# 3" vs. 2.5" Catback.. **URL:** \ **Category:** SON240sx Automotive\ **Created:** [August 25, 2004, 11:00am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480 "2004-08-25T11:00:54Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![nocwage](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/nocwage/32/5489_2.png) [@nocwage](https://forums.speedlife.net/u/nocwage)\ **Post date:** [August 25, 2004, 11:00am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/1 "2004-08-25T11:00:54Z")
I don’t plan on running 400hp on the CA, so should I bother with 3" catback? I’m going to have a 3" DP to a 3" cat. And then I figure 2.5" from the cat to a 2.5" muffler. Should I go all the way to a 3" or is there no real point? ---
**Author:** ![s14\_2Nv](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/s14_2nv/32/5476_2.png) [@s14\_2Nv](https://forums.speedlife.net/u/s14_2Nv)\ **Post date:** [August 25, 2004, 11:12am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/2 "2004-08-25T11:12:13Z")
3" exaust be better regardless of the amount of hp you are planning on running. ---
**Author:** ![SHIFT\_KA24DET](https://avatars.discourse-cdn.com/v4/letter/s/b9bd4f/32.png) [@SHIFT\_KA24DET](https://forums.speedlife.net/u/SHIFT_KA24DET)\ **Post date:** [August 25, 2004, 11:40am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/3 "2004-08-25T11:40:24Z")
> [@s14\_2Nv](#): > > 3" exaust be better regardless of the amount of hp you are planning on running. Agreed… N/A or Turbo it will give you better responce and better numbers. Thing is though if you are looking for something quiet and streetable go with a 2.5" Mike on this board has a CA with a 2.5" exhaust and his car is quick as a whip and is quiet as one too. ---
**Author:** ![MrSkinny](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@MrSkinny](https://forums.speedlife.net/u/MrSkinny)\ **Post date:** [August 25, 2004, 11:49am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/4 "2004-08-25T11:49:17Z")
ive got 3 inch with a silencer and its relatively tame ---
**Author:** ![SHIFT\_KA24DET](https://avatars.discourse-cdn.com/v4/letter/s/b9bd4f/32.png) [@SHIFT\_KA24DET](https://forums.speedlife.net/u/SHIFT_KA24DET)\ **Post date:** [August 25, 2004, 11:50am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/5 "2004-08-25T11:50:43Z")
> [@MrSkinny](#): > > ive got 3 inch with a silencer and its relatively tame With a Silencer it’s not a true 3" then. It acts as like a 1.5" ---
**Author:** ![s14\_2Nv](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/s14_2nv/32/5476_2.png) [@s14\_2Nv](https://forums.speedlife.net/u/s14_2Nv)\ **Post date:** [August 25, 2004, 11:51am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/6 "2004-08-25T11:51:47Z")
I would go 3" but it is up to you, with 2.5" you will be losing some power, but if you decide to go that route, I will have a 2.5" inlet dtm muffler for sale in about a month. ---
**Author:** ![MrSkinny](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@MrSkinny](https://forums.speedlife.net/u/MrSkinny)\ **Post date:** [August 25, 2004, 11:53am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/7 "2004-08-25T11:53:29Z")
yah but at least i have the option to whip it off whenever i want. for daily commuting i’ll have it on but when i have the urge… i jst unscrew the thing and let it rip ---
**Author:** ![nocwage](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/nocwage/32/5489_2.png) [@nocwage](https://forums.speedlife.net/u/nocwage)\ **Post date:** [August 25, 2004, 1:00pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/8 "2004-08-25T13:00:46Z")
Looks like i might as well go with the 2.5" for now, if I get the urge I just have to replace the cat-back anyway. I’d rather not draw a lot of attention 😉 ---
**Author:** ![s14\_2Nv](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/s14_2nv/32/5476_2.png) [@s14\_2Nv](https://forums.speedlife.net/u/s14_2Nv)\ **Post date:** [August 25, 2004, 1:06pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/9 "2004-08-25T13:06:27Z")
> [@nocwage](#): > > Looks like i might as well go with the 2.5" for now, if I get the urge I just have to replace the cat-back anyway. I’d rather not draw a lot of attention 😉 Well good luck not drawing a lot of attention with a right hand drive car. ---
**Author:** ![nocwage](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/nocwage/32/5489_2.png) [@nocwage](https://forums.speedlife.net/u/nocwage)\ **Post date:** [August 25, 2004, 1:10pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/10 "2004-08-25T13:10:42Z")
That’s not the kind of attention i’m trying to avoid 😉 ---
**Author:** ![DTS](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@DTS](https://forums.speedlife.net/u/DTS)\ **Post date:** [August 25, 2004, 4:19pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/11 "2004-08-25T16:19:41Z")
stop being a baby. the difference between a 2.5 and 3" catback on a turbo car is minimal, get a apexi exhaust and it will be uber quiet because of the massive resonator, and youll get better hp. Adam , N/A cars wit 3" exhausts dont always get better numbers because they need some backpressure or else you get shit torque. almost all mustangs run 2.5 max. ---
**Author:** ![SHIFT\_KA24DET](https://avatars.discourse-cdn.com/v4/letter/s/b9bd4f/32.png) [@SHIFT\_KA24DET](https://forums.speedlife.net/u/SHIFT_KA24DET)\ **Post date:** [August 25, 2004, 5:03pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/12 "2004-08-25T17:03:54Z")
> [@DTS](#): > > almost all mustangs run 2.5 max. Yeah Dual 2.5" I gained 15hp with my GP sports Exhust… ---
**Author:** ![s14\_2Nv](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/s14_2nv/32/5476_2.png) [@s14\_2Nv](https://forums.speedlife.net/u/s14_2Nv)\ **Post date:** [August 26, 2004, 6:03am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/13 "2004-08-26T06:03:01Z")
2.5" would be ideal for me on an n/a ka. Turbo car gains would be better with 3" exaust. ---
**Author:** ![MrSkinny](https://avatars.discourse-cdn.com/v4/letter/m/59ef9b/32.png) [@MrSkinny](https://forums.speedlife.net/u/MrSkinny)\ **Post date:** [August 26, 2004, 6:22am UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/14 "2004-08-26T06:22:49Z")
if you’ve got turbo dreams, might as well do it right the first time and go 3 ---
**Author:** ![santas](https://avatars.discourse-cdn.com/v4/letter/s/f9ae1b/32.png) [@santas](https://forums.speedlife.net/u/santas)\ **Post date:** [August 26, 2004, 2:38pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/15 "2004-08-26T14:38:24Z")
I’ve been told that 2.5 is better if you are going to stay NA while 3 would be choice for forced induction… i’m no mechanic tho ---
**Author:** ![jjm\_240sx](https://avatars.discourse-cdn.com/v4/letter/j/b77776/32.png) [@jjm\_240sx](https://forums.speedlife.net/u/jjm_240sx)\ **Post date:** [August 27, 2004, 12:38pm UTC](https://forums.speedlife.net/t/3-vs-2-5-catback/81480/16 "2004-08-27T12:38:01Z")
With forced induction bigger is better. You can run with out an exhaust at all to make the best power for forced induction. Why you ask? Because you don’t need any back pressure. All your back pressure is at the manifold to turbo inlet. For a N/A car you want about 3psi (i think its psi) of back pressure so that you can have your low end power. If you were to open it up you would have bad low end power but still good high end. didnt spell cheak this.