Exhaust Technology (Sizing/Velocity) - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum
User Tag List

Reply
 
LinkBack Thread Tools
post #1 of 16 (permalink) Old 10-14-2005, 08:12 AM Thread Starter
Registered User
 
crossbow's Avatar
 
Join Date: May 2003
Location: USA
Posts: 11,748
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Thanks: 1
Thanked 14 Times in 9 Posts
Groans: 0
Groaned at 1 Time in 1 Post
iTrader: 0 reviews
Starting off...
http://www.rx8club.com/showthread.php?t=73332&page=1
http://www.uucmotorwerks.com/html_product/...etorquemyth.htm
http://forum.mazda6tech.com/about3061.html...ht=backpressure

Recently posted by flamearrow!

http://www.magnaflow.com/05news/magazine/05sportc.asp

http://www.isuzuperformance.com/isup...h/exhaust.html
http://www.cobbtuning.com/info/?ID=3222
http://www.isuzuperformance.com/isup...ch/intake.html

http://www.nissanperformancemag.com/june02...ofthenerds1.php
http://www.nissanperformancemag.com/july02...ofthenerds2.php
http://www.nissanperformancemag.com/...revenge_nerds/
http://www.nissanperformancemag.com/november02/nerds/
http://www.nissanperformancemag.com/december02/nerds/



Terms to google search...

Backpressure
Exhaust Sizing
helmholtz resonance
Sound Waves
Exhaust Pulse/Overlap

Quotes and posts.

Quote:
Two things. Backpressure is always bad. ALWAYS.

People always confuse having too little backpressure as being a negative..but thats not the negative. The negative is having too little exhaust velocity.

If you increase pipe diameter too much, you lose exhaust velocity, which results in less of a scavenging effect.

In a RWD vehicle, the exhaust pulses have a spot where they overlap. If you don't place a H or X junction in this area, you'll lose velocity as the pulses aren't given the ability to overlap with each other (think waves of energy). This is pretty difficult to do with a FWD vehicle, as the engine is transverse mounted, and getting equal length piping is almost impossible. Thus you usually end up with two seperate pulse junctions instead of just one.

In terms of efficency, most of the contour owners find that a single 2.5 mandrel system setup, or a dual 2.0 mandrel system (Internal Diameter), work best with the 3.0 duratec system.[/b]
Quote:
here's a simplified explanation of whats going on.

Pistons are moving up in down in a 4 stroke engine. On the exhaust stroke, the results of combustion are pushed out of the cylinder, into the cylinder head, and out the exhaust valve and exhaust port.

At this point the exhaust is incredibly hot...sometimes in excess of 1000F...its also got alot of velocity. The hot gas wants to escape, and it wants to escape NOW. The velocity of the gas is determined by the amount of force initally expelled, and the amount of volume that gas has to fill.

A small restrictive pipe would immediately fill with exhaust, and move at a considerable velocity, but excess gas would be left behind, which in the worst case scenario would actually remain in the combustion chamber and mix with the incoming fresh air, reducing power.

A large pipe would immediately absorb all the exhaust volume, but drop velocity to the extent that scavenging doesn't occur. Exhaust would still flow out, but would not be as efficent as it could be.

If the piping size is just right, the velocity is high enough so that it creates a suction effect at the cylinder head, and literarly sucks the exhaust out of the cylinder. This makes it easier for the piston to move up, and recovers a good amount of previously wasted energy.

Because there are more then one piston, you also get a pulse overlap, as each exhaust stroke adds its velocity to the previous exhaust stroke. Getting both banks to overlap can greatly increase velocity and aid in scavenging effects.

Maintaining velocity is a factor of keeping pipe length short (removing unneeded bends), keeping pipe diameter consistent (mandrel bends), and keeping the exhaust from bleeding away heat (ceramic coating).[/b]
Quote:
Sizing an exhaust is all about tuning for a specific rpm. Too large an exhaust will result in too little exhaust velocity in lower rpms, which prevents effective scavenging, and will result in a loss of low end torque. Too small an exhaust restricts the engines ability to vent exhaust gases at higher rpms, and results in a loss of power, and possible exhaust gas left in the cylinders (after the exhaust stroke ie. mixing with intake air). [/b]
Quote:
Definition of Backpressure
Restrictions in the exhaust system that slow the exit of exhaust gases from the combustion chamber.[/b]
(Edit: Updated Links: No Dead links)





To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
crossbow is offline  
The Following 2 Users Say Thank You to crossbow For This Useful Post:
Lowy (06-24-2011), SatanJoe (01-07-2014)
Sponsored Links
Advertisement
 
post #2 of 16 (permalink) Old 10-14-2005, 01:27 PM
Registered User
 
Join Date: Aug 2004
Location: Vancouver, BC
Posts: 1,284
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 0
Thanked 1 Time in 1 Post
Groans: 0
Groaned at 0 Times in 0 Posts
iTrader: 0 reviews
Send a message via MSN to OrphanBoy
I just learned a few useful things about exhausts.

