Hiya,
On the subject of exhausts for performance, Its really not a complicated as
the posting below wants to makes it. The theories he is writing about are
sound but to be more specific
Will you keep the stock manifold ? (note - This is the most restricted part
of an LC)
If yes, then goto 2.
If no, then an expensive designed pipe work system with equal length headers
(for the pulses he was talking about) will set you back =A3800 to =A31500
depending on who makes them and what out off. Stainless steel is not always
Stainless steel if you et my drift, wall thickness, material spec, cracking
from heat expansion etc and the way the pipes are laid, gusseted etc and
the flow characteristics re all major factors in design and build cost.
And they will break especially if you combine both a turbo and a piped
manifold
So, a great solution for max power- but at a price.... so that would be a
no then !
Petrol or Diesel LC ?..........
Diesel ? - Then go with a stainless pipe from the stock scroll back (see
above, but less subject to heat cracking issues etc) from the turbo outlet
back to rear of car. Size - the same bore as the outlet scroll on the turbo,
Length.. as short as possible without melting anything, restrictions - none,
bends - none.
In fact, don=92t even bother and just leave it blowing out the scroll...lol
An you there you have it, a turbo exhaust which will give the maximum
possible power from the car.
Except, you must have bends (or melt the wing). You should have cat, you
need to keep it quiet and you need to get the heat and fumes out the back.
So a compromise is exactly that, lose the back muffler, and the middle one
smaller, less restrictive i.e less baffle plates, keep cats (IMHO), O2
sensor has to stay and the pipe bore stays at the turbo scroll size.
That=92s the compromise.
If Petrol (as in my case) - fit forced induction and do as above... lol
Truth is if its power you want a bigger turbine will always be better.
Best
Adrian
-----Original Message-----
From: "John Byrne" <[Email address removed]>
Subject: [ELCO] Emailing: Exhaust Theory.htm
Date: Wed, 1 Nov 2006 19:56:31 -0000
Reply-To: [Email address removed]
This is a multi-part message in MIME format.
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Hi Guys
I am getting to the end of my exhaust and have been thinking of the
alternatives. I read this about the bigger bore exhaust and was wondering
what people think.
cheers
john 92HDj 80 1HDT
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<H2><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Can You Tell=3D20
Me About Exhaust Systems?</FONT></H2>
<H3 align=3D3Dcenter><FONT=3D20
face=3D3D"Trebuchet MS, Arial, Helvetica">Exhaust=3D20
Theory</FONT></H3>
<H4 align=3D3Dcenter><FONT=3D20
face=3D3D"Trebuchet MS, Arial, Helvetica">From: <A=3D20
=3D
href=3D3D"http://www.overboost.com/">http://www.overboost.com/</A><!--msthe=3D
me--></FONT></H4>
We've seen too much misinformation regarding exhaust theory. =3D
What kind=3D20
of misinformation? For starters, there are a lot of people in the =3D
"Bigger=3D20
is Better" camp. We're talking about exhaust pipe diameters. Even =3D
the big=3D20
magazine editors are boldly smattering statements like, "For a =3D
turbo car,=3D20
you can't get an exhaust pipe that's too big." Also, terms like =3D
"back=3D20
pressure" and the statement, "An engine needs back pressure to run =3D
properly!" really rub us the wrong way. </P>
Let's start from the beginning. What is an exhaust system? =3D
Silly=3D20
question? Not hardly. Exhaust systems carry out several functions. =3D
Among=3D20
them are: (1) Getting hot, noxious exhaust gasses from your engine =3D
to a=3D20
place away from the engine compartment; (2) Significantly =3D
attenuating=3D20
noise output from the engine; and (3) In the case of modern cars, =3D
reduce=3D20
exhaust emissions. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Hardware </FONT></H5>
