged engines require as big an exhaust as possible, with the same applying for naturally aspirated cars once the tuned length part of the exhaust is passed.

Few tests have been done that clearly show the affect of changing back-pressure. Most muffler and exhaust comparison tests change more than one parameter simultaneously, making the identification of exhaust back-pressure as a culprit difficult. However, Wollongong (Australia) mechanic Kevin Davis is one who has done very extensive testing of varying back-pressure on a number of performance engines. These range from turbocharged Subaru Liberty [Legacy] RS flat fours to full-house traditional pushrod V8's. In not one case has he found any improvement in any engine performance parameter by increasing exhaust back-pressure!

The tests came about because Kevin has developed a patented variable flow exhaust that uses a butterfly within the exhaust pipe. He initially expected to use the system to cause some back-pressure at low loads "to help torque". However, he soon changed his mind when any increase in back-pressure proved to decrease torque (and therefore power at those revs) on a properly tuned engine! What increasing the back-pressure does do is dramatically quieten the exhaust.

One of the engine dyno tests carried out by Kevin was on warm 351 4V Cleveland V8. Following the extractors, he fitted a huge exhaust that gave a measured zero back-pressure. Torque peaked at 423 ft-lb at 4700 rpm, with power a rousing 441hp at 6300 rpm. He then dialled-in 1.5 psi back-pressure. Note that very few exhausts are capable of delivering such a low back-pressure on a road car. Even with this small amount of back-pressure, peak torque dropped by 4 per cent and peak power by 5 per cent. He then changed the butterfly position to give 2.5 psi back-pressure. Torque and power decreased again, both dropping by 7 per cent over having zero back-pressure!

And if you still believe that exhaust back-pressure improves performance, simply block off part of your exhaust outlet and see if your car goes any faster!

2. Muffler Types

There are three different types of mufflers in this field, baffled, chambered, and flow-through (aka straight-through). All three will be broken down explained further.

Baffled Mufflers

Many OEM mufflers are baffled. Baffled mufflers work by forcing exhaust gases through an inlet, down a louvered tube, into an expansion chamber, and eventually through an offset outlet pipe. Baffled mufflers are the worst performing mufflers out of all three. Exhaust gasses are obstructed from quickly passing from the actual muffler at every turn.

Sound-wise, not many prefer the sound of a baffled muffler due to the odd sound note and overly raspy tone.

Attachment 33065

Chambered Mufflers

Many companies produce chambered mufflers, they are best recognized as Flowmaster and Thrush. The design of chambered mufflers is similar to baffled mufflers, except that chambered mufflers use plates to amplify and resonate the ever-so recognizable tone. Chambered mufflers are only slightly better than baffled mufflers in terms of performance. The exiting gasses are still obstructed in several areas due to the plates that are used to generate the sound and tone.

Many members prefer the sound and note of chambered mufflers. They are best described as a “metallicy” sound. They offer a cheap and effective method to making an exhaust loud and aggressive in the lower RPM ranges, while drastically reducing their sound in the higher RPM’s. Most chambered mufflers have the same base note with only volume increases in other models

Attachment 33066

Flow-Through (Straight-Through) Mufflers

Flow-through mufflers are the best performing mufflers of the three. The reason being is that in most cases, one can look from one end of the muffler and see straight through (get it?) to the other end of the muffler. This allows exhaust gasses to exit the system faster and lets the engine make power instead of using it to force obstructed exhaust gasses out.

Many members prefer straight-through mufflers because of the aggressive sound/or deep mellow tone that they offer, depending on the brand and model chosen. Drone is also reduced in straight-through mufflers (depending on the model chosen) compared to chambered mufflers.

Attachment 33067

3. Cats and Catless

Cats, or catalytic converters, are one of the great inventions to come out of the green era (sarcasm). What a cat is exactly, is an element (usually platinum) that heats up and reduces one harmful gas to a less harmful gas. This section will cover three areas of cats: OEM cats and their configurations, hi-flow cats, and no cats.

OEM Cats

OEM cats on the F150 series have changed from the 1997-2011 range. 1997-2005 trucks have a 4 cat system that includes a pair of small cats, called pre-cats, and a pair of large cats down stream that handle the majority of gas conversion. The main goal of pre-cats is to act like a resonator, canceling out unwanted engine and exhaust noise (mostly catered to the elderly and the feminine :lol:). Trucks with a 4 cat setup are in general extremely quiet. Many users opt to remove the rear "fat" cats and only use the pre-cat, which sounds quite similar to hi-flow cats. Some members with 97-03 trucks have had issues with CEL's popping up soon after the removal of the rear cats has been accomplished, but can easily be corrected with a custom tuned programmer or "fooling" the computer with an O2 sensor mod.

