We are onto the exhaust system. So as usual, this first
episode is a general overview and then in subsequent videos,
we'll dive into the details, all the various components. (upbeat music) You maybe noticed what
we've done is we've skipped from the air intake system, straight into the exhaust system. And we've gone past the
fuel injection system and the ignition system. And there's a reason for that. There's logic in the madness. The reason is that the
sensors on the exhaust system, really the critical sensors that determine the fuel injection process, how much fuel is injected into the engine. So we need to fit the exhaust and we need to talk about those sensors before we can go back and talk about the actual combustion process that generates these exhaust gasses. So, what does the exhaust actually do? Well fairly obviously, it
brings the combustion gasses, those waste gasses from
the combustion process away from the engine out to an exit point, generally at the rear of
the vehicle, the tailpipe. Now why do we need the
move those gasses anyway? Well they're toxic, they're
hot and they're corrosive. So we want to get them away from occupants and also away from any
sensitive mechanicals. We don't want them blowing
around in the engine compartment. So the exhaust system
brings those gasses away and out of the vehicle to the atmosphere. But along that journey from
point A, being the engine, and point B being the tailpipe, from A to B we also do some work. So the exhaust needs to
do a few different tasks. One of those tasks is to modify the noise of the exhaust, it also reduces emissions and it should, hopefully,
enhance the performance of the engine. So we'll look at how it
does those three things, as we go along and talk about
these various components. Now let's see what the exhaust
system actually consists of. We've got on the engine side,
we have a heat shield here. And this heat shield protects
the air cleaner box here, which is made of plastic, from the heat of the exhaust system. So let's remove that air filter box so we can actually see what's happening. This is our heat shield
which protects the air box. Just pop that off. You can see underneath, we
have the exhaust headers. So the exhaust gasses come
out of the cylinder head here, through these exhaust
ports into the headers. So at this point, as the
gasses come out there, they're at about 800 degrees Celsius, which is about 1500 Fahrenheit. They make their way along
this pipe as they come along, they cool down. So once we hit the
catalytic converter here, those gasses, once this
system's up to temperature, they can be about 450 Celsius, about 800 Fahrenheit as
we come further along. By the time we get to the tailpipe here those gasses are probably coming out about a hundred Celsius, 210
Fahrenheit, something like that. So we have a steady cooling of the gasses as they come along this system. But at this end they're piping hot so we need the heat shield. (upbeat music) This is our manifold or our exhaust header and the function of this
is just to gather together the gasses that come from each cylinder. So we've got four
cylinders on this engine, we have four pipes, these
are called primaries that come off the exhaust ports. And you can see that these join together, so these two cylinders are joined here. This is a collector and
they join into one pipe and make their way down and
then those two pipes join into one pipe which makes its way to the rear of the vehicle. Now the length of these primaries, the distance of these
collectors from the head, and the fact that we have
four pipes going into two, and then two pipes going into one, all of those design factors
play a role in the performance of the engine. Now that's something
that we'll look at later. But it's important to
know that the placement of these collectors and
the diameters of the pipes and the lengths of these
pipes, does have an impact on the performance of the vehicle. From there, we move down. So what do we have on the header here? Okay, we have a component
on this side of the header which is the EGR pipe. So we have a small pipe that runs off the exhaust manifold, the header here, and along around the
back of the engine here, back to the air intake,
back to the intake manifold. And we saw the other end
of that when we talked about the intake manifold,
we saw the valve, the EGR valve that controls the flow of gasses along this pipe. Essentially, the EGR system
takes some of the exhaust gas and puts it into the intake system, mixes it with the intake gasses to reduce the combustion temperature
inside the engine. We'll talk about that in its
own video on EGR systems. And the main reason for the EGR system, is to cut down on the
amount of nitrogen oxide in the emissions from the vehicle. (upbeat music) So as we come down the manifold here, we come to the first
of our oxygen sensors. So on every exhaust system,
on every modern vehicle, there will be at least one, probably two or more oxygen sensors. They're also called O2
sensors or lambda sensors. They're all three names
for the same thing. So on this vehicle, this