In order to give you a really good idea of what makes up an =3D
exhaust=3D20
system, let's start with what exhaust gas travels through to get =3D
out of=3D20
your car, as well as some terms and definitions: </P>
After your air/fuel mixture (or nitrous/fuel mixture) burns, =3D
you will=3D20
obviously have some leftovers consisting of a few unburned =3D
hydrocarbons=3D20
(fuel), carbon monoxide, carbon dioxide, nitrogen oxides, sulfur =3D
dioxide,=3D20
phosphorus, and the occasional molecule of a heavy metal, such as =3D
lead or=3D20
molybdenum. These are all in gaseous form, and will be under a lot =3D
of=3D20
pressure as the piston rushes them out of the cylinder and into =3D
the=3D20
exhaust manifold or header. They will also be hotter 'n Hades. =3D
(After all,=3D20
this was the explosion of an air/fuel mixture, right?) An exhaust =3D
manifold=3D20
is usually made of cast iron, and its' primary purpose is to =3D
funnel=3D20
several exhaust ports into one, so you don't need four exhaust =3D
pipes=3D20
sticking out the back of your Civic. </P>
Exhaust manifolds are usually pretty restrictive to the flow of =3D
exhaust=3D20
gas, and thus waste a lot of power because your pistons have to =3D
push on=3D20
the exhaust gasses pretty hard to get them out. So why does =3D
virtually=3D20
every new automobile sold have exhaust manifolds? Because they are =3D
cheap=3D20
to produce, and easy to install. Real cheap. Real easy. Like me. =3D
</P>
"Ok," you ask, "so now what?" Ah, good thing you asked. The =3D
performance=3D20
alternative to the exhaust manifold is a header. What's the =3D
difference?=3D20
Where a manifold usually has several holes converging into a =3D
common=3D20
chamber to route all your gasses, a header has precisely formed =3D
tubes that=3D20
curve gently to join your exhaust ports to your exhaust pipe. How =3D
does=3D20
this help? First of all, as with any fluid, exhaust gasses must be =3D
treated=3D20
gently for maximum horsepower production. You don't want to just =3D
slam-bang=3D20
exhaust gas from your engine into the exhaust system. No way, =3D
Jo-se'! Just=3D20
as the body of your '94 Eclipse is beautiful, swoopy, and =3D
aerodynamic, so=3D20
must be the inside of your exhaust system. </P>
Secondly, a header can be "tuned" to slightly alter your =3D
engines'=3D20
characteristics. We'll go in-depth into header tuning a little =3D
later. </P>
Nextly, exhaust gasses exit from your manifold or header, =3D
travel=3D20
through a bit of pipe, then end up in the catalytic converter, or =3D
"cat".=3D20
The cat's main job is to help clean up some of the harmful =3D
chemicals from=3D20
your exhaust gas so they don't end up in your lungs. In most cars, =3D
they=3D20
also do a great job of quieting things down and giving any exhaust =3D
system=3D20
a deeper, mellow tone. You'll see a lot of Self-Proclaimed Master=3D20
Technicians (SPMT's) telling people that removing a cat will get =3D
you tons=3D20
of power. There's room for debate on this, but in our experience, =3D
removing=3D20
a catalytic converter from a new car won't gain you much in the =3D
horsepower=3D20
department. It can also get you a $1500 fine if the EPA finds out! =3D
If you=3D20
drive an OBD-II equipped car, you'll also get that damn annoying =3D
CHECK=3D20
ENGINE light burnin' up your dashboard. (And for all you racers =3D
concerned=3D20
with OBD-II's fabled "limp mode", you can put your fears to rest.) =3D
</P>
From the catalytic converter, the exhaust gasses go through a =3D
bit more=3D20
pipe and then into a muffler, or system consisting of several =3D
mufflers=3D20
and/or resonators. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Are you a=3D20
muff? </FONT></H5>
Exhaust gases leave the engine under extremely high pressure. =3D
If we=3D20
allowed exhaust gasses escape to the atmosphere directly from the =3D
