Exactly, and N2O is a positive pressure enviornment.
Also, 3" piping is way too big for the output of the TC. Unless the car is being force fed the car will lose some neccessary backpreesure (read: torque; which is more important than HP) and the exhaust will most likely unload during decelleration and make a super annoying popping noise in your pipe right before the muffler. It sounds like crap. I would recommend 2.5" tops for a single exit catback. Unless you're pushing a lot more power or ripping it to 9K RPMs you'll be more than happy with the 2.5".

 

whatever noob. I admitted my mistake.

 

ntirous is still a power adder, so you cannot run in any "allmotor" class with it. its an oxydizing gas, therefore bringing more fuel/air into the combustion chamber is defined as forced performance. n2o is in no way "forced induction" but it deters you from defining yourself as allmotor either. no air pressure is created with n2o, so the motor still aspirates itself via intake/port/valve yadda yadda.
X-eric-X

 

More dis-information.

No car needs or wants backpressure. And there is no universe where backpressure equals torque. The goal of an exaust system is to remove exaust gasses from the piston chambers as quickly and efficiently as possible. On an NA motor there is a little bit of tuning that helps accomplish this. One of the things people do is increase the size of their exaust tubing. More room = quicker gas removal, right? Well, up to a point. You see... exaust gasses are hot. Hot gas is less 'heavy' and more difficult to move than cold dense gas. When you go to a large diameter exaust 3"+ the gasses cool in the pipe and become more dense and less easy for the motor to push out. Hence a bigger pipe can equal MORE backpressure.

This is not so important in a forced induction motor, because you have a giant air-pump (read supercharger/turbocharger) that is basically using brute force to accomplish what we are trying to finesse out of a NA motor.

Forced induction = 'force inducing' (pushing) air into the motor at higher than atmospheric pressure, generally with an air pump operated by the crank (supercharger) or exaust gasses (turbo charger).

Naturally Aspirated = Allowing the motor to 'aspirate' (breathe) at normal atmospheric pressure.

 

i got custom 2.5" piping from the cat to the axel-back. took the resonator out and it sounds nice and deep. not ricey and raspy. i paid $60 - $80.

 

3" is waaay to big for N/A!!! 3" exhaust is really needed for the 3xx + hp F/I cars.

For even mildly modded cars (only I/H/E) 2.25" exhausts have also proven to be real good upgrade...2.5" have been real good for the stock S/C ppl and even ppls with a turbo kit such as the stage 0..

And yes a turbocharger/supercharger may be using brute force to force air into the motor, but it DOES need backpressure or else you will lose boost, remember a turbocharger works on exhaust gases....

And essentially you would like hotter gases traveliing through the exhaust due to hotter gases flow much easier that cooler denser air

 

anyone who beleive 3" inch exhuast is good for an NA tc should be shot..

and scion speed is a joke!... lol.. another thread were to many stupid ppl posting crap misleading others.. what a suprise.

and caveman is correct in his words...

2.25 or 2.5 is ideal for NA tc.. 2.25 would be optimum.. but 2.5 is ehh ok.. anything more and your jus making a fart can louder

 

I found this post looking for exhaust answers. I have an AEM CAI, DC headers, and a Greddy SP2 Axel Back exhaust. I wanted to know what to do witth the rest of the exhaust(headers to axel). I have heard about different S-pipes and mid pipes that are pre-fabed and sold but I have also heard that these bottle neck at the ends. Would custom be the way to go? Should i replace everything from the headers back or are there some stock peices i need to leave in place. Keep in mind that I live in KY where there are no emissions tests anymore.

Thanks for any help

 

Get a turbo, then you can say 3" will be optimal. Otherwise you're just making room for air that the engine can't create. You might as well just put a 6" pipe on it if you think bigger is better.

 

If I only had the money :D