Rep Power: 310

running rich is worse for emissions and better for power and engine operation.

emissions: lean is better because Complete combustion is hard to achieve and so putting less fuel makes the mixture burn easier and burn more complete reducing hc's (hydrocarbons), therfore less raw fuel is put into the air and clogging the cat converter, however tooo lean and the air will heat up so much coming out the engine that it will increas noX emissions which is also bad.

Power: the gasoline is releasing the power of the engine with the strength of the explosion, more fuel will allow for a much more explosive combustion in the chamber and therefore release more power, taking away fuel (running lean) will not maximize the performance of the engine. (this is why high performance engines have bad mpg, not just displacement but the fuel ratio.

Engine operation: 14.7 is perfect, too lean and parts will heat up, you can melt holes in the pistons, heat up and melt/warp valves, cause overheating and lots more parts are effected and it will also cause preignition, not detonation but preignition. (there is a slight difference). running too rich can cause incomplete combustion and clogg the cat over time, cause tons of carbon deposits in the chamber and on the valves, these deposits can then heat up quick and cause hot spots causing detonation and poor air flow through intake and exhaust ports and through the chamber itself. both mixtures can foul spark plugs prematurely.
i think possibly you mistook lean for rich, for instance seeing a 16:1 thinking its rich when its lean and seeing a 12:1 thinking its lean not rich. alot of people do, i used to also.

 
Rep Power: 310

the popping you see and hear is when raw fuel comes through the exhaust with hot air and once it hits oxygen outside of the exhaust it explodes because its so hot. (needs oxygen for fire, we all know this right) any car even a lawnmower will "backfire" with exhaust off, what you did was remove the most crutial part, the catalytic converter, it has gold and other soft metals in it that heat up quick to ignite any raw fuel left in the exhaust air, so technically the cat causes "backfires" all the time however thats not technically a backfire, its just an explosion. the muffler is not there at all to muffle the sound of the loud pops, it is there to keep down the exhaust tone to be quiet although of course it does do it, thats not its point. also this is another reason that cats are in the middle of your system or in our case right at the engine. so that the fire from unburnt fuel has room to die down and/or burn any raw fuel around it and be gone by the end of the system as well as the sound. this is why a car with high flow cat or especially no cat will backfire like crazy driving anywhere, and youll actually see these explosions out the muffler.

a sidenote, some cats actually have a little fitting that uses fresh air from your intake and puts that into the cat so your exhaust has fresh oxygen to play around with and it will promote the explosion but at the same time this can cause higher noX emissions.

 
Rep Power: 0

hey, i have an idea how about you blow me you ***. did i ask your opinion on my stuff?? .. what do you have done to your car?? read my profile... my cars more modded than most on here... not all, but most...

 
Rep Power: 256

so is having (no cat) bad???

 
Rep Power: 812

bad for the environment and is illegal most places.

 
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depends on who you ask. no cat means less restriction in exhaust flow. more power. but yes depending on where you live its illegal. does your state or county require e check or any kind of emissions?

 
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i know that pop pop pop pop sound...my friends si does dat, his car is fine...i want dat pop pop pop pop pop pop on my auto LOL

 
Rep Power: 256

well it is illegal, but mostly the boys in blue around here wouldnt be that much of a D___k to give u a citation for one, unless your caught racing or doing stupid stuff on the street, than he'll probly check ur car out, and btw, my check engine light turned on after almost 2 day that i put the headers, my "mechanic" friend said its normal for the 01 LX, since the cat was on the manifold, he said the bottom sensor is reading differ air pressure, due to not having the cat on the header, so what do u guys think?

 
Rep Power: 310

then your mechanic doesnt know much, it would throw on a light because there is too much unburnt fuel and high emissions because the cat is gone, nothing to do with difference in air pressure. find a new mechanic

 
Rep Power: 256

well sorry, "I" kinda put the word air pressure in it, he told me something else which i totally forgot about, but yea, im pretty sure he said the same thing as u, but the point i was trying to make is that it comes on even though the sensors are put on too, only that the cat was on the manifold, and now its not

 
Rep Power: 310

so pretty much, you dont have a cat. thats the reason the light comes on. the sensors are built to read how bad the emissions is and there are limits for it until the computer puts a light on. the cat is what keeps the numbers within the limits so without it the light comes on. there are a few ways to fix that, search "02 sensor foulers" "02 sensor bypass" and remember to try that as 02 and o2

(this was typed in simple terms)

 
Rep Power: 256

thanks, i'll look for that

 
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your mechanic is right... on my 05 ex i have header, no cat, magnaflow cat back. i threw 6 diff codes. all about my oxygen sensor. pressure too low, lean in o2 bank. there was 6 diff codes, i put my cat on for a week and drove and didnt throw any code at all...