Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Go Back   Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum > General > Tech Talk > S Chassis

S Chassis Technical discussion related to the S Chassis such as the S12, S13, S14, and S15.


Closed Thread
 
Thread Tools Display Modes
Old 08-06-2008, 12:33 PM   #61
eek
Zilvia FREAK!
 
Join Date: Feb 2004
Location: California
Age: 40
Posts: 1,025
Trader Rating: (29)
eek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud ofeek has much to be proud of
Feedback Score: 29 reviews
If back pressure is such a good thing for NA cars, why do alot of the NA hondas run short pipes right off the header or run a e-cut out off the header? Not just hondas in general, but I've seen many cars on the dyno both na and boosted run e-cut outs right after the header or downpipe and get gains.
eek is offline  
Sponsored Links
Old 08-06-2008, 02:41 PM   #62
waltnuts42
 
Join Date: Aug 2008
Location: Chicago
Age: 32
Posts: 10
Trader Rating: (0)
waltnuts42 is on a distinguished road
Feedback Score: 0 reviews
Those people who are saying we want back pressure are just very confused. It is not that people argue for the smaller exhaust because it creates more back pressure, it is because of the velocities, timing, and strength of the low pressure pulses, which is the technical part of scavenging.

But first an explanation of the exhaust basics so everybody has an idea what we are talking about because a lot of confusion is people having no idea what they are reading and then pass on their god awful interpretation of what they just read.

There are mainly two ways overall, through the theories and purposes of the exhaust, in which incomplete removal of exhaust gases reduce performance.

One is a little thing called volumetric efficiency. This little wonder decreases when residual gases take up space in the cylinder. The other is the higher cylinder pressures from incomplete exhaust blowdown will force burnt gasses into the intake port when it opens.

Blowdown occurs during the period between the exhaust valve opening and bottom dead center. This is where the exhaust gases are expelled from the cylinder, from higher cylinder pressure than the pressure in the exhaust, before the actual exhaust stroke begins (piston starts moving up). The left over gases not discharged during blowdown must be physically "pumped" out of the cylinder during the exhaust stroke, which lowers power due to pumping work.

The pressure wave of the exhaust leaving the cylinder is known as a compression wave. When this wave reaches the end of the header primary tube (the collector) it then expands, creating a suction wave (low pressure). This wave travels back up the primary tube and if tuned right it should just reach the exhaust valve just as the overlap is finished. What this does with the low pressure is evacuates all the spent gases and in turn will also create an effect known as inertia supercharging where it increases the velocity of the intake charge and actually creates higher intake charge pressure in the cylinder than it would be normally be and allows the ability to reach VE over 100% if done right. That, my friends, is scavenging.

Now all this explains how the exhaust system works. If you understand what you just read you should realize why we go after velocity (NOT DIRECTLY VOLUME). Just bigger pipes (more volume) reduces the velocity and velocity values below whatever the particular motor needs will not have strong enough suction wave to completely scavenge the cylinder which hinders the blowdown process and decreases volumetric efficiency.

Now finding the right header length and diameter is how you "tune" your headers. Having the right length times the suction pulse (at its optimum velocity) to reach the exhaust valve at its closing and the diameter which determines velocity and must be correctly sized to utilize all the strength of the suction pulse.

With all of this i mentioned NOTHING about obtaining back pressure and which few before have correctly stated WE DO NOT WANT.
This idea also goes along with the ports which is why if you want a truly good job on your ports you should leave it to the pros. NO exhaust can correct a poor port job.

I tend to explain things in which i understand but i think i did a decent job on this so hopefully this will clear some things up. Any further questions or if you do not understand part of this ask and i will try to explain it in another way or hopefully someone can.
waltnuts42 is offline  
Old 08-06-2008, 02:44 PM   #63
waltnuts42
 
Join Date: Aug 2008
Location: Chicago
Age: 32
Posts: 10
Trader Rating: (0)
waltnuts42 is on a distinguished road
Feedback Score: 0 reviews
Now i know alot of people are ignorant and lazy and will not read what i wrote because of its length so i am writing a short post for those people to read and go back and read the long post.
waltnuts42 is offline  
Old 08-07-2008, 09:37 PM   #64
mystery_elmo
 
mystery_elmo's Avatar
 
Join Date: Aug 2008
Location: San Leandro
Age: 35
Posts: 32
Trader Rating: (0)
mystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond reputemystery_elmo has a reputation beyond repute
Feedback Score: 0 reviews
Send a message via AIM to mystery_elmo
Quote:
Originally Posted by BigVinnie View Post
Fuck you Tyler keep this up and I will fire you from work.... You even have a snap shot of one of your gay ass video games as your avatar!!!
I am going to kill your MX6 at the track today.

tsk tsk tsk....
hey that game is not gay!! ur gay! u will not fire me from work cuz im god aka now ur boss.... and no u will not kill my mx-6 cuz its alive and kicking!! unlike ur 240! hahahaha so yea whos ur daddy?!
and ur avatar is gayer then mine!! u actually have a gay person in it!! hahahahahahahaha
mystery_elmo is offline  
Old 03-18-2009, 07:35 PM   #65
s14drifter69
Leaky Injector
 
s14drifter69's Avatar
 
Join Date: Nov 2008
Location: Miami, Fl
Age: 33
Posts: 141
Trader Rating: (1)
s14drifter69 is an unknown quantity at this point
Feedback Score: 1 reviews
make the piping 2-2.5". i have it like that but im going turbo
__________________
s14drifter69 is offline  
Old 03-18-2009, 08:22 PM   #66
The Chad
Zilvia Addict
 
The Chad's Avatar
 
Join Date: Feb 2007
Location: Richmond, VA
Age: 40
Posts: 943
Trader Rating: (0)
The Chad is just really niceThe Chad is just really niceThe Chad is just really niceThe Chad is just really niceThe Chad is just really niceThe Chad is just really niceThe Chad is just really niceThe Chad is just really niceThe Chad is just really nice
Feedback Score: 0 reviews
What inclines people to revive dead threads from the grave? This thread was a fail back in 2008...it is no better now, please close this or at least stop contributing. Thank you.
The Chad is offline  
Old 03-18-2009, 08:46 PM   #67
S14DB
AFC #1
 
S14DB's Avatar
 
Join Date: Oct 2003
Location: 昨晩あなたのお母さんの家
Posts: 20,181
Trader Rating: (3)
S14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfectionS14DB is close to perfection
Feedback Score: 3 reviews
Quote:
Originally Posted by The Chad View Post
What inclines people to revive dead threads from the grave? This thread was a fail back in 2008...it is no better now, please close this or at least stop contributing. Thank you.
To post shit that has been proven untrue years beforehand...
__________________
Comments should be taken as Opinions not as Statements of Fact
S14DB is offline  
Closed Thread

Bookmarks


Thread Tools
Display Modes

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

Forum Jump


All times are GMT -6. The time now is 09:17 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
vB.Sponsors
Copyright © 1998 - 2019, Zilvia.net™