<font face="Verdana, Arial" size="2">Originally posted by Jza:
You could always get that fuel additive that makes your exhaust smell like strawberries..

LOL</font>

<font face="Verdana, Arial" size="2">Originally posted by SSC:
Far be it from me to claim superior knowledge but catalytic converters change carbon monoxide to carbon dioxide. Carbon dioxide is supposed to be less hazardous to the ozone. Carbon monoxide is what plants soak up to produce oxygen. In a city where there is a lot of plants/trees the monoxide would be soaked up before it even had a chance to reach the ozone layer. It not like it shoots straight up in the air when expelled it disperses and plants soak it up. There is a 30 year study in the Brazilian rain forest to test the results of this theroy and on year 22 now the results are looking very good, "No dead trees". Where as LA where smog is considered the NO.1 enemy and catalytic converters have been mandatory since 73 the level of pollution has worsened. There is no one in their right mind who can claim that automobiles are killing the environment, its heavy industry who we would be pointing the finger at! An example would be pre motorized New York. In the 1880-1900 New York was the industrial capitol of the united sates manufacturing all sorts of material from textiles to processing Oil for use in lamps as well as keeping the machinery at the factories spinning. One can take from this that actually producing oil causes more ill effects than running it through the combustion process, I believe that pollution level was considered to be 40 parts per million which is highly lethal. Again I site California and they're many oil processing plants along the coast. So far we can only see the effects of modern oil processing for a reduced amount of pollutants in the air as well as the reduce amount of coal being used for heating as back in 1890. Since 1973 to present there is very little change in the smog situation in California and any dramatic change can be contributed to the closure of industrial facilities not cleaner running automobiles. Back to subject in my twisted way of course, removal of the converter seems to improve fuel economy, every little bit helps.
IMO I would rather have a car that's better on gas and produces plant food "also improves HP power mind you" than one that's supposedly safer for the ozone layer yet produces more waste. BTW that Hole up there in the ozone is still getting bigger even though we banned aerosol hair spray. Subject, Yes the removal of the cat will give you more power!
If were killing the earth we might as well pave it! J/K I love the earth and would rather nuke it and let nature start over than live in a desolate planet.
Dont let Al Gore read this, He might kill himself!
SSC

[This message has been edited by SSC (edited July 17, 2001).]</font>

Originally posted by joshwilson3
I believe that you are wrong, SSC. Plants use carbon dioxide to make oxygen, not carbon monoxide. Humans use this oxygen in the air and make carbon dioxide. So when you exhale, you are breathing out carbon dioxide. If plants used carbon monoxide to produce oxygen, then we humans would all be dead, because carbon monoxide is poisonous to us. That is why they make carbon monoxide detectors for homes. Carbon monoxide is odorless and tasteless.


"I'm dancing on the fuking graves!"

:lala:

Originally posted by 25THRSS
Whats this crap about losing torque? That is absolute bs! Any time you reduce a load on the engine it will produce more hp and torque! Please people, don't spout out bs about how you need backpressure. Backpressure is bad, no if's and's or but's about it.

Originally posted by MrDude_1
a specific amount is good and helps the low end.

however, most 3rdgens already have enough because of the y pipe... so its a moot point.........


if you want more info, do a goo search here: www.google.com you'll find alot more info on the subject then on just this site.

Originally posted by 25THRSS
NOOOOOOOOOOOOOO, any amount of backpressure is bad! Any, and all backpressure is bad, very bad. You want 0, absolutely no backpressure at all. That is what will produce the most power AND torque. Say it with me now people; Backpressure is bad, velocity is good. Please don't start this backpressure bull**** again.

Originally posted by MrDude_1
btw, do you also believe the larger the primary tube on the header, the better it is for the engine??

Originally posted by 25THRSS
If you had actually read what I posted then you wouldnt even ask a dumb question like that. I said backpressure is bad and velocity is good. When choosing the right headers and exhaust system you have to take into account how much horsepower you will be making, aka how much gases you will be pushing out to achieve the maximum amount of velocity without creating backpressure. You can actually go too big which would slow the escaping gasses down and in effect create backpressure, so see I am not the "ill informed" one. It seems that you are. I will say again, BACKPRESSURE IS BAD!