Awesome finds. Kudos crossbow.
OrphanBoy is offline  
post #3 of 16 (permalink) Old 10-14-2005, 03:31 PM
Registered User
 
WickedFast's Avatar
 
Join Date: Apr 2005
Location: the future...
Posts: 165
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 0
Thanked 0 Times in 0 Posts
Groans: 0
Groaned at 0 Times in 0 Posts
iTrader: 0 reviews
Wasn't trying to "duel", Cross--I was serious. You should work for a race team or write a book.

But here's an analysis of what the Magnaflow article said:
"Low backpressure and high exhaust stream velocity can be achieved by running straight-through free-flowing mufflers and small pipe diameters [small relative to WHAT? What calculations are involved?]. The only two exceptions to this are turbocharged engines and engines optimized for large amounts of nitrous oxide. Both of these devices vastly increase the exhaust gas volume and simply need larger pipes to get rid of it all."

Sounds like all I have to do is take the TWO mufflers off my 6 and I'll have more Hp/Tq because the exhaust flow "velocity" would be faster and less restricted. Now all I have to do is to wait for someone else here to say "You idiot! You are actually LOSING hp/tq by removing those mufflers!" Talk about busting myths...

I'm just curious what kinds of sensors/tools/calculations are employed in figuring out what is the perfect pipe for a certain engine. And I wonder if some place like Magnaflow actually does those measurements and calculations, or if they just bend some bigger pipes and louder mufflers for sales and then simply claim that you get more HP/TQ. Seems the best approach is to do the math first, but in this hyped up aftermarket world you don't often see a lot of data. It seems like everyone is saying "The only way to find out is to buy it, install it, then dyno it." Doesn't give me a whole lot of confidence.
WickedFast is offline  
Sponsored Links
Advertisement
 
post #4 of 16 (permalink) Old 10-14-2005, 03:56 PM
Registered User
 
Toadster's Avatar
 
Join Date: Sep 2003
Location: Folsom, CA USA
Posts: 1,160
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 12
Thanked 2 Times in 2 Posts
Groans: 1
Groaned at 0 Times in 0 Posts
iTrader: 0 reviews
Quote:
In a RWD vehicle, the exhaust pulses have a spot where they overlap. If you don't place a H or X junction in this area, you'll lose velocity as the pulses aren't given the ability to overlap with each other (think waves of energy). This is pretty difficult to do with a FWD vehicle, as the engine is transverse mounted, and getting equal length piping is almost impossible. Thus you usually end up with two seperate pulse junctions instead of just one.
that's not entirely true!

just because a vehicle is RWD doesn't mean it has split banks and true duals to deal with

some RWD vehicles are 4-cyl, V-6 or inline-6 which have similar exhausts to our own

SOLD 2004 Performance White MAZDA6s MTX
Injen CAI | Magnaflow Catback | CP-E MAF-c | 18% Tint | Red Line MT-90

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

17x7 Kosei T1 TS Wheels & Continental ContiExtreme Contact DWS 225/45-17

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
|
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Toadster is offline  
post #5 of 16 (permalink) Old 10-14-2005, 04:15 PM
Registered User
 
Join Date: Nov 2004
Location: Flushing, NY
Posts: 676
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Thanks: 0
Thanked 5 Times in 5 Posts
Groans: 0
Groaned at 0 Times in 0 Posts
iTrader: 0 reviews
wickedfast,

Pipe sizing is not an exact science for a local tuner. Especially since cost of parts and off the shelf parts availability are limited. So basically you have to work with what you got. So your typical pipe diameters for catbacks are 2", 2 1/4", 2 1/2" etc... You can see Sport Compact Car (originator of the Build Your Own Exhaust articel) gives a rough guideline on catback sizing dependent on engine displacement.

http://www.magnaflow.com/05news/maga...sportcpg03.asp
1,500cc-2,000cc engines : 2-inch
2,100cc-2,500cc engines : 2.25-inch
2,600cc-3,000cc engines : 2.5-inch

But what is failed to be mentioned is that a lot of the exhaust velocity is lost up front in the exhaust manifolds, and catbacks complement headers output and not the other way around.

'05 6s hatch 6-speed auto: optimized AEM CAI, Racing Beat exhaust, VVME 4300k 55watt HID, Kosei K1-TS, 215-50-17 Continental DWS, Progress rear sway bar, RB front sway bar, GTSpec ladder brace, Mazdaspeed springs with 3/4" rear lift spring spacer, Bilstein HD shocks


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Have "saggy butt" syndrome? Want to even out your drop?
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
flarearrow is offline  
post #6 of 16 (permalink) Old 10-14-2005, 04:26 PM
Registered User
 
Stretch's Avatar
 
Join Date: Jun 2003
Location: Silver Spring, MD
Posts: 5,757
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 0
Thanked 6 Times in 6 Posts
Groans: 0
Groaned at 1 Time in 1 Post
iTrader: 0 reviews
Yay for more links of knowledge!