exhaust=3D20
port, you can well imagine how loud and cop-attracting the noise =3D
would be.=3D20
For the same reason gunshots are loud, engine exhaust is loud. =3D
Sure, it=3D20
might be cool to drive around on the street with that testosterone =3D
producing, chest-thumping, 150 decibel roar coming from your =3D
car=3D85 for=3D20
about 5.3 seconds. (Not 5.2 or 5.4 seconds=3D85 5.3.) Even the =3D
gentleman's=3D20
gentleman has gotta use a muffler, or system of mufflers, on their =3D
exhaust. </P>
Again, you may hear a few SPMT's tell you that "Borla mufflers =3D
make=3D20
horsepower!" Or "An engine needs some backpressure to run =3D
properly!"=3D20
Nonsense. A muffler can no more "make" horsepower than Wile E. =3D
Coyote can=3D20
catch roadrunners. Any technician with any dyno experience will =3D
tell you=3D20
that the best mufflers are no mufflers at all! </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Types of=3D20
Muff </FONT></H5>
Mufflers can take care of the silencing chores by three major =3D
methods:=3D20
Absorption, Restriction, and Reflection. Mufflers can use one =3D
method, or=3D20
all three, to attenuate sound that is not so pleasing to the ears =3D
of the=3D20
Highway Patrol. </P>
The absorption method is probably the least effective at =3D
quelling=3D20
engine roar, but the benefit is that "absorbers" are also best at =3D
letting=3D20
exhaust gas through. Good examples of absorbers are the mufflers =3D
found in=3D20
GReddy BL-series exhausts, DynoMax UltraFlow, and the good =3D
old-fashioned=3D20
Cherry Bomb glasspack. </P>
Absorption mufflers are also the simplest. All of the above =3D
named=3D20
mufflers utilize a simple construction consisting of a perforated =3D
tube=3D20
that goes through a can filled with a packing material, such as =3D
fiberglass=3D20
or steel wool. This is similar to simply punching holes in your =3D
exhaust=3D20
pipe, then wrapping it up with insulation. Neat, huh? </P>
Another trick absorption mufflers use to kill off noise is, =3D
well,=3D20
tricky. For example, the Hooker Aero Chamber muffler is a =3D
straight-through=3D20
design, with a catch. Instead of a simple, perforated tube, there =3D
is a=3D20
chamber inside the muffler that is much larger than the rest of =3D
the=3D20
exhaust pipe. This design abates sound more efficiently than your =3D
standard=3D20
straight-through because when the exhaust gasses enter this large =3D
chamber=3D20
they slow down dramatically. This gives them more time to dwell in =3D
the=3D20
sound insulation, and thus absorb more noise. The large chamber =3D
gently=3D20
tapers back into the smaller size of your exhaust pipe, and the =3D
exhaust=3D20
gasses are sent on their merry way to the tailpipe. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Restriction </FONT></H5>
Doesn't that word just make your skin crawl? It's right up =3D
there in the=3D20
same league with words like "maim" and "rape". </P>
Obviously, a restrictive muffler doesn't require much =3D
engineering=3D20
expertise, and is almost always the least expensive to =3D
manufacture. Thus,=3D20
we find restrictive mufflers on almost all OEM exhaust systems. We =3D
won't=3D20
waste much time on the restrictive muffler except to say that if =3D
you got=3D20
'em, you might not want to flaunt 'em. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Reflection</FONT></H5>
Probably the most sophisticated type of muffler is the =3D
reflector. They=3D20
often utilize absorption principles in conjunction with reflection =3D
to make=3D20
the ultimate high-performance silencer. Remember any of your =3D
junior high=3D20
school math? Specifically, that like numbers cancel each other =3D
when on a=3D20
criss-cross? That's the same principal used by the reflective =3D
muffler.=3D20
Sound is a wave. And when two like waves collide, they will =3D
"cancel" each=3D20
