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Home > Performance Mods > Exhaust > What you need to know about exhaust (in general)

What you need to know about exhaust (in general)

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Web


Reg'd: Apr 17, 2006

THE SHADOW

Parts of an exhaust are a good place to start right? Might as well know what it is you're looking at rather than just talking about it.

Header(s)...exhaust manifold:
This is a COMMONLY misused phrase by many tuners. Most people believe that their 4 cylinder or inline 6 has "headers." Well, that is incorrect. In special cases (Flat 4 and some inline 6 engines), the exhaust manifold may be split into multiple sections but...our tC has a single exhaust header. The main purpose of a header(s) is to increase the exhaust velocity coming out of the block by scavenging (pulling combusted A/F mixtures from each cylinder) it more efficiently.

An exhaust manifold can either be cast or individual runners. A "cast" manifold is one that is basically pulled out of a mold and the individual runners are molded into one scavenging section of the exhaust. The image below is a CAST manifold:

Note: Although there are 2 main runners (tubes going to the exhaust collector), each exhaust port does NOT have it's own runner.

Below is a header (with individual runners):
Note: Each exhaust port has it's OWN runner (tube).

Down pipe\Spipe:
This is the exhaust pipe that the header connects to on one end and then connects to the midpipe on the other. For our tC, this is called the Spipe due to its design that looks like an "S". Upgrading this pipe helps the exhaust flow from the header much more fluidly and at an increased pace. This is an example of ours:


Catalytic convertor:
This is an emission regulated piece of your exhaust pipe that helps filter out some of the more harmful gases produced by the combustion process. Mainly, NO2 (not N20 or Nitrous), CO and CO2 are the gasses that elevate the greenhouse gas epidemic. The convertor also acts as a restriction on the exhaust flow/velocity and helps keep backpressure (pressure that is held within the exhaust pipe to keep the scavenging process of the header(s) efficienty and not "over-kill") so that the exhaust does not decrease the output performance of the engine.


Mid-pipe:
Some vehicles have what is called an X-pipe, Y-pipe or H-pipe as well. Mainly, those are V8 engines that actually have 2 headers and for performance reasons (along with some emission reasons) require specially designed exhaust midpipes. The midpipe is what connects the Spipe to the rear section of our exhaust. Within this pipe, the catalytic convertor is welded along with another "buldge" called a resonator. The midpipe helps the exhaust flow continue to the exiting muffler at the rear of the car.
Below is a generic example (white is the Catalytic Convertor and the box is the resonator:
[img]http://www.eng.hawaii.edu/~panos/midpipe.jpg[/img]

Resonator:
A resonator is somewhat of another muffler (silencer) that is placed in the exhaust pipe to further slow the exhaust velocity and cancel "noise." By "noise" I mean the rasp and rattling sound you hear a lot of tuner cars have when they put a header on their car with a large exhaust pipe. Resonators can work in a few ways: Bouncing exhaust sound waves against baffles (metal plates in way of the exhaust), absorbing those sound waves into a fiberglass packing withint their shell, creating waves/ribs in the metal of the resonator to cause the exhaust to become turbulant and bounce against itself or a perforated tube and chamber style.

Fiberglass packed resonators:
These resonators work "OK" but still allow a lot of "noise" to pass through. They do not impead the exhaust flow nearly as much as a baffled resonator, but they don't cancel the noise out nearly as well either. Below is an example and note the holes in it:

Note: The holes in the tube allow exhaust to flow out into the larger chamber where there is a fiberglass material packed to absorb the noise.

Baffled resonators:
These type utilize the noise cancellation technique of bouncing sound waves against one another thus, deadening their noise. This way creates a little more back pressure due to it impeading the exhaust flow a bit, but works the best for sound supression from what I have done on my tC. Below is an example of a baffled resonator:

Note: This one uses a spiral baffle technique to funnel the exhaust into a tightly spiral reducing the amount of noise waves bouncing around in an open chamber. It also allows a straight through pass to reduce backpressure (I have this one and love it).

Ribbed resonators: (for his and her pleasure....jp)
This style uses a ribbed pattern to create turbulance in the exhaust and help it bounce off itself. The exhaust sound waves will hit the ridges and ricochet in another direction colliding with other waves and deadening the noise. This frees up a lot of backpressure so it may hurt performance if you don't have ample HP pushing through the engine:


Perforated Tubes:
This is the same style as the fiberglass packed type but minus the packing. This is simply a tube with a lot of holes inside another chamber. The sound waves pass through the holes and into the chamber, which creates multiple collision areas and deadens the noise:

Note:This is the same image as the fiberglass packed tube b/c the only difference in this and the other is that the other has fiberglass between the perforated tube and outshell and this one does not.


Axle back/Muffler:
This is the final resonance of the exhaust system and the portion that can change the exiting noise of the exhaust the most. There are MANY types of exhaust just like resonators but, all are meant to perform the same function. Create a final reduction in exhaust emissions and deaden exhaust output noise. I won't list the styles b/c you should already be able to understand how each would work. It's the same sequence as the resonators.


Now........................

Backpressure:
This is the pressure that is built up in the exhaust flow that allows the scavenging process of the Header(s) to perform at their desired levels. The less backpressure, the more scavenging that is done and faster. The downside: Backpressure is crutial for small engines and torque build up. Stock backpressure helps give the tC ~160 lb/ft of torque but as you begin to release that pressure, the torque begins to move further up the rpm band. By this I mean that after releasing this pressure, you won't have the same amount of torque at 2000 rpms as you did with a stock exhaust system. This is due to the fact that the engine has to work harder to produce the same amount of HP/TQ, but it will come into play a few seconds (relative time) later in the power band.