The bottom line is that equal length headers rock, and the RPM they're tuned for depend on the diameter and length. Speaker (subwoofer) modeling software works great for understanding pressure waves.

Understand suspensions? Please take the required measurements for my
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
and share them on this site.
Stretch is offline  
post #7 of 16 (permalink) Old 10-14-2005, 05:13 PM
Registered User
 
da_fatman's Avatar
 
Join Date: Sep 2005
Location: Long Island, NY
Posts: 124
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 0
Thanked 0 Times in 0 Posts
Groans: 0
Groaned at 0 Times in 0 Posts
iTrader: 0 reviews
Anybody offering the Cliff's notes? God I'm lazy.

2005 Mazda 6MT 5-Door/2006 Mazda 3MT 5-Door
da_fatman is offline  
post #8 of 16 (permalink) Old 10-14-2005, 11:15 PM Thread Starter
Registered User
 
crossbow's Avatar
 
Join Date: May 2003
Location: USA
Posts: 11,748
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Thanks: 1
Thanked 14 Times in 9 Posts
Groans: 0
Groaned at 1 Time in 1 Post
iTrader: 0 reviews
Sorry wickedfast. I blame lack of coffee! (Look at that I'm apologizing...maybe someone secretly replaced my mazda 6 with an evo IX....)

You have a 6s. Your exhaust looks like this.


A few blinks and you'll see the problem. The japanese engineers figured they'd have a good laugh at the US's expense. There are more bends and twists in the first few feet of our exhaust then turns in the nuerburgring! (Ok thats exaggerating slightly! Regardless most people get sick just looking at that).

In this type of situation, modifying the catback or mufflers will provide little or no gain, because all of the restriction is further upstream. This is verified by dyno's, as no one besides the various exhaust manufacturers have shown any gain whatsoever with any of the available catbacks on the market. (on owner dynos).

If anything, some of the catbacks are actually reducing overall power, because they're slowing down what little exhaust velocity there is, by the time it gets done going through the twists and honeycombs of doom.

Now if you were to replace the exhaust manifolds and the restrictive (and dangerous) pre-cats with the wagner or lovely CP-E manifolds, then you could start working on the exhaust velocity of the rest of the system. This is assuming that the catback is even a restriction to begin with. Its a single pipe, with two mufflers handling the exhaust streams. Not exactly restrictive. Wagner saw zero gain on the dyno on the 6i headers/ypipe and with/without the stock catback or wagner catback. I'd say if anything the catback section of the car is actually fairly well designed in terms of bends and restrictions.

Picking an exhaust size for a particular engine...tough. Two ways to do it. Wait till a bunch of other people dyno their car with tons of different exhaust sizes, write down the info, and then purchase the best setup for your application. (http://www.contour.org)

Or... Calculate the maximum volume displacement at the particular rpm you are making maximum power at. Match the exhaust size up to a similar volumetric displacement. The higher the rpm, the less velocity you'll have at lower rpms, which will result in a loss of low end power. Conversely you can setup the exhaust for max flow at your torque peak, and get a completely different effect.

Toadster, the comment on the RWD vehicles was referring to V style configurations. Aka V6, 8, 12, 24, 32, 128. Etc






To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
crossbow is offline  
post #9 of 16 (permalink) Old 10-15-2005, 11:02 AM
Registered User
 
Toadster's Avatar
 
Join Date: Sep 2003
Location: Folsom, CA USA
Posts: 1,160
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 12
Thanked 2 Times in 2 Posts
Groans: 1
Groaned at 0 Times in 0 Posts
iTrader: 0 reviews
Quote:
Originally posted by da_fatman@Oct 14 2005, 01:13 PM
Anybody offering the Cliff's notes? God I'm lazy.*
[snapback]533837[/snapback]


SOLD 2004 Performance White MAZDA6s MTX
Injen CAI | Magnaflow Catback | CP-E MAF-c | 18% Tint | Red Line MT-90

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

17x7 Kosei T1 TS Wheels & Continental ContiExtreme Contact DWS 225/45-17

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
|
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Toadster is offline  
post #10 of 16 (permalink) Old 10-15-2005, 05:56 PM
Retired Moderator
 
Jax6S's Avatar
 
Join Date: Feb 2004
Location: Jacksonville, FL
Posts: 4,053
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks: 0
Thanked 11 Times in 7 Posts
Groans: 0
Groaned at 1 Time in 1 Post
iTrader: 0 reviews
Quote:
Originally posted by crossbow@Oct 14 2005, 10:15 PM
If anything, some of the catbacks are actually reducing overall power, because they're slowing down what little exhaust velocity there is, by the time it gets done going through the twists and honeycombs of doom.
[snapback]534052[/snapback]
Oh well, a small price to pay to make the car look better.

From this:


To this:



2006 Black Mazdaspeed6
Jax6S is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome