3 inch pipeing for exhaust bad idea ?

[wrx!kid]

iam going to be makeing my own exhaust soon for my 08 wrx 4 door

i want to have 3 inch pipe from the cat to the rear axles and from the axles split into two 2 1/2 pipes to mufflers

my question is do you guys think the 3 inch pipeing is overkill ?
should i just keep it all 2 1/5 inch ?
and would it be dumn if i used only one muffler ?
it would save me about 12 pounds if i only used one muffler

[snicker]

I would figure 3" w/ one outlet would be the best choice, exhaust gaes wouldn't change direction there by providing stable "path" for quick exit. I'm no scentist though

[wrx!kid]

cool thanks for your input

[strat]

alot of guys run 3" exhausts (myself included) on the 02-07 wrx's do I don't think it would be overkill...

i'd prob stick with one muffler though.

[anaonbd]

There is a point I've heard at which you actually lose torque because of lack of back pressure with larger diametre pipes. My VW was a good example, it was a 2.0 and was told by other VWvortex members and mechanics that a 2 1/4 pipe is the biggest I wanted to go without sacrificing torque.

[wrx!kid]

thanks guys for all your input i have decided to go with 2 1/2 piping,one muffler and no resanator i have most of it tac welded together i will finish up in the morning

[JustyMan]

well you have a wrx? with a turbo.. less back pressure the better.. to an extent.. look at all those after market turbo back exhausts, they are 3" all the way back!

the race exhaust system like the Tanabe G spec is 3" no cats no resonators to a N1 style straight thru exhaust.. soo i dont think it matters when u have a turbo

[me_jimmy]

in my opinion 3" is sold because it is allot "cooler" i read somewhere that 2.5" is enough for 300hp

[wrx!kid]

well i ran out of argon gas on my tig welder so i cant finish it so right now i am rockin a straight pipe 2 1/5 catback exhaust its not that loud to be honest
i read on NASIOC that its bad to run a straight pipe because it messes with the AFR's or something what do you guys think

[wrx!kid]

in my opinion 3" is sold because it is allot "cooler" i read somewhere that 2.5" is enough for 300hp
yea i read this to

if yourmaking well over 300+ HP then a 3 inch is better

[KevinWelker]

3" is fine for any turbo Subaru application. If there is no turbo 2.5" is more optimal. Fewer bends, lighter weight and less mufflers is always a good idea.

[aresbykes]

i'd go 3" with a turbo. less backpressure = more power with a turboz

[saturn]

yeah big pipe forcing you to lose torque only applies to N/A engines. your turbo creates all the backpressure you'll need :)

so yeah 3" will work... just depends how you want it to act/sound.

me personally, I'm doing 3" pipe from the DP to the catback, then probably some sort of Nurspec or something rumbly like that. right now I have a 2.75" pipe replacing the muffler and it's pretty decently loud.

[RA Limited]

well yeah it's going to be quiet if you still have the stock downpipe and cat. I have fully open turbo-back on my RA, and it's loud as crap.

[saturn]

I have stock downpipe (with cats) and stock midpipe (with resonator) to a straight pipe... basically I don't have a muffler

it's rumbly and makes a sort of WOOOOSH sound at WOT

here's a video:

http://www.youtube.com/watch?v=qZ0lyvOWK5c

[RA Limited]

saturn, the setup you described would possibly only be rumbly, and barely rumbly at that. Stock DP's and cats are very restrictive and i can't imagine your setup being much louder than stock (i can't view youtube at work).

[saturn]

right, it's not nearly as rumbly as full turboback exhausts... but it's rumbly considering it's just a pipe replacing the muffler.

I was mainly trying to show it'll have a weird WOOSH vs. a louder rumble at WOT... so it may not be what the OP is looking for.

[wrx!kid]

yea iam not sure whats up with that woosh you have going on

[tsidreams]

I say keep the duel exhaust, and no muflers. ;)

A smaller exhaust might give a little more spool up, but a bigger 3" will give you more top end out of the turbo.

my $.02

[pomspeed]

I already run a 3" cat back on an 04 STi. Since I still have stock exhaust cat forward the back pressure restriction still exists. I went 3" to simplify and lighten the exhaust.

So, yeah you'll be fine if you finish the project 3" cat back single exhaust.

BTW, I have a flowmaster "muffler". It reads 103db thankfully, I haven't yet been pulled over for noise.

[RanchoRat]

About the AFR, by eliminating cats, you change the AFR and by doing that, your car isnt running correctly. you need to go get a tune or get an access port and tune your AFR back to what your car requires.

[saturn]

I have a full 4" now with tons of torque -- it all depends on how you tune the car.

[impreza_GC8]

OP, there's a reason nearly every aftermarket exhaust for the WRX is 3" in diameter. You should do a 3" exhaust to gain power, its a no-brainer. When it comes to turbo vehicles a simpler and larger diameter exhaust will get you the most power.

[saturn]

yeah. the piping leading up to the turbo creates all of the backpressure you'd need in a turbo engine... after the turbo, the least restrictive airflow is best for power. the only reason most people don't go above 3" is there isn't room for it.

look at semi trucks -- they use piping up to 6"!

[RanchoRat]

DAMN SON 4" hows that sounding? catted?

[saturn]

no cats, just a high flow resonator and apexi N1 copy, I made a thread here about it:

http://www.dirtyimpreza.com/forums/showthread.php?t=9761

[RanchoRat]

:headbang:siiiiiick!

[azchris]

watching your vid makes me mad that i live in Arizona. they have no rally x like that here. well at least i cant find any. i want to go rally xing.