other and leave nothing to call a corpse but a spot of low-grade =3D
heat.=3D20
</P>
There are numerous engineering tricks used in the reflective =3D
muffler.=3D20
Hedman Hedders makes a muffler that looks a lot like a glasspack. =3D
In fact,=3D20
it is a glasspack with a catch. The outer casing is sized just-so, =3D
so that=3D20
high-pitched engine sound (what we deem "noise") is reflected back =3D
into=3D20
the core of the muffler=3D85 where those sound waves meet their =3D
maker as they=3D20
slam right into a torrent of more sound waves of like wavelength =3D
coming=3D20
straight from the engine. And, this muffler is packed with a lot =3D
of=3D20
fiberglass to help absorb any straggling noise that might be =3D
lagging=3D20
behind. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">The Exhaust=3D20
Pulse</FONT></H5>
To gain a more complete understanding of how mufflers and =3D
headers do=3D20
their job, we must be familiar with the dynamics of the exhaust =3D
pulse=3D20
itself. Exhaust gas does not come out of the engine in one =3D
continuous=3D20
stream. Since exhaust valves open and close, exhaust gas will =3D
flow, then=3D20
stop, and then flow again as the exhaust valve opens. The more =3D
cylinders=3D20
you have, the closer together these pulses run. </P>
Keep in mind that for a "pulse" to move, the leading edge must =3D
be of a=3D20
higher pressure than the surrounding atmosphere. The "body" of a =3D
pulse is=3D20
very close to ambient pressure, and the tail end of the pulse is =3D
lower=3D20
than ambient. It is so low, in fact, that it is almost a complete =3D
vacuum!=3D20
The pressure differential is what keeps a pulse moving. A good Mr. =3D
Wizard=3D20
experiment to illustrate this is a coffee can with the metal ends =3D
cut out=3D20
and replaced with the plastic lids. Cut a hole in one of the lids, =3D
point=3D20
it toward a lit candle and thump on the other plastic lid. What =3D
happens?=3D20
The candle flame jumps, then blows out! The "jump" is caused by =3D
the=3D20
high-pressure bow of the pulse we just created, and the candle =3D
goes out=3D20
because the trailing portion of the pulse doesn't have enough=3D20
oxygen-containing air to support combustion. Neat, huh? </P>
Ok, now that we know that exhaust gas is actually a series of =3D
pulses,=3D20
we can use this knowledge to propagate the forward-motion to the =3D
tailpipe.=3D20
How? Ah, more of the engineering tricks we are so fond of come in =3D
to play=3D20
here. </P>
Just as Paula Abdul will tell you that opposites attract, the =3D
low=3D20
pressure tail end of an exhaust pulse will most definitely attract =3D
the=3D20
high-pressure bow of the following pulse, effectively "sucking" it =3D
along.=3D20
This is what's so cool about a header. The runners on a header are =3D
specifically tuned to allow our exhaust pulses to "line up" and =3D
"suck"=3D20
each other along! Whoa, bet you didn't know that! This brings up a =3D
few=3D20
more issues, since engines rev at various speeds, the exhaust =3D
pulses don't=3D20
always exactly line up. Thus, the reason for the Try-Y header, a =3D
4-into-1=3D20
header, etc. Most Honda headers are tuned to make the most =3D
horsepower in=3D20
high RPM ranges; usually 4,500 to 6,500 RPM. A good 4-into-1 =3D
header, such=3D20
as the ones sold by Gude, are optimal for that high winding =3D
horsepower=3D20
you've always dreamed of. What are exhaust manifolds and stock =3D
exhaust=3D20
systems good for? Besides a really cheap boat anchor? If you think =3D
about=3D20
it, you'll realize that since stock exhausts are so good at =3D
restricting=3D20
that they'll actually ram the exhaust pulses together and actually =3D
make=3D20
pretty darn good low-end torque! Something to keep in mind, =3D
though, is=3D20
that even though an OEM exhaust may make gobs of low-end torque, =3D
they are=3D20
not the most efficient setup overall, since your engine has to =3D
