The exhaust thread

[Willravel]

(This is a great article from www.overboost.com)

We've seen too much misinformation regarding exhaust theory. What kind of misinformation? For starters, there are a lot of people in the "Bigger is Better" camp. We're talking about exhaust pipe diameters. Even the big magazine editors are boldly smattering statements like, "For a turbo car, you can't get an exhaust pipe that's too big." Also, terms like "back pressure" and the statement, "An engine needs back pressure to run properly!" really rub us the wrong way.


Let's start from the beginning. What is an exhaust system? Silly question? Not hardly. Exhaust systems carry out several functions. Among them are: (1) Getting hot, noxious exhaust gasses from your engine to a place away from the engine compartment; (2) Significantly attenuating noise output from the engine; and (3) In the case of modern cars, reduce exhaust emissions.


Hardware


In order to give you a really good idea of what makes up an exhaust system, let's start with what exhaust gas travels through to get out of your car, as well as some terms and definitions:

After your air/fuel mixture (or nitrous/fuel mixture) burns, you will obviously have some leftovers consisting of a few unburned hydrocarbons (fuel), carbon monoxide, carbon dioxide, nitrogen oxides, sulfur dioxide, phosphorus, and the occasional molecule of a heavy metal, such as lead or molybdenum. These are all in gaseous form, and will be under a lot of pressure as the piston rushes them out of the cylinder and into the exhaust manifold or header. They will also be hotter 'n Hades. (After all, this was the explosion of an air/fuel mixture, right?) An exhaust manifold is usually made of cast iron, and its' primary purpose is to funnel several exhaust ports into one, so you don't need four exhaust pipes sticking out the back of your Civic.

Exhaust manifolds are usually pretty restrictive to the flow of exhaust gas, and thus waste a lot of power because your pistons have to push on the exhaust gasses pretty hard to get them out. So why does virtually every new automobile sold have exhaust manifolds? Because they are cheap to produce, and easy to install. Real cheap. Real easy. Like me.

"Ok," you ask, "so now what?" Ah, good thing you asked. The performance alternative to the exhaust manifold is a header. What's the difference? Where a manifold usually has several holes converging into a common chamber to route all your gasses, a header has precisely formed tubes that curve gently to join your exhaust ports to your exhaust pipe. How does this help? First of all, as with any fluid, exhaust gasses must be treated gently for maximum horsepower production. You don't want to just slam-bang exhaust gas from your engine into the exhaust system. No way, Jo-se'! Just as the body of your '94 Eclipse is beautiful, swoopy, and aerodynamic, so must be the inside of your exhaust system.

Secondly, a header can be "tuned" to slightly alter your engines' characteristics. We'll go in-depth into header tuning a little later.

Nextly, exhaust gasses exit from your manifold or header, travel through a bit of pipe, then end up in the catalytic converter, or "cat". The cat's main job is to help clean up some of the harmful chemicals from your exhaust gas so they don't end up in your lungs. In most cars, they also do a great job of quieting things down and giving any exhaust system a deeper, mellow tone. You'll see a lot of Self-Proclaimed Master Technicians (SPMT's) telling people that removing a cat will get you tons of power. There's room for debate on this, but in our experience, removing a catalytic converter from a new car won't gain you much in the horsepower department. It can also get you a $1500 fine if the EPA finds out! If you drive an OBD-II equipped car, you'll also get that damn annoying CHECK ENGINE light burnin' up your dashboard. (And for all you racers concerned with OBD-II's fabled "limp mode", you can put your fears to rest.)

From the catalytic converter, the exhaust gasses go through a bit more pipe and then into a muffler, or system consisting of several mufflers and/or resonators.


Are you a muff?


Exhaust gases leave the engine under extremely high pressure. If we allowed exhaust gasses escape to the atmosphere directly from the exhaust port, you can well imagine how loud and cop-attracting the noise would be. For the same reason gunshots are loud, engine exhaust is loud. Sure, it might be cool to drive around on the street with that testosterone producing, chest-thumping, 150 decibel roar coming from your car… for about 5.3 seconds. (Not 5.2 or 5.4 seconds… 5.3.) Even the gentleman's gentleman has gotta use a muffler, or system of mufflers, on their exhaust.