Originally posted by MrDude_1
heh, cool. atleast you know somthing.

now on to your generic "the engine is a pump" outlook.

first of all. i agree accessive backpressure is bad. also, i agree that 99% of all thirdgens already have more then enough back pressure.


lets step away from 3rdgens and talk engines for a min.

now obviously, the more radical the engine, the more noticable the diff...


imagine a engine with a cam that has alot of overlap and a backpressure free exhaust system.

at lower RPM, as the air/fuel charge pours in, rather then going to the bottom of the cyl, it wants to flow out the exhaust port. you lose a little power that way..... that would be a way over simplified example... but think about it a bit...


in anycase, i still suggest you do a search. im leaving for work so i cant search for you.

just noticing that around here there is so much false information going around about backpressure and how it is needed.
so I am going to try my best to address how backpressure is NOT needed as well as a few other ideas


first thing I want to talk about it how people say backpressure is needed because it keeps velocity up and helps scavenging.
I see to major problems with that. first backpressure is in itself a resistance to flow correct? what happens when you put resistance to flow? it slows down correct? so if there is resistance in the system slowing the exhuast gas down how is it supposed to keep velocity up? it can't. second thing I is with how since backpressure keeps velocity up it makes it to where the first exhuast pulse helps create a vacuume to help suck the next exhuast pulse out. here lies the problem with that the words vacuume and sucking mean low pressure or no pressure. the word backpressure makes it sound as though there is pressure in the system. so which is it? you can't have a both pressure no vacuume at the same time in the same spot now can you?

also just want to take care of a few example of how backpressure works and how they are not able to be used and why.
backpressure is good it speeds the exhuast gasses up. example put your finger over a garden hose and see how the water comes out of there a lot faster.

yes the water does come out of there a lot faster but there is a difference with this when trying to talk about an exhuast system. first on the water hose it is a static system. no pulses or anything of the sort. an exhuast system has pulses in it so generally there isn't a constant pushing force. instead once the pulse is pushed out it more or less is left on it's own. if it finds resistance since there is still no static pressure behind it that pulse slows way down. second the actuall flow through the hose is a LOT LESS so that isn't helping the cause either

gutting the cat will harm your performance due to less backpressure. this one is kinda iffy.
depending on what style of cat your cat has and how many of them gutting it might harm performance but not from lack of backpressure but rather more backpressure. then again it might help your performance out being the old cat was clogged or used a nasty restrictive style.
but what goes on when the air enters a hollowed cat? it acts as though it hits a brick wall a lot of times. that quick opening to the innard of a cat slows the air down. for the most part air is stagnent through there. another problem is the shape of a lot of cats create turbulance and eddies or other flow situations that make for resistance to flow. that stagnent air creates resistance for the next exhuast pulse to go through hence more backpressure.
now the catch that can make it worse or better then the cat itself is see even though gutting the cat creates backpressure it is a matter of does it create less backpressure then the old cats?




now on to the main portion as to why backpressure is BAD

two things I want to say real quick
there is two types of pressure I am going to be talking about

backpressure which is a resistance to flow. generally can be rated in PSI
and then we have Delta pressure which is the pressure difference between two points

another interesting thing talking about pressure is the faster an object moves the lower it's pressure internal pressure is. try putting the rounded side of a spoon under a faucet with the water running
why does the rounded edge cling the the water as strong as it can? the water is an area of low pressure and on the other side of the spoon is high pressure thereby making the spoon go to the water.