The 2 cat system came around halfway through 2005, and every truck after that point has only had the one pair of cats. The 2 cats are just 2 large cats that handle all of the gas conversion and some sound cancellation. Trucks with the 2 cat system tend to still be extremely quiet, but slightly louder than the 4 cat trucks. Nothing can be done to these cats besides removing them all together, or replacing them with a good set of hi-flow cats.

Attachment 33068

Hi-Flow Cats

One of the greatest mod one can do for their exhaust. Hi-flow cats drastically increase sound quality, volume, and overall aggressiveness of any exhaust. They do this while still complying with emission tests. Hi-flow cats accomplish this by being much shorter than OEM cats, but still having enough of the catalyst material inside to fulfill its job. Depending on the engine size dictates which cats should be used on a given vehicle. Most cats have it specified that they are to be use only on vehicles with equal to less than XX.XX liters or cubic inches.

Many members who have invested a great deal of money and time into their exhaust opt for hi-flow cats. The most widely used cats on the F150 series is the Magnaflow 94106 cats.

Attachment 33069

No Cats

Going back to the days when cats were first mandated on all US vehicles, people were taking them off. Today is still the same, but not quite as common as it once was. Going catless greatly increases the sound quality, volume, and overall aggressiveness of an exhaust system while also being extremely cheap depending on how you go about it. There are some problems that one may face while running a catless system on a vehicle that comes from the factory with a set on.

A CEL can come on, and usually does, because the O2 sensors pick up on the exhaust gasses being too rich and try to lean out the A/F mixture. This also reduces performance because engine is setting itself out of its ideal parameters to try and correct the issue. This can easily be corrected with the help of a custom tuned programmer, by using the O2 sensor mod, or by installing O2 eliminators.

Even if a CEL has been turned off by means of a programmer, O2 sensor mod, or eliminators, it will not pass a "sniffer test" that many emission shops use. So if you live in a town that requires strict emission testing, going catless is not a good option.

Another possible issue with a catless system is that if police officers are especially strict on cat mods, they will be able to smell you out. Even by just driving by, they can easily smell the "illegalness" of your vehicle.

4. Tips and Exits

Tips

The tips are the most visible part of the exhaust system. They come in many shapes and styles ranging from the classic slash cut, to the rolled tips, to stacks (in extreme and ridiculed situations). There are many more styles and shapes, but I'm not going to go into those. Tips act as an amplifier because they are usually larger than the pipe diameter. Think of tips as a megaphone or a bullhorn. They amplify your voice in the same way. The bigger and longer the tip, the louder and deeper your exhaust will sound, very simple. Tips are largely for aesthetics, so pick one, or a pair, that look good to you.

There are many different materials that are used in making tips today. The most common being polished stainless steel and chrome over regular steel. It's difficult to tell the difference in the two unless you are up very close and can inspect them. Chrome over steel tips tend to be shinier and have much more luster than polished stainless tips, but the trade-off is durability and longevity. Chrome over steel tips will rust from the inside going out after a relatively short amount of time. Stainless steel tips take a much longer time to start rusting, and can be refurbished with some steel wool and polishing chemicals. Stainless tips do cost more than chrome tips, but they should be opted for if you plan on owning your truck for more than 2 years.

Tips do not affect performance as long as they are the same size as the pipe or bigger, and do not obstruct the flow of the gasses. If you like the way a certain tip looks and are afraid of it negatively affecting your performance, have no fear.

Exit Locations

Exit locations also greatly affect the overall sound and volume of the exhaust. They also affect your performance depending on which one you opt for. The most known exit types are straight-out-the-backs, 45's, 90's, dumps, and Lightning style. I will go over all of these and cover how each changes the sound of the exhaust and if it affects the performance.

- Straight-Out-The-Back

The straight-out-the-back (SOTB) configuration is the most widely used and recognizable exit known to man. It looks good and projects the sound out quite well. SOTB exits look sporty and look good on most if not all vehicles.

There are some downsides to this config. One is that if you tow a trailer, the sound can be projected directly at the trailer and in turn be reflected back at the cab. This can make thing a little unpleasant depending on your exhaust specs and you endurance to drone. (I personally wish I could tow something all the time so I can get that great sound directed back at me :lol:)

Another downside is that if you go off-roading a lot in some hostile territory, you run the risk of crushing a tip between the ground and your bumper. I don't know if this is a common problem or not, but I thought it would be good advise to think twice if you are planning to go SOTB and also do some hardcore O/R'ing.