Again, you may hear a few SPMT's tell you that "Borla mufflers make horsepower!" Or "An engine needs some backpressure to run properly!" Nonsense. A muffler can no more "make" horsepower than Wile E. Coyote can catch roadrunners. Any technician with any dyno experience will tell you that the best mufflers are no mufflers at all!


Types of Muff


Mufflers can take care of the silencing chores by three major methods: Absorption, Restriction, and Reflection. Mufflers can use one method, or all three, to attenuate sound that is not so pleasing to the ears of the Highway Patrol.

The absorption method is probably the least effective at quelling engine roar, but the benefit is that "absorbers" are also best at letting exhaust gas through. Good examples of absorbers are the mufflers found in GReddy BL-series exhausts, DynoMax UltraFlow, and the good old-fashioned Cherry Bomb glasspack.

Absorption mufflers are also the simplest. All of the above named mufflers utilize a simple construction consisting of a perforated tube that goes through a can filled with a packing material, such as fiberglass or steel wool. This is similar to simply punching holes in your exhaust pipe, then wrapping it up with insulation. Neat, huh?

Another trick absorption mufflers use to kill off noise is, well, tricky. For example, the Hooker Aero Chamber muffler is a straight-through design, with a catch. Instead of a simple, perforated tube, there is a chamber inside the muffler that is much larger than the rest of the exhaust pipe. This design abates sound more efficiently than your standard straight-through because when the exhaust gasses enter this large chamber they slow down dramatically. This gives them more time to dwell in the sound insulation, and thus absorb more noise. The large chamber gently tapers back into the smaller size of your exhaust pipe, and the exhaust gasses are sent on their merry way to the tailpipe.


Restriction


Doesn't that word just make your skin crawl? It's right up there in the same league with words like "maim" and "rape".

Obviously, a restrictive muffler doesn't require much engineering expertise, and is almost always the least expensive to manufacture. Thus, we find restrictive mufflers on almost all OEM exhaust systems. We won't waste much time on the restrictive muffler except to say that if you got 'em, you might not want to flaunt 'em.


Reflection


Probably the most sophisticated type of muffler is the reflector. They often utilize absorption principles in conjunction with reflection to make the ultimate high-performance silencer. Remember any of your junior high school math? Specifically, that like numbers cancel each other when on a criss-cross? That's the same principal used by the reflective muffler. Sound is a wave. And when two like waves collide, they will "cancel" each other and leave nothing to call a corpse but a spot of low-grade heat.

There are numerous engineering tricks used in the reflective muffler. Hedman Hedders makes a muffler that looks a lot like a glasspack. In fact, it is a glasspack with a catch. The outer casing is sized just-so, so that high-pitched engine sound (what we deem "noise") is reflected back into the core of the muffler… where those sound waves meet their maker as they slam right into a torrent of more sound waves of like wavelength coming straight from the engine. And, this muffler is packed with a lot of fiberglass to help absorb any straggling noise that might be lagging behind.


The Exhaust Pulse


To gain a more complete understanding of how mufflers and headers do their job, we must be familiar with the dynamics of the exhaust pulse itself. Exhaust gas does not come out of the engine in one continuous stream. Since exhaust valves open and close, exhaust gas will flow, then stop, and then flow again as the exhaust valve opens. The more cylinders you have, the closer together these pulses run.

Keep in mind that for a "pulse" to move, the leading edge must be of a higher pressure than the surrounding atmosphere. The "body" of a pulse is very close to ambient pressure, and the tail end of the pulse is lower than ambient. It is so low, in fact, that it is almost a complete vacuum! The pressure differential is what keeps a pulse moving. A good Mr. Wizard experiment to illustrate this is a coffee can with the metal ends cut out and replaced with the plastic lids. Cut a hole in one of the lids, point it toward a lit candle and thump on the other plastic lid. What happens? The candle flame jumps, then blows out! The "jump" is caused by the high-pressure bow of the pulse we just created, and the candle goes out because the trailing portion of the pulse doesn't have enough oxygen-containing air to support combustion. Neat, huh?