work so=3D20
hard to expel those exhaust gasses. Also, a header does a pretty =3D
good job=3D20
of additionally "sucking" more exhaust from your combustion =3D
chamber, so on=3D20
the next intake stroke there's lots more fresh air to burn. Think =3D
of it=3D20
this way: At 8,000 RPM, your Integra GS-R is making 280 pulses per =3D
second.=3D20
There's a lot more to be gained by minimizing pumping losses as =3D
this busy=3D20
time than optimizing torque production during the slow season. =3D
</P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">General=3D20
Rules of Thumb with Headers </FONT></H5>
You will undoubtedly see a variety of headers at your local =3D
speed shop.=3D20
While you won't be able to determine the optimal power range of =3D
the=3D20
headers by eyeballing them, you'll find that in general, the best=3D20
high-revving horsepower can be had with headers utilizing larger =3D
diameter,=3D20
shorter primary tubes. Headers with smaller, longer primaries will =3D
get=3D20
you
slightly better fuel economy and better street =3D
driveability. With=3D20
four cylinder engines, these are also usually of the Tri-Y design, =3D
such as=3D20
the DC Sports and Lightspeed headers. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, Helvetica">Do =3D
Mufflers=3D20
"Make" Horsepower? </FONT></H5>
The answer, simply, is no. The most efficient mufflers can only =3D
employ=3D20
the same scavenging effect as a header, to help slightly overcome =3D
the loss=3D20
of efficiency introduced into the system as back pressure. But I =3D
have yet=3D20
to see an engine that made more power with a muffler than an open =3D
header=3D20
exhaust. "So," you ask, "what the hell is the best flowing muffler =3D
I can=3D20
buy?" </P>
According to the flowbench, two of the best flowing units you =3D
can buy=3D20
are the Walker Dyno Max and the Cyclone Sonic. They even slightly =3D
out flow=3D20
the straight through designs from HKS and GReddy BL series. =3D
Amongst the=3D20
worst, are the Thrush Turbo and Flow Master mufflers. We'll flow =3D
some of=3D20
the newer mufflers as they become available at our local Chief =3D
auto. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Resonators </FONT></H5>
On your typical cat-back exhaust system, you'll see a couple of =3D
bulges=3D20
in the piping that are apparently mini-mufflers out to help the =3D
big=3D20
muffler that hangs out back. These are called Helmholtz Resonators =3D
and are=3D20
very similar to glasspacks. The main difference is that firstly, =3D
there is=3D20
no sound-absorbing fiberglass or steel wool in a Resonator. And =3D
secondly,=3D20
their main method of silencing is the reflective principle, not=3D20
absorption. An easy way to tell the difference between a glasspack =3D
and a=3D20
true Helmholtz Resonator is to "ping" one with your finger. A =3D
glasspack=3D20
will make a dull thud, and a true Resonator will make a clear =3D
"ping!"=3D20
sound. </P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Turbos </FONT></H5>
Another object that might be sitting in your exhaust flow is a =3D
turbine=3D20
from a turbocharger. If that is the case, we envy you. </P>
Not only that, but turbos introduce a bit of backpressure to =3D
your=3D20
exhaust system, thus making it a bit quieter. All of the typical=3D20
scavenging rules still apply, but with a twist. Mufflers work =3D
really well=3D20
now! Remember, one of the silencing methods is restriction, and a =3D
turbine=3D20
is just that, a restriction. </P>
This is actually where the term "turbo muffler" is coined. =3D
Since a=3D20
turbine does a pretty good job of silencing, OEM turbo mufflers =3D
can do a=3D20
lot less restricting to quiet things down. Of course, aftermarket=3D20
manufacturers took advantage of this performance image and branded =3D
a lot=3D20
of their products with the "turbo" name in order to drum up more =3D