4 cylinder engines are usually very "high strung" engines and usually react NEGATIVELY to big exhaust pipe swaps. For our tC (and please don't think I'm just talking out of my butt b/c I've gone through 4 different exhaust setups and now have a completely custom one that works great), the maximum INNER diameter I would go on an exhaust is 2.25". A lot of people/vendors sell 2.5" exhausts but when you really measure the inside diameter, it's about 2.25 to 2.35". 2.5"+ would be best for Turbo engines b/c they require faster exhaust scavenging to spool the turbo and create boost.


Turbo exhausts:
Turbos require faster scavenging, as mentioned, so that the exhaust veloctiy can spool the turbo. The exhaust passes by the exhaust fins of the turbo and spins them causing more air to be drawn in on the intake side of the turbo. This increased induction will cause increased exhaust and so forth. More induction + More exhaust = MORE BOOST. This is only for turboed cars though.

Supercharged exhausts:
S/C are belt driven and require engine power to create power. The important thing to note with this engine setup is that it is pretty similar to a N/A (naturally aspirated) setup. Both require engine power to create more power but the S/C adds the boost factor into play. As the engine creates the power, it compresses it in the intake manifold creating a denser A/F mixture. This denser mixture is harder to combust (pressure wise) but when it does, it's more explosive than stock and can create more pressure forced upon the pistons. This amount of pressure increases the horsepower in the engine thus, increasing the exhaust velocity. BUT, if you increase the exhaust pipe to a 3" pipe, it's still going to take a bit longer to actually create enough pressure in that pipe to bring that extra power into the low end of the rpm band.


This is just the basics of exhausts so hopefully this helps some of you.


I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. A.E.
[#] Aug 08, 2007 02:29pm
RouletteTc


Reg'd: Jul 06, 2007

Scion Guru

That pretty much clear up a lot of "gray" areas for me. Thanks bud.


-Thanks for the sig Aciidsneaker
[#] Aug 08, 2007 02:33pm
Web


Reg'd: Apr 17, 2006

THE SHADOW

Glad to help.


I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. A.E.
[#] Aug 08, 2007 02:35pm
SqMK


Reg'd: Dec 31, 1969

Ultimate Window Washer

Very nice write up, Jeff!

[#] Aug 08, 2007 02:40pm
Web


Reg'd: Apr 17, 2006

THE SHADOW

SqMK wrote:
Very nice write up, Jeff!


Thanks, I hope it helps people getting to know their car.


I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. A.E.
[#] Aug 08, 2007 02:41pm
FloridaGirl


Reg'd: Nov 12, 2006



Wow thats a great explanation Webster!!!! Thanx I needed that!


[#] Aug 08, 2007 02:51pm
soCAL-tc


Reg'd: Oct 24, 2006

Scion Guru

^you're a madman yoda, great write up..!

[#] Aug 08, 2007 02:53pm
swiftprov

Reg'd: Jun 14, 2007

Scion Guru

very nice Web
lots of info and not hard to understand at all!!

[#] Aug 08, 2007 03:01pm
Orin


Reg'd: Dec 08, 2005


excellent! This should help clear up a lot of things. Nicely done

[#] Aug 08, 2007 03:10pm
SuperBat_Mobile


Reg'd: Jun 12, 2007

Detailer

That was a great write-up. Very informative!


[img]http://i186.photobucket.c...8/slickshottc/yyddffg.jpg[/img]
[#] Aug 08, 2007 03:10pm
grlswannadance


Reg'd: Apr 08, 2007

Godlike Advisor

jeeez thats alotta info
thanx!

a car is a girls toy too ;]

-- www.myspace.com/pinksquadowner
--www.itsmyscion.com/caligirltiffy
[#] Aug 08, 2007 03:14pm
curtislo9


Reg'd: Jun 20, 2007

Master Mechanic

you are the man.

[#] Aug 08, 2007 04:38pm
Mayo


Reg'd: Feb 14, 2007

The Guru

I love this thread.

Great job Web, you've done it again!


"I have an idea! An idea so smart, my head would explode if I even began to know what I was talking about." - Peter Griffin
-- Want to post a "For Sale" thread? Check out the rules first.
[#] Aug 08, 2007 05:20pm
rlinbatonrouge


Reg'd: Jul 31, 2007

Tech Advisor

This is a good thread. I wish some of my guys would read what you have posted about s/c's and exhaust. Some just won't listen and would put 5" pipes if they could fit them....

[#] Aug 09, 2007 09:28am
Web


Reg'd: Apr 17, 2006

THE SHADOW

So many people don't understand that some backpressure is a GOOD thing b/c it helps the engine work efficiently to produce power. If the pipes are too big (except for turbos), the engine is working harder at each rpm to produce the power it could have produced, at the same rpm, with a smaller pipe.

A lot of it is common sense and I always use the straw vs. pipe breath test. Tell your guys to try this:

Get a coffee straw and a cup of water. Now blow through the straw into the water and see the turbulance you produce (this will be a stock setting for vehicles). Now, get a slightly larger straw (restaurant sized) and do the same thing. Note that blowing through the straw using the same force as you did in the coffee straw will create less turbulance in the water as compared to the same force going through the smaller straw. Finally, get something like a toilet paper roll and blow with the same amount of force through it. Note, there is very little turbulance but you get winded faster.

If you increase the force of air your are blowing out, then yes...you will out do the turbulance from the coffee straw but...you will have used MORE force to produce the same amount of turbulance. The resistance you feel in each straw while blowing is the equivalent to backpressure in an exhaust.


Hope that helps and maybe it'll help explain it to them guys. That's how I explained it to my buddy with his S/C Cobalt and he got it pretty quick.


I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. A.E.
[#] Aug 09, 2007 09:41am

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