Ok, now that we know that exhaust gas is actually a series of pulses, we can use this knowledge to propagate the forward-motion to the tailpipe. How? Ah, more of the engineering tricks we are so fond of come in to play here.

Just as Paula Abdul will tell you that opposites attract, the low pressure tail end of an exhaust pulse will most definitely attract the high-pressure bow of the following pulse, effectively "sucking" it along. This is what's so cool about a header. The runners on a header are specifically tuned to allow our exhaust pulses to "line up" and "suck" each other along! Whoa, bet you didn't know that! This brings up a few more issues, since engines rev at various speeds, the exhaust pulses don't always exactly line up. Thus, the reason for the Try-Y header, a 4-into-1 header, etc. Most Honda headers are tuned to make the most horsepower in high RPM ranges; usually 4,500 to 6,500 RPM. A good 4-into-1 header, such as the ones sold by Gude, are optimal for that high winding horsepower you've always dreamed of. What are exhaust manifolds and stock exhaust systems good for? Besides a really cheap boat anchor? If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! Something to keep in mind, though, is that even though an OEM exhaust may make gobs of low-end torque, they are not the most efficient setup overall, since your engine has to work so hard to expel those exhaust gasses. Also, a header does a pretty good job of additionally "sucking" more exhaust from your combustion chamber, so on the next intake stroke there's lots more fresh air to burn. Think of it this way: At 8,000 RPM, your Integra GS-R is making 280 pulses per second. There's a lot more to be gained by minimizing pumping losses as this busy time than optimizing torque production during the slow season.


General Rules of Thumb with Headers


You will undoubtedly see a variety of headers at your local speed shop. While you won't be able to determine the optimal power range of the headers by eyeballing them, you'll find that in general, the best high-revving horsepower can be had with headers utilizing larger diameter, shorter primary tubes. Headers with smaller, longer primaries will get you
slightly better fuel economy and better street driveability. With four cylinder engines, these are also usually of the Tri-Y design, such as the DC Sports and Lightspeed headers.


Do Mufflers "Make" Horsepower?


The answer, simply, is no. The most efficient mufflers can only employ the same scavenging effect as a header, to help slightly overcome the loss of efficiency introduced into the system as back pressure. But I have yet to see an engine that made more power with a muffler than an open header exhaust. "So," you ask, "what the hell is the best flowing muffler I can buy?"

According to the flowbench, two of the best flowing units you can buy are the Walker Dyno Max and the Cyclone Sonic. They even slightly out flow the straight through designs from HKS and GReddy BL series. Amongst the worst, are the Thrush Turbo and Flow Master mufflers. We'll flow some of the newer mufflers as they become available at our local Chief auto.


Resonators


On your typical cat-back exhaust system, you'll see a couple of bulges in the piping that are apparently mini-mufflers out to help the big muffler that hangs out back. These are called Helmholtz Resonators and are very similar to glasspacks. The main difference is that firstly, there is no sound-absorbing fiberglass or steel wool in a Resonator. And secondly, their main method of silencing is the reflective principle, not absorption. An easy way to tell the difference between a glasspack and a true Helmholtz Resonator is to "ping" one with your finger. A glasspack will make a dull thud, and a true Resonator will make a clear "ping!" sound.


Turbos


Another object that might be sitting in your exhaust flow is a turbine from a turbocharger. If that is the case, we envy you.

Not only that, but turbos introduce a bit of backpressure to your exhaust system, thus making it a bit quieter. All of the typical scavenging rules still apply, but with a twist. Mufflers work really well now! Remember, one of the silencing methods is restriction, and a turbine is just that, a restriction.

This is actually where the term "turbo muffler" is coined. Since a turbine does a pretty good job of silencing, OEM turbo mufflers can do a lot less restricting to quiet things down. Of course, aftermarket manufacturers took advantage of this performance image and branded a lot of their products with the "turbo" name in order to drum up more business from the high performance crowd. We're sad to say that the term "turbo" has been bastardized in this respect, and would like that to serve as a warning. A "turbo" muffler is not necessarily a high-performance muffler.