front oxygen sensor, the first one that we come
to, along the exhaust system is critical in controlling
the fuel injection system. So this sensor detects
the amount of oxygen in the exhaust gasses inside the exhaust, sends that information
to the ECU, or the PCM and the computer uses that information to determine how much fuel
is injected into the engine. Very, very critical sensor. (upbeat music) Next, as we come down our
pipe, off the manifold, we come to the catalytic
converter, or the cat. Now this is the most expensive
part of the exhaust system. It contains precious metals
like platinum, palladium, mixed in with some ceramics in there that form the catalyst
for a chemical reaction, hence the name catalytic converter. So what the cat does is
it takes nasty pollutants in the exhaust gasses and converts them into less harmful gasses. So it takes nitrogen oxides, hydrocarbons, which are basically unburnt fuel and oil and carbon monoxide and
it converts those nasties into nitrogen, water and carbon dioxide, three much less harmful,
if in fact not harmful at all really, gasses which then improve the emissions of the vehicle. So the thing with the cat is it only works at high temperature, it only
works above about 400 Celsius, 750 Fahrenheit. So it needs to be towards
the hot end of the exhaust, as close to the manifold as possible. Because this thing
doesn't work until it gets up to 400 Celsius. We want it to warm up and start working as soon as possible. From the cat we hit our
second, our rear oxygen sensor. So on this vehicle we've got
two, the front one controls the fuel injection
system, and this rear one, which is an identical component, albeit with a slightly
different tail on it, this one measures the amount of oxygen at this point in the exhaust
and compares it to the first, or the computer compares it to that first front oxygen sensor. And the amount of oxygen
should have changed because the catalytic converter has used that oxygen in its processes. So this oxygen sensor
really has the function of making sure that the cat is working. If this oxygen sensor
produces an identical reading, to the front oxygen sensor,
then the ECU's gonna see that and it's gonna turn on
the Check Engine light, probably flash it to say
that the catalytic converter is not working. And it's a requirement,
it's a legal requirement for emissions on all modern vehicles. Various different setups of
these oxygen sensors exist on vehicles, so don't be
surprised if there's only one, or in fact maybe there's
five on your vehicle. Just know that they all perform more or less the same function as in reading the amount of oxygen
inside the exhaust system. (upbeat music) From this rear oxygen sensor,
we come along the pipe and we hit the first of our
two mufflers or silencers on this exhaust system. So the purpose of these mufflers is to shape and generally to
reduce the amount of noise coming off the vehicle
produced by the exhaust. And in that subject, a
very tight regulations, there's very specific
rules on how much noise an engine, a vehicle, an
exhaust system can produce and so the silencers here
have the task of bringing the noise level down. If you've ever heard an exhaust
without a silencer on it, you'll know it's incredibly loud. It's immediately apparent
if there's no muffler, no silencer on an exhaust. So they not only reduce the noise, but they also shape it. So manufacturers know that the sound of an exhaust sells vehicles. It sounds good. And particularly on this
vehicle, Mazda, with the MX5, starting with the Mk1, they knew that a good
sporty sounding exhaust would give this car more of a sporty feel, make it more of an enjoyable
driving experience, particularly when you've got
the top down on a cabriolet, you're more connected with the
exhaust sound of the vehicle. So Mazda made an effort. This is more of a resonator, it shapes the exhaust note as it works its way through the system,
whereas this rear silencer here has the meat of the silencing task in it. It's obviously much
bigger and it has a more of an absorption, more
of an effect on reducing the noise of the exhaust system. We'll talk about both of
these silencers later. We'll chop them open and see
actually what's inside them and how they work. (upbeat music) Now, coming off this rear silencer, we have the tailpipe. And the tailpipe just really has the job of taking the exhaust gasses
from the final silencer out to the rear of the vehicle to vent out to the atmosphere. And something to note is
the tip of our tailpipe here has a nice, kind of
chrome stainless effect, it's quite a stylish, polished finish. Because really, you know,
that's the only part of the exhaust system
that you actually see when you look at the vehicle. And of course as you see this chrome pipe, it gives the impression that
the rest of the exhaust system is actually a beautiful,
polished chrome, stainless steel, when in fact, most
exhaust systems are made from a mild steel with a little
bit of galvanizing on them. All exhaust system are
of a sectional design, which means they're made
