newbie exhaust questions...

[dosborn]

i've decided on a universal muffler, not sure which brand yet, for my 95 240.  i'm wanting to get the muffler shop to put some bigger pipes on it, too.  i have a few questions:
1.  what size pipe should i get?  2.25 or 2.5?  would 2.5 be too big, reduce low range torque?
2. would pipe size effect sound, loudness?  
3.  would i get a power increase if i just get rid of the cat altogether?  there aren't emission inspections here in arkansas.  would that effect sound any?  how?
sorry for all of the questions, but i just wanna be prepared and know exactly what i want.  thanks
derek

[jyt747]

I'm planning on doing the same as what you're going to do. 2.5 inches is a good size and from what I hear, the torque loss is very minimal and can't even be noticed. The pipe size would affect the loudness and if you don't want it to be too loud, you can get the apexi mufflers and ge a silencer for them. Getting rid of the cat should free up some power, but will be extremely loud. Could be wrong though, so get a second opinion. Hope this helps.

[tnord]

ideally we would have a pipe that is slightly smaller than 2.5in. coincidentally, 5Zigen makes an exhaust with that exact size. bigger pipe will make you're car louder. you might get a power gain from getting rid of the cat, but not much.  replacing with a pipe probably only reduces backpressure by about 10% resulting in about a 2hp gain; nothin to write home about.

[sykikchimp]

not to mention that the loss of back pressure from the dump pipe (cat replacement) would also cause another loss of torque.  Unless your turbo of course.

[sleepermode]

i think our cats have 2 sesors in them one coming in and one coming out. i think tkaing out the cat will mess up ur ecu

[LanceS13]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from sleepermode on 11:40 am on Mar. 1, 2002
i think our cats have 2 sesors in them one coming in and one coming out. i think tkaing out the cat will mess up ur ecu</td></tr></table><span id='postcolor'>
only on the '95+ OBDII 240's.

[tnord]

i've said it before and i'll say it again.....backpressure=low end power is a MYTH

[240sxspeedracer1]

so is it recommended to take out the cat?
Has anybody done that? &nbsp;I wanna replace my exhaust system as well and if I can add more HP I would, it would probably be cheaper casue hey would need to put in a cat.

[Ni5mo180SX]

Yea had the cat out on mine for awhile. Doesnt sound too good. Put one back on and it doesnt really make you lose too much power.

[gfisch]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from tnord on 3:34 pm on Mar. 1, 2002
i've said it before and i'll say it again.....backpressure=low end power is a MYTH
</td></tr></table><span id='postcolor'>

You definately lose a ton of torque when there is minimal back pressure.
I had to make a drive out to the hardware store to get bolts to put on my new exhaust after already pulling off the old one, and had much less torque off the line. It was almost hard to drive.

[White240sx]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">Quote: from gfisch on 9:47 pm on Mar. 1, 2002
You definately lose a ton of torque when there is minimal back pressure.
I had to make a drive out to the hardware store to get bolts to put on my new exhaust after already pulling off the old one, and had much less torque off the line. It was almost hard to drive.
</td></tr></table><span id='postcolor'>

Large diameter exhausts causes flow stagnation, especially on the low portion of the rpm range, because the gas velocity is decreased. Thus a too large exhaust will actually increase backpressure, which doesn't allow the cylinder to empty as much at the end of the exhaust stroke, which in turn lowers your VE, and thus the torque curve is negatively affected.

[dosborn]

the reason i asked about the cat is because it needs replaced. &nbsp;how much is it to replace? &nbsp;if it sounds better with the cat on there, it will be on there. &nbsp;i read somewhere about replacing the cat with a glass pack? &nbsp;is that a good idea?

[ant]

I have a '91, and the &quot;guts&quot; fell apart in my cat and cloged the exhaust. &nbsp;This had an extremly negative effect on the performance of the engine. &nbsp;However, after removing the debris, and reinstalling the factory exhaust, there was a noticable increase in power and a slight increase in volume.