Pipe Sizing


We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.

Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. For engines making 250 to 350 horsepower, the generally accepted pipe diameter is 3 to 3 ½ inches. Over that amount, you'd be best off going to 4 inches. If you have an engine making over 400 to 500 horsepower, you'd better be happy capping off the fun with a 4 inch exhaust. Ah, the drawbacks of horsepower. The best alternative here would probably be to just run open
exhaust!*


Other Rules


A lot of the time, you'll hear someone talking about how much hotter the exhaust system on a turbo car gets than a naturally aspirated car. Well, if you are catching my drift so far, you'll know that this is a bunch of BS. The temperature of exhaust gas is controlled by air/fuel mixture, spark, and cam timing. Not the turbo hanging off the exhaust manifold.

When designing an exhaust system, turbocharged engines follow the same rules as naturally aspirated engines. About the only difference is that the turbo engine will require quite a bit less silencing.

Another thing to keep in mind is that, even though it would be really super cool to get a 4 inch, mandrel bent exhaust system installed under your car, keep in mind that all of that beautiful art work won't do you a bit of good if the piping is so big that it gets punctured as you drag it over a speed bump! A good example of this is the 3 inch, cat back system sold by Thermal Research and Development for the Talon/Laser/Eclipse cars. The piping is too big to follow the stock routing exactly, and instead of going up over the rear suspension control arms, it hangs down below the mechanicals, right there in reach of large rocks! So when designing your Ultimate Exhaust System, do be careful!

[GetRdone]

"The piping is too big to follow the stock routing exactly, and instead of going up over the rear suspension control arms, it hangs down below the mechanicals, right there in reach of large rocks!"

What the hell are they doing driving an eagle talon over large rocks?

[Willravel]

Oh you're missing out if you haven't taken a talon off-roading. [EDIT: I was kidding]
The real problems you might face are overzelous speedbumps and steep driveways. You need at least some ground clearance.

[GetRdone]

ive seen lots of rally x / dirt track racing with dsm's. The thing is all those cars didnt have any exhausts, so rocks dont matter. I dont see when people would take a performance street car off road.....cept the time my dad decided to take my celica (not really a performace car) into some logging road and slide it aroudn till he lost all me hubcaps.

[Rippley]

I think the point is that the "large rocks" comment was stating a fact by exaggeration, not suggesting that offroading Talons is something a lot of people do...

[Willravel]

Hahahahaha! Very good post, Rippley. I was trying to explain that an exhaust that sits too low is more likely to run into problems. Many cars and trucks that have exhaust modifications can have suspension modifications, making the automobile closer to the ground. The combination of the auto being closer to the ground and the larger exhaust makes it more likely to bump ro scratch it on the ground when going over large bumps or rougher terrain. Speed bumps, pot holes, overzealous driveways, etc. can all caouse problems.

[catback]

A lot of the time, you'll hear someone talking about how much hotter the exhaust system on a turbo car gets than a naturally aspirated car. Well, if you are catching my drift so far, you'll know that this is a bunch of BS. The temperature of exhaust gas is controlled by air/fuel mixture, spark, and cam timing. Not the turbo hanging off the exhaust manifold.

Where do you get your information cuse that's all wrong, the high rpms of the turbo itself generates heat as does the added backpressure. A free-flowing exhaust is cooler because heat doesn't build up it dissipates with a turbo in place the exhaust doesn't flow as freely as stock and heat doesn't dissipate as fast with the turbo in the way.

[Nimisys]

Originally Posted by catback

Where do you get your information cuse that's all wrong, the high rpms of the turbo itself generates heat as does the added backpressure. A free-flowing exhaust is cooler because heat doesn't build up it dissipates with a turbo in place the exhaust doesn't flow as freely as stock and heat doesn't dissipate as fast with the turbo in the way.

in comparison with the temperature of the exhast gasses flowing through it, the heat contrabution of the turbo bearings is negilable. it is enough that it needs to be controlled for the bearings lifespan, however the amount of heat it generates in comparison is not worth worring about. the turbo needs pressure to operate, and since the volume is fixed, the temperature goes up as a result. worth noting however would be the difference in pressure between the exhast manifold tot eh turbo and the downpipe out of the turbo.