up in chunks or parts. So on this system, we have
the header coming down and we have the front
pipe, which might be called the down pipe, that comes along. We have the mid pipe. We have rear pipe there. And they're bolted together
by exhaust flanges. So each section has a flange
and those are bolted together to join the system. In between the joints is a gasket. So there's different types of gasket, shaped around the actual flange itself. But on this particular joint here, we have a kind of pressed gasket here, a sheet metal type design
that fits into there and on these other, later
joints, we have a round, circular gasket which is made of a kind of heat resistant material
which is compressed when the sections are bolted together. In terms of fitting an
exhaust to a vehicle, not only does it come in
this sectional design, but it needs to be isolated from the bodywork of the vehicle. So when we talked about the engine mount, we discussed that the engine vibrates, creates a lot of vibration, which we don't want to transfer into the rest of the vehicle. So the engine is mounted on rubber blocks and the exhaust is bolted directly, it's a rigid fitting to the engine. So if the exhaust was then bolted directly to the bodywork of the
car, you would have made the engine mounts completely pointless. We would've made them totally ineffective by joining the engine
through a rigid exhaust to the bodywork. So exhaust systems will tend
to hang on rubber hangers. We've got some at the rear here. They hang on these rubber mounts which isolate the
exhaust from the bodywork and stop the vibration from the engine being carried into the
actual vehicle itself. Now there's different types. Every manufacturer has a different type of rubber exhaust mount. I don't know why they can't standardize on one particular design
but every manufacturer has a different exhaust mount design. Let's talk about the
design of exhaust systems for a second. So when a manufacturer
designs an exhaust system, there's some constraints on that design. One of those constraints is fitment. So the exhaust header, particularly, needs to fit and be
packaged into an engine bay, it needs to route around various obstacles and make its way to the
rear of the vehicle. So fitment is a key constraint. Another constraint is noise. So the exhaust system needs to achieve a certain level of noise reduction. A third element is cost,
so the manufacturer needs to build an exhaust
system at a certain cost of manufacturing and fitting that system. We also have emissions, so
the exhaust system needs to achieve certain emissions requirements and finally, we have performance. So the performance of the exhaust system, it dictates its design to a certain level. Now obviously different vehicles
place different priority on those constraints. You know, certain vehicles will
have a very strong emphasis on fitment, for example,
or noise reduction, whereas other vehicles,
perhaps performance vehicles will make more efforts to achieve
performance from a system. But the exhaust system, and in fact those different design requirements mean that an exhaust system
is one area of a vehicle where a performance part can make quite a significant
difference to the performance of the engine. Now we gonna talk about header design and the effect of what's
called scavenging, which is the way the exhaust
gasses are pulled through the engine, it increases airflow
and volumetric efficiency. We'll talk about all of that
when we discuss the header. But just know that the
trade-offs between those designs, affect the design and the
performance of an exhaust system. One of the most noticeable
things in looking at an exhaust, is the diameter of the pipes. So the diameter of a main exhaust pipe, is determined by the flow
of air through the engine at peak revs. So the cubic feet per
minute is the measure that's used for this. We measure the amount of gas
coming out of this engine, in cubic feet per minute at its peak and then the rest of the
exhaust system is sized around that requirement. So a general rule of thumb
is that for every horsepower, there's two cubic feet per minute coming out in terms of exhaust gasses. So this engine generates
108 brake-horsepower, stock engine, stock 1.6. So this will produce about
220 cubic feet per minute of exhaust gasses and those
need to be carried away along the pipe. So this is a classic, you know, your standard size of exhaust
pipe on a road vehicle is two and a quarter inches. So if we measure this pipe,
let's take a look here at the diameter of this pipe, we got 55 millimeters which is about two and a quarter inches, so this is just your classic exhaust pipe. Now on a V8 engine, you would find that you would have, you've
obviously got a larger, a larger amount of exhaust
gas being brought out, you'll probably still find
two and a quarter inch pipe on there as a stock fit. But you would find that
you got dual exhausts. So one exhaust coming off one side and another exhaust coming off
the other bank of cylinders. And those then make their
way to the rear of the car so you've effectively
