i was talking to this guy today and i told him i got the header and all and i said something bout getting a high flow cat, and he told me that if i do that my car will slow down even more becuase i will loose compression and back pressure off the motor..... i was arguing becuase why would they make high flow cats if they make you go slower?? just let me know whats up

Because highflow cats were designed for turbo cars where they don't want any restrictions.

NA cars need some back pressure, and eliminating the cats (or installing a header and high flow cat) will severely drop the back pressure.

Turbo engines don't need back pressure.

ok what do you all think i should do? leave the stock cat on and do a 2.5 inch ex all the way back or leave the cat on and stock exaust and just put the header on?? im not for sure what to do

I/H/E for best results. Why open up the beginning of the exhaust flow if you're keep the end restricted? See what i mean?

O.k., someone who knows this topic really well...What is the ideal exhaust setup for the different engines in the 3g?Most HP/Torque benefits come from doing what to each one?Sore subject in the past but I personally dont know cause I havent tried them all.

i don't know if Rob will agree with this, but as it is. any naturally aspirated vehicle due to the nature of the fuel injection needs some type of back pressure.(and if you think a turbo car doesn't have back pressure you do more drugs than i do, i'll talk about it later and you will see) this way your car doesn't dump needed residual air, even if it is part exhaust. a free floating air system will dump out needed exhaust, it then adds more pure oxygen into your system which ends up making your car run lean. basically what it does is the normal amount of air sucks into your cylinder, but is a more concentrated air mixture than optimum. if your MAS was some how hooked into your exhaust to change your fuel output from there it might be good. but since there is just a emissions sensor telling your ECU there is something wrong, it tends to just keep running like crap.

i know people say the more the air the more the power. this is true, but only when thinking in terms of air traveling through your MAS, not through your exhaust. lean air/fuel mixture is good for economy driving, but bad for power. the amount of HP lose may not even be noticeable to some people, but people who like to have fun in their cars like me or race on highways and run high RPM and high speeds may notice it.

when you have a turbo you not only have back pressure, but you will have more back pressure than a N/A vehicle. whatever psi setting you use for your wastegate thats the amount of pressure that is needed to push your turbo as fast as it does. turbo cars have lots of back pressure, lots. once out of the exhaust port on your turbo there is no more need for back pressure, in fact back pressure after a turbo is not good. this will cause that ever so famous glowing turbo that racers hate to see.

the reason for letting the exhaust escape as quickly as possible after your turbo is a issue of both easy air flow, and turbo cooling. when someone has a turbo you can have as big of an exhaust as you want, no catalytic converters, and no muffler. the reason why people use both is due to law requirements. which is why people get high flow cats(some people buy these and then cut out the insides, straight through mufflers,(some people just use resonating tubes for their mufflers instead), and wide band O2 sensors(these will read your O2 levels without the back pressure the OEM ones settings are set to). ask any racing mechanic. as soon as your exhaust gets through your turbo and the sooner it dissipates, the lower the temperature your turbo will operate at.

in conclusion:
back pressure after turbo = bad operating temperature for turbo
back pressure on N/A motor = Good due to emission controls
N/A system with set of headers and stock cat = no real change
free flowing exhaust after turbo = Good for keeping turbo at lower temperatures
free flowing exhaust on N/A motor = bad, emission controls don't read correctly and change ECU settings.

you can however dump your back pressure after the cat, but other than for maybe 1 HP to the wheels and a lot of noise, why pay $250-$325 for it? i can see why people buy intakes, there are specific reasons why and also other things you can adjust, bypass, or remove to make your intake worth about 10-15 HP, too bad most people don't know the race secrets. anybody can try to pick my post apart, i may even be wrong in certain instances, but i have researched most of this myself and i can tell you that the subject of which i state is true.

if you want a decent sounding exhaust for super cheap.
(remember guys i am fully saying this is a cheap as **** mod i know it may not suit a lot of the deeper pocket guys)

find your local laws on exhaust positioning if legal, cut your exhaust and run it out in front of your back tire with a glass pack. (don't go psycho on me yet guys) before you put your glass pack on get a hand torch, a welding glove, and a long set of pliers. put on the glove and grab the glass pack with the pliers. heat your glass pack up so its bright red all around it. then throw it forcefully down into a bucket of water thats only 2 1/2 inches deep this will shatter the glass inside the muffler. now cool it down and shake as much glass out of it as you can. now repeat the process. once this has been done weld it onto your custom exhaust you made to point towards just before the front of your back tire. your exhaust will have a incredible roar and it will only cost you about 30 bucks. once the glass pack is on it will be straight pipe, but look like it has a muffler. no emission shop has caught this mod yet and i have done it on 5 of my own cars. i no longer do it, but i have deeper pockets now.

All you need to do is read this article.

http://www.mitsubishi-forums.com/t30665-ex...really-need.htm