[Willravel]

Originally Posted by catback

Where do you get your information cuse that's all wrong, the high rpms of the turbo itself generates heat as does the added backpressure. A free-flowing exhaust is cooler because heat doesn't build up it dissipates with a turbo in place the exhaust doesn't flow as freely as stock and heat doesn't dissipate as fast with the turbo in the way.

Whoa, slow down. I cited the article at the beginning, so the answer to your question is "I got the information from overboost.com. This is not just some kid posting what he heard from a bud in second period history in highschool. Overboost.com is a respected source of information, auto articles, and parts." It's not wrong.

[Rippley]

Originally Posted by willravel

Hahahahaha! Very good post, Rippley. I was trying to explain that an exhaust that sits too low is more likely to run into problems. Many cars and trucks that have exhaust modifications can have suspension modifications, making the automobile closer to the ground. The combination of the auto being closer to the ground and the larger exhaust makes it more likely to bump ro scratch it on the ground when going over large bumps or rougher terrain. Speed bumps, pot holes, overzealous driveways, etc. can all caouse problems.

Thank for noticing, willravel. I drive a dropped car, and am forever having to watch out for "terrain", even in the city.
It seemed to me that the thread was taking a turn for the worse, so I thought I'd try and head it off at the pass... seems like it worked...

[albazeroex]

Originally Posted by willravel

Another object that might be sitting in your exhaust flow is a turbine from a turbocharger. If that is the case, we envy you.

yes and i envy my friend's integra

[Ilow]

Originally Posted by catback

Where do you get your information cuse that's all wrong, the high rpms of the turbo itself generates heat as does the added backpressure. A free-flowing exhaust is cooler because heat doesn't build up it dissipates with a turbo in place the exhaust doesn't flow as freely as stock and heat doesn't dissipate as fast with the turbo in the way.

I have to disagree with this. First, the turbo does not generate much excess heat due to most turbos having water and/or oil jackets to cool them, and second, the gas is heated when it exits the turbo due to the friction created by the air being compressed, but then it is usually cooled by an intercooler before it enters the intake. It is possible that because of the air/fuel mix that Willravel refers to is being increased due to the turbo compressing the air the exhaust might be a little hotter, but I think that the overall effect of a turbo on exhaust heat is negligible.
edit: I appreciate the info, Will, but am curious as to what prompted this explosion of information.

[herostar]

Originally Posted by willravel

(This is a great article from www.overboost.com)
Another thing to keep in mind is that, even though it would be really super cool to get a 4 inch, mandrel bent exhaust system installed under your car, keep in mind that all of that beautiful art work won't do you a bit of good if the piping is so big that it gets punctured as you drag it over a speed bump! A good example of this is the 3 inch, cat back system sold by Thermal Research and Development for the Talon/Laser/Eclipse cars. The piping is too big to follow the stock routing exactly, and instead of going up over the rear suspension control arms, it hangs down below the mechanicals, right there in reach of large rocks! So when designing your Ultimate Exhaust System, do be careful!

I have that exhaust, no problems with it being too low...

Very informative article. I think everyone who works at an exhaust shop should read it. Then I'd never hear of that god damned "backpressure is good" nonsense again.

[herostar]

Originally Posted by catback

Where do you get your information cause that's all wrong, the high rpms of the turbo itself generates heat as does the added backpressure. A free-flowing exhaust is cooler because heat doesn't build up it dissipates with a turbo in place the exhaust doesn't flow as freely as stock and heat doesn't dissipate as fast with the turbo in the way.

That's why you get a bigger turbo :wink:

I know that on my 95 Eclipse with a 2.4L stroker motor and a 60-1 turbo my exhaust gas temperature at 7000 rpm on a WOT run gets up to about 1500 degrees at my probe, which is about 5" from the head. On my friend's N/A honda his probe in the same spot gets to about 1200 degrees in the same conditions.