got two exhaust systems on a V-shaped engine. So it can be tempting to think
that a bigger exhaust pipe is going to increase the
performance of the vehicle. It's going to move the
exhaust gasses quicker to the rear of the vehicle. And that's actually not true. So what you find is if you
have a pipe which is too big, then the velocity, the speed
of the exhaust gasses flowing along that pipe, slows down and if you have a pipe
that's too small, obviously, that restricts the flow. But it's important that there
is an optimum size of pipe, it's not just a case of let's
throw a big old five inch air conditioning duct
at this thing and pump it out the back of the car and put a big old
bucket-sized tailpipe on there and it's gonna look really sporty. You might a whacking great tailpipe on the end of a car, but
most likely you've got two, two and a quarter, two and
a half inch pipe running and actually along the
inside of the vehicle. And the construction, the
actual material that's used for an exhaust system,
is generally mild steel. To talk about that, let's
pop out to the junkyard, a.k.a. the front garden,
where we've got a couple of good examples. Virtually all stock exhausts
are made from mild steel. And you'll know that
exhaust systems are renowned for rust and corrosion
and you look underneath the vehicle, you see a rusty exhaust. Well why is that? It's because exhausts have
a particularly tough life. So they operate at high
temperature a lot of the time, that temperature fluctuates
as the exhaust heats up and then cools down. Plus they're filled
constantly with these noxious, nasty, corrosive, hot gasses which cause and accelerate corrosion internally. Not only is there hot gasses in there, there's also steam. So steam is a byproduct
of the combustion process and when the engine first
starts, it generates steam and that steam will
build up and pool inside the exhaust system and it
will pool particularly inside the mufflers, inside the
catalytic converters, until the exhaust gets up to temperature and then obviously that
water will then reboil and be taken out of the
tailpipe of the vehicle. But until then, it sits
inside these pipes. And if you have a vehicle
which travels lots of short journeys, and the
exhaust system never gets up to temperature, then
it will tend to corrode much more quickly because
you got this buildup of water and steam inside the exhaust system. Plus, the exhaust hangs
down underneath the vehicle, so it's in contact with
any salt on the road and just general water
and weather all the time. So exhaust systems will tend to corrode. One way around that is an
aftermarket exhaust system which is made from stainless steel. So here we have two exhaust systems, exactly the same from
this old 1987 Toyota MR2 and these are the same age. These came off vehicles the same age. This one is the stock, stainless steel, mild steel exhaust system. This one is stainless
steel and you can see the difference in wear. Even on these pipes here,
obviously they're a little gritty, but they're not heavily
corroded and pitted and rusted like this one. So stainless steel exhaust,
better, will last longer, but they're considerably more expensive You find these flexible joints on transverse mounted engines so when an exhaust fits to a transverse
mounted engine That's an engine that fits sideways it runs laterally across the vehicle instead of along the length of the vehicle like this vehicle here So what we have here is a rear-engined Rear-wheel drive vehicle With a transverse mounted engine So you can see inside, the engine runs across the vehicle. This is much more common in a front-wheel drive vehicle Or in an all wheel drive vehicle and the reason they have that flexible joint on the exhaust is that transverse mounted engines will tend to rock more because they are driving the wheels side-to-side and the actual engine in spinning side-to-side as opposed to a longitudinally mounted engine which has less of a tendency to rock And if you want to get really fancy on an aftermarket exhaust You can buy titanium... TITANIUM.. aftermarket exhausts Which not only is gonna last longer It's completely corrosion resistant It's also gonna be much lighter than a steel exhaust And it produces a completely different exhaust sound Because of the nature of the material So that is a general overview of the exhaust system. In the next series of videos we're going to look in much more detail at the headers, the manifold, the EGR system the catalyitic converter, the O2 sensors, and the silencers and mufflers. So come back in the next series of videos as we get into the details. Guys the way to learn to fix things How to repair cars and so on Is not to bounce from video to video troubleshooting each little problem as it arises. It's to get a deep level of understanding of all the systems on a car. What you need is a complete course That takes you simply from A to Z. So if you enjoy this level of detail Then get yourself over to howacarworks.com. We've got a whole series of videos: at least 20 hours Teaching you every part of modern vehicles Come and join us over there.