business=3D20
from the high performance crowd. We're sad to say that the term =3D
"turbo"=3D20
has been bastardized in this respect, and would like that to serve =3D
as a=3D20
warning. A "turbo" muffler is not necessarily a high-performance =3D
muffler.=3D20
</P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Pipe Sizing </FONT></H5>
We've seen quiet a few "experienced" racers tell people that a =3D
bigger=3D20
exhaust is a better exhaust. Hahaha=3D85 NOT. </P>
As discussed earlier, exhaust gas is hot. And we'd like to keep =3D
it hot=3D20
throughout the exhaust system. Why? The answer is simple. Cold air =3D
is=3D20
dense air, and dense air is heavy air. We don't want our engine to =3D
be=3D20
pushing a heavy mass of exhaust gas out of the tailpipe. An =3D
extremely=3D20
large exhaust pipe will cause a slow exhaust flow, which will in =3D
turn give=3D20
the gas plenty of time to cool off en route. Overlarge piping will =3D
also=3D20
allow our exhaust pulses to achieve a higher level of entropy, =3D
which will=3D20
take all of our header tuning and throw it out the window, as =3D
pulses will=3D20
not have the same tendency to line up as they would in a smaller =3D
pipe.=3D20
Coating the entire exhaust system with an insulative material, =3D
such as=3D20
header wrap or a ceramic thermal barrier coating reduces this =3D
effect=3D20
somewhat, but unless you have lots of cash burning a hole in your =3D
pocket,=3D20
is probably not worth the expense on a street driven car. </P>
Unfortunately, we know of no accurate way to calculate optimal =3D
exhaust=3D20
pipe diameter. This is mainly due to the random nature of an =3D
exhaust=3D20
system -- things like bends or kinks in the piping, temperature=3D20
fluctuations, differences in muffler design, and the lot, make =3D
selecting a=3D20
pipe diameter little more than a guessing game. For engines making =3D
250 to=3D20
350 horsepower, the generally accepted pipe diameter is 3 to 3 =3DBD =3D
inches.=3D20
Over that amount, you'd be best off going to 4 inches. If you have =3D
an=3D20
engine making over 400 to 500 horsepower, you'd better be happy =3D
capping=3D20
off the fun with a 4 inch exhaust. Ah, the drawbacks of =3D
horsepower. The=3D20
best alternative here would probably be to just run =3D
open
exhaust! =3D20
</P>
<H5><FONT face=3D3D"Trebuchet MS, Arial, =3D
Helvetica">Other Rules </FONT></H5>
A lot of the time, you'll hear someone talking about how much =3D
hotter=3D20
the exhaust system on a turbo car gets than a naturally aspirated =3D
car.=3D20
Well, if you are catching my drift so far, you'll know that this =3D
is a=3D20
bunch of BS. The temperature of exhaust gas is controlled by =3D
air/fuel=3D20
mixture, spark, and cam timing. Not the turbo hanging off the =3D
exhaust=3D20
manifold. </P>
When designing an exhaust system, turbocharged engines follow =3D
the same=3D20
rules as naturally aspirated engines. About the only difference is =3D
that=3D20
the turbo engine will require quite a bit less silencing. </P>
Another thing to keep in mind is that, even though it would be =3D
really=3D20
super cool to get a 4 inch, mandrel bent exhaust system installed =3D
under=3D20
your car, keep in mind that all of that beautiful art work won't =3D
do you a=3D20
bit of good if the piping is so big that it gets punctured as you =3D
drag it=3D20
over a speed bump! A good example of this is the 3 inch, cat back =3D
system=3D20
sold by Thermal Research and Development for the =3D
Talon/Laser/Eclipse cars.=3D20
The piping is too big to follow the stock routing exactly, and =3D
instead of=3D20
going up over the rear suspension control arms, it hangs down =3D
below the=3D20
mechanicals, right there in reach of large rocks! So when =3D
designing your=3D20
Ultimate Exhaust System, do be careful! =3D
</P> </FONT></TD></TR><!--msnavigat=3D
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