[catback]

Originally Posted by Ilow

I have to disagree with this. First, the turbo does not generate much excess heat due to most turbos having water and/or oil jackets to cool them, and second, the gas is heated when it exits the turbo due to the friction created by the air being compressed, but then it is usually cooled by an intercooler before it enters the intake. It is possible that because of the air/fuel mix that Willravel refers to is being increased due to the turbo compressing the air the exhaust might be a little hotter, but I think that the overall effect of a turbo on exhaust heat is negligible.
edit: I appreciate the info, Will, but am curious as to what prompted this explosion of information.

Good info but wrong side of the turbo although oil does cool the turbo.

That's why you get a bigger turbo :wink: I know that on my 95 Eclipse with a 2.4L stroker motor and a 60-1 turbo my exhaust gas temperature at 7000 rpm on a WOT run gets up to about 1500 degrees at my probe, which is about 5" from the head. On my friend's N/A honda his probe in the same spot gets to about 1200 degrees in the same conditions.

You've seen the proof and it's irrefutable regardless of what ever overboost may say (can't always believe what you read). I stand by my statement added backpressure leads to added EGT (Exhaust Gas Temp) and a turbo adds backpressure and some heat of it's own otherwise no one would sell EGT gauges to people with turbos. The other thing wrong is the statement "Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter." It's wrong because it's done by engineers, exhaust fabricators, and some car buffs all the time. There are formulas, just because overboost or anyone else doesn't know them or bother to use them doesn't mean they don't exist.

Just because it ends in .com doesn't make it any more reliable a source than hear-say.

[Willravel]

Originally Posted by Ilow

I have to disagree with this. First, the turbo does not generate much excess heat due to most turbos having water and/or oil jackets to cool them, and second, the gas is heated when it exits the turbo due to the friction created by the air being compressed, but then it is usually cooled by an intercooler before it enters the intake. It is possible that because of the air/fuel mix that Willravel refers to is being increased due to the turbo compressing the air the exhaust might be a little hotter, but I think that the overall effect of a turbo on exhaust heat is negligible.
edit: I appreciate the info, Will, but am curious as to what prompted this explosion of information.

Well, I've been writing articles for about 2 years now. I figured I'd write some for TFP about a month and a half back (see "men: you should read this" thread in sexuality about the menstrual cycle, "Willravel's: The Sex You Deserve", etc). I figured it was time to branch out a bit. I love cars, so I figured I branch out here. About 1/5 of the post you see above is from the article in overboost, but I didn't want to have to cite sources on the damned thing.

BTW, I still stand by what I said about turbo heat. While the temperature may change slightly, it's not nearly enough to make any mechanical changes around it. Overboost is a great source, but it is not by a long shot my only source. One of my good friends is a prof. at Sequoia Institute (see http://www.sequoiainstitute.com/), and his opinon is the same as mine on this. I may have only modified 4 or 5 cars in my time with turbos, but I'm still 97% sure this is right.

Thanks for posting!

[kurty[B]]

The previous owner of my 4Runner thought it would be cool to put to straight-back 2 and 1/4 inch pipes out the back. While the awful loud rumble was fun for a while you could feel the lack of low-end torque from the oversized exhaust. I crushed the dual pipes off-roading, and then took it to a shop for a single 2 and 1/2 inch pipe tucked behind a wheel well (so I won't crush it off-roading), and not only does it sound great (nice rumble, but not windows shaking loud), but I can feel a massive difference in low end torque. I definitely suggest people look into the type of engine they have and at their WHOLE exhaust system, and not just the muffler.

I used to have a Rabbit GTi, and had to replace the manifold with nice headers, and gained around 7-9 hp, because the old manifolds were so restrictive. Man, I miss that little beast.

[GetRdone]

is your 4runner with the 6cyl (i think they made one didnt they?) or the 22re 4cyl? I ask because the dual exhaust really should not have negatively affected the trunk much, if at all. If its the 4cyl, than i understand how dual pipes can be a lil bit overkill.