so to talk a little about scavenging here for a second
scavenging is using that delta pressure (delta P). as you should know if you put a zone of high pressure next to a low pressure zone the high pressure going to try to even out with the low pressure zone. the greater the difference the faster the exchange happens. the less restriction between the two spots the quicker it will try to equalize. your cylinder is one big mess of high pressure. and the lower the pressure inside the exhuast (header to catback) the greater the delta P (pressure difference) and what is going to do is get the exhuast pulse out into the exhuast with less pumping loss by the motor itself as well as create a vacuume inside the cylinder which is going to help draw the next intake pulse inside the cylinder to help better fill it with fresh air/fuel.
so you ask where does backpressure fit into all this? how shold it? backpressure is resistance in psi? if you want to get the greatest difference in pressure between the cylinder and exhuast system that would mean you want the lowest PSI in the exhuast system which means no backpressure.
another problem with backpressure on top of restricting flow and causing a lower pressure difference is that it can help cause reversion. now what is reversion? that is when the exhuat gasses change direction and head back towords the exhuast port. when you have high amounts of backpressure/low exhuast velocity your exhuast gas can be sucked back in once the piston passes TDC and is now heading back to BDC that creates a little low pressure zone inside the cylinder and having backpressure kinda reverses the whole delta P thing. and this burnt gas mixture is going to cause a problem with making for a cooler combustion. sure it might reduce NOx but heat from a hotter combustion makes for more pressure. burnt gas will cool things down. also it can mess with the flame front. creatin an irregular burn.
also comes the problem of pumping loss. if the exhuast pulses help one another to help suck the exhuast out it makes for less work for your motor to do. when there is backpressure again remember that is resistance to flow that means your motor is also overcomming that resistance. that means WASTED power.

so let me ask this question real quick also. what woud happen if I could turn your exhuast into the freest flowing thing out there and figure out a theoretical fan to put on there. that would cause a vacuume correct? vacuume means little to no pressure... hence no backpressure. and with the concepts we just talked about I'm sure you can imagine what would happen.

with pipe sizing. too large of a pipe will cause a restriction in flow just as too much of a pipe will.
sure the large pipe wll flow a lot more under static pressure flow.
but in a pulse system what is that the exhuast gasses start to eddie around and more or less just flow in random patterns also leading to possible reversion. all of these cause restriction.... BACKPRESSURE.


small pipe we all know aobut.
chockes the living **** out of your car right?
we can pass that one then

another thing to think about is sonic tuning
makenzie71 kinda touched up on it but here I can go a little more in depth for you.
first backpressure doesn't cause pressure waves that bounce to and from the exhuast port
those are caused by changes in elasticity of the air.
you exhuast pulse starts out as a high pressure pulse hits a big open area like a gutted cat. that sends back a negative pressure pulse (not exhuast gas just a pressure/sound pulse) to the port.
if this pulse hits the port when the valve is open it will reduce the pressure in the exhuast and make the gas come out faster and easier (another clue that backpressure is BAD). things that cause these waves?
youe tail pipe, collector, gutted cats, mufflers can be a smalle cause of them. basicly anything that changes the shape, size or flow character of the exhuast gasses. now sure most of them do cause backpressure but some can relive or keep it the same...

now problem is it only works for a small narrow rpm range.. and at some rpms ranges it can make a high pressure zone right in front of the exhuast port and do more harm then good.

and now to kinda address the turbo crowd
this will be small though
but some people are saying that scavenging has no effect on a turbo car.
those people are worng also
before the turbo you can't really controll too much without different style turbo so the pressure there is kinda win/lose situation

but what you can do is make it to on the part after the turbo (d/p back) is as low pressure as possible. what this will do is help scavange the exhuast from the turbo system even and make the turbo spool quicker, flow more. should be able to figure that out from the topics we just talked about


might add more later
my fingers are getting tired and I'm bored so off to something else now

Originally posted by Air_Adam
And why would anyone say that hp goes up and torque DOWN? you need need to create torque to create horsepower...

Originally posted by bonz
Maybe not on V8s but on the little honda's and other 4 banger import crap taking away back pressure will burn out your engine quicker.

Originally posted by bonz
Maybe not on V8s but on the little honda's and other 4 banger import crap taking away back pressure will burn out your engine quicker.

Originally posted by txhotRS
YOU NEED A LITTLE BACKPRESSURE FOR LOW-END... but there are always high-flow cat's for that

Originally posted by iroczman380
WTF???????

YOU PEOPLE JUST DONT GET IT DO YA, NO BACKPRESSURE IS NEEDED, NONE!!!!!! BACKPRESSURE IS BAD, WTF DOES IT TAKE.