Attachment 33070

- 45's

Another great looking tip exit that caters more towards the 4WD and lifted trucks. They have that certain aggressive yet sporty look that can only be pulled off when done properly. The sound projection of the 45's is probably the best out of them all. They project them backwards and off to the sides, making tunnel drives extremely enjoyable. Heavy off-roaders should look into a 45 exit because the is almost no chance of damaging a tip due to rough terrain. Sound redirection from towing is still noticeable with 45's, but not nearly as bad as SOTB's.

One of the problems that comes with the territory is that 45'd tips tend to get dirtier much quicker than SOTB's because they are right there next to the tires getting hit by mud/dirt/rocks/you name it. If you go this route, be prepared to clean up those tips often.

Attachment 33071

- 90's

The 90 degree config is a somewhat rare thing to see nowadays, but some members have it and love it. The 90's have all of the positives as the 45's with only one of the same negatives. They project the sound out to the sides of the vehicle making any trip through a narrow street or through a tunnel very enjoyable. They also do not project the sound towards a trailer if towing, so no redirected noise.

Dirty tips are still a problem because they are right in the way of debris coming off of the tires.

http://i6.photobucket.com/albums/y23...50fella90s.jpg

- Lightning Style

The Lightning style is one of the more unique exits. Possibly one of the sportiest looking and most aggressive sounding exit that you can get on a truck. The reason that this exit is the most aggressive is because the entire exhaust system is shortened and everything is closer to each other so that those tips can exit right in front of the rear passenger side tire. Even though the outside sound quality is superb, there are quite a few negatives that go along with it.

Drone is really bad on trucks that has a Lightning style exit. Because the muffler(s) and tips are under the cab, making a good portion of the sound generated directly under your ass.

Sound projection is a bit awkward with Lightning exits. The tips themselves are only on the right side of the truck, meaning that all the sound is sent out to that side. So people on the left side don't get that life altering experience that the right sider's do.

Tips getting dirty is a problem with the Lightning exit, just as the 45's and 90's.

Attachment 33072

- Dumps

Dumps are a bit of a gray area when it comes to us exhaust fanatics. In most cases, dumps do not have any tips and project all of the sound from the exhaust straight down. This tends to increase drone and decrease outside sound because there are no tips to amplify and project the sound. Many opt for dumps because it gives their truck a "cleaner" look. There are a few different types of dumps, over the axle dumps, under cab dumps, and dumps with tips. OTA dumps tend to have less drone, UC dumps tend to be louder outside and have a large amount of drone, and dumps with tips end up having the best sound quality of all three.

Drone and interior noise is increased with a dumped exhaust of any kind, while the outside noise is reduced. This is because in most cases, there are no tips and they are pointed straight down towards the ground.

One good point is that there are no tips to keep clean.

Attachment 33073

5. Pipe Material and Bends

There are a few materials that are widely accepted as being usable materials for exhaust pipes. The two main materials includes stainless steel and aluminized steel. Both will be discussed with pro's and con's listed.

-Aluminized Steel Pipes

Aluminized pipes were once highly used by many auto manufactures in their OEM equipment. They have now been phased out for the better quality of stainless pipes, mostly for their durability and lack of rust that accumulates on them.

Aluminized pipes are the lowest quality between the two, mainly because they do not resist corrosion nearly as well as stainless pipes. One should take their location into heavy consideration when deciding between the two. If one live in a northern climate where salt is regulary spread out on the roads every winter, then aluminized pipes are not recommended.

There are positives for aluminized steel pipes. Some of those include the price. Aluminzed pipes are relatively cheap compared to stainless steel pipes. Availability is also a positive. Exhaust shops are not guaranteed to have stainless pipes in stock, but always have aluminized pipes in stock.

-Stainless Steel Pipes

Stainless steel pipes have been the most desirable because of its corrosion resistence and ability to still look new after years of use. That also depends on its grade. They come in 409 and 304, 409 being of inferior quality to 304.

409 stainless will become rusty in around a year or less, but it will not rust through the pipe like not-stainless pipes will. They can still last for 10+ years without having any problems other than surface rust. If you live up north, 409 is a much better material than aluminized pipes, when can rust out in just a few years. The upside to 409 stainless is the price. It is still more expensive than aluminzed pipes, but less so than 304 stainless. It is still somewhat rare for an exhaust shop to carry stainless steel pipes, but accomodations can be made if you are willing to pay.

304 stainless is considered the best exhaust pipe material you can have. It has the highest chromium level which equals a better corrosion resistence level. Even after several years, 304 pipes can still look brand new. One would not have to worry about rust with these pipes if they were so inclined to pay for them. The downside to 304 stainless is the price. Since 304 is of the best quality, they cost the most. It is rare for an exhaust shop to have 304 in stock, but it is quite expensive when they do.