[kurty[B]]

It is a 6 cyl. The dual was a bit much, and the person who put it on ran it directly under the support for the toe-hitch. So, off-roading this summer, just completely crushed the mufflers when I bottomed out the rear end.

Unfortunately the 3.0 6cyl in the thing does not create enough power to justify a dual exhaust. It may work on the newer 3.4 engines, but I also prefer the sound of the large single pipe to the extremely loud rumble of the duals which set off car alarms left and right (if I was still in high school I would get a kick out of that, but there's not need anymore).

[catback]

Originally Posted by willravel

Well, I've been writing articles for about 2 years now. I figured I'd write some for TFP about a month and a half back (see "men: you should read this" thread in sexuality about the menstrual cycle, "Willravel's: The Sex You Deserve", etc). I figured it was time to branch out a bit. I love cars, so I figured I branch out here. About 1/5 of the post you see above is from the article in overboost, but I didn't want to have to cite sources on the damned thing.

BTW, I still stand by what I said about turbo heat. While the temperature may change slightly, it's not nearly enough to make any mechanical changes around it. Overboost is a great source, but it is not by a long shot my only source. One of my good friends is a prof. at Sequoia Institute (see http://www.sequoiainstitute.com/), and his opinon is the same as mine on this. I may have only modified 4 or 5 cars in my time with turbos, but I'm still 97% sure this is right.

Thanks for posting!

You stand by your statement and I'll stand by mine. The term "slightly" is relative, from herostar's example of 1200 to 1500 degrees, a 300 degree increase may be a slight increase to one person but a 25% increase in temp to another. To view it in another light, a 25% increase in horsepower is a pretty nice increase (25 extra HP for every 100 horses)

[kaiho]

I'm reading this book by Stephen King, and it mentions this car having a glass (might have been fiberglass) exhaust system. Is this possible?

[pinoychink790]

i don't know. fiberglass can't withstand too much heat. but then again. ahh this is going to bug me

[JusticeForPhat]

For anyone interested in the design aspects of intakes and exhausts I highly reccomend this book and the others by the same authors.


As far as the turbo / backpressure / EGT debate goes, I'll give my $.02. The turbo itself doesnt increase backpressure or EGT's that much, its the fact that your generally ramming an assload more air into an engine, advancing spark a shitload, and running at higher rpms. Those are all things that contribute to higher EGT's. Wanna see your EGT take a dive? Richen the mixture up a c-hair and increase the distance between injector and port. The excess fuel wont burn as hot, and you will lose some power. Changing the port distance will give more time for fuel and air to mix and in the process cool down the intake charge.

Really want to end the debate? Someone pony up the $2k for a decent pressure transducer. The last time I set up a full DAQ system on an engine dyno those were a little bit out of the price range. We did however measure the pressure drop and temp difference across the intercooler along with a bunch of other stuff.

For the hell of it here is the intercooler data.


The idea was to apply load to the engine for 10 seconds, give it a ten second break and repeat. Easier said than done considering the water valve on the dyno takes like 40 turns to open.

[Willravel]

Glass melts between 2500-2900ºF. It bends at lower temperatres. It also cracks with extreme temperature changes (like driving for a while - hot exhaust - and driving through a puddle). I'd say no for glass.

I'll check on fiberglass.

[GetRdone]

maybe they meant a Glasspack, u know one of those loud things people put before the muffler, or instead of the muffler.

[PDOUBLEOP]

How about some advice...My 93 chevy k2500 has a 350 in it. Someone put a smaller muffler and single tail pipe(I'm assuming from a 305) on it. I know this engine is not a powerhouse but it really feels soft and the mpg isn't very good. I'm thinking that I need to pull that muffler and single tail pipe and put on something that will breathe a little better. I'm assuming it came with a 3" exhaust with dual tails from the factory.

[Powderedmaggot]

My exhaust goes through one of 2 manifolds into one of 2 turbochargers then out one of 2 4" straight pipe stacks just behind he cab. My diesel flies.