will a 2.5 exhaust be fine or 3 in exhaust be better?

[wishful_laser]

i am going to get my exhaust done this week and i need to know if i should get a 2.5 in or 3 in exhaust. i want a 3in stainless but the its kinda pricey. i am looking at 2.5 aluminized right now. bad choice or should i just save my money and get the 3in stainless. i need some advice. oh, i have 1g fwd too. i wanted an apexi but they do not make one for my car.

 

[HokieDSM]

I'd say it depends on your goals. I'd definitely go with stainless though, and mandrel bent isn't even a question. I've got a 2.5" - and the previous owner used the same 2.5" with an FP Green turbo and was running 11s on it - so it can definitely do plenty well, but 3" will give you faster response in theory along with more room to breathe if you've got big plans.

But if you don't plan on taking it far from stock, I'd say 2.5" would do well enough.

 

[Laser93Nash]

2.5" should be good like HokieDSM said. Especially if you go with an o2 dump.

~Andrew~

 

[wolfes_dsm]

like hokieDsm said "it depends on your goals" i would say get 3" s/s because thats the best you can get and u wont have to upgrade it at all down the road if u need it, and if price is a matter then think about if your going to have the car for a long time or not, if your not going to have the car for very lone then u wont have to go with s/s but if u plan on having the car for a long time then save up and get the s/s

hope that helped, jason

 

[CowPimp]

Go with 2.5" if you care about noise; go with 3" if you don't. 2.5" will get you into the 11s if you want to, but a bigger exhaust on a turbo car still means lower and faster spooling. I'm perfectly satisfied with my 2.5" exhaust, but there is no reason not to go with 3" other than noise. Go an O2 eliminator downpipe though, definitely. It made a huge difference on my car.

Aluminum is fine. Aluminum exhausts will last 10+ years. I have a feeling you won't be keeping your car longer than that. Stainless steel certainly looks better though.

 

[blcknspo0ln]

just get 3" and be done with it. you wont notice a difference between the two. except the LOUDNESS

 

[philipkrotch]

just get the 3"...also, there was quite a few threads about this that u can find if u search for em.

 

[c5chris]

I would say 2.5" if you decide to upgrade to a T28/Big T28 or a 16G/Big 16G Turbo.
If your plans include a 20G, 50 trim or bigger turbos then the choice would be a 3".
My only concern with a 3" would be noise and resonance. For a daily driver, those low frequencies day in and day out will make you go deaf or desensitized to low frequencies. Plus, cops will pull you over more often with a loud exhaust.

Just my $.02

 

[blcknspo0ln]

2.5" or 3" you're going to get noticed anyway.. so mind as well get the 3" in case you upgrade down the line [ i know i will be going 50 trim by the end of the summer ] . just search and you'll find your answer

 

[TurboBird]

I have heard..... don't quote me or anything but I have heard that 2.5" will flow better than 3". If you read most tuning guides they say you don't even need 3", http://www.buschurracing.com/stage_1.html, I am not sure about this though, but it makes sence.

 

[mitsuclipsegsx]

3inch

 

[blcknspo0ln]

i'm sure bushur racing has it's reasons to say that a 2.5" will flow more than a 3".. but just take a second and think about that...

willa 2.5" hose flow more water than a 3" hose? i think not.

 

[HSK]

not trying to jack the thread, but i think it would be helpful if someone could cover the noise lvl dif btwn the 2.5 & 3 in more detail - i.e.: is the noise lvl significantly different?

far as picking the size of piping - there are some n/a with 2.5 piping (i know some vtecs w/em)... so i guess it would be nice to have a 3" with a turbo setup. if you are concerned w/loudness, use a resonator and a quiet exhaust.

also is your car lowered? do you have plans on getting it lowered?
if yes, i think a 3" piping can't go over the rear axle like stock and 2.5 can, so its going to under the axle (someone correct me if im wrong.. has anyone managed to put an 3" over the axle?)

bottom line 3"piping under axle + lowered car = pipe scratching/denting.

 

[c5chris]

My 98 GSX's stock piping runs under the axle. I thing all GSXs have this route in their stock exhausts.

 

[leet]

i'm sure bushur racing has it's reasons to say that a 2.5" will flow more than a 3".. but just take a second and think about that...

willa 2.5" hose flow more water than a 3" hose? i think not.

You can fit a gallon of water in roughly 3.9 feet of 2.5" pipe.

You can fit a gallon of water in roughly 2.75 feet of 3" pipe.

(Atmospheric pressure)

Keep in mind that is merely a demonstration of volume. Other things will affect your actual exhaust flow rate(bends, velocity of exiting gasses, etc.)

 

[blcknspo0ln]

all else equal then you're numbers are correct. but yea, 2.5" or 3" should be fine either way

 

[95GSXBLUR]

be careful with a 3" depending on what you go you could end up with boost creep.. i'm going a 2.5 dp & cat to a 3" cat back. i'm pretty sure that set up can handle like 400whp ish.. just a thought.

 

[SpoolnTsi]

I agree with Buschur Racing with the 2.5" exhaust. But it also depends on what kind of mods you are running, what your goals are and most importantly the turbo. It also depends on if you want fast spool up time but less top end or if you want turbo lag but excellent top end. If your running and evo 16g is smaller, a 3" exhaust will induce lag but you will have good top end. 3" exhaust is more for bigger turbos like 20g's and up, but like i said it all depends on what u want. Think about it, its the same as hooking a hose up to a water hydrent. If you hook a 1" hose up and a 2" hose up to the same hydrent, which one is going to flow better? There both flowing the same amount of water but one of them is going to throw the water further and faster. The 1" hose will. Dont believe me.................try it! Sometimes bigger is not always better(depending on what ur running). As for the noise level, that all depends on what type of muffler u get. Good luck with your dsm project

Oh yea, im running 2.5 on my car now with a 16g and it pulls hard all the way to 7000 and spool up starting at 2600 no BS

 

[wishful_laser]

thanx for all the info guys. i think i know what i want now. i am going to get it lowered and i do plan on getting an agp 50 trim around christmas.

 

[98RedGs]

thanx for all the info guys. i think i know what i want now. i am going to get it lowered and i do plan on getting an agp 50 trim around christmas.

That's going to depend on your roads and stuff in your area.
Good roads?
Bad Roads?
Big potholes?
Big speedbumps?

If yes to any of them (2-4) then you would want to consider a 2.5 if your lowering your car a great amount. But the 50trim will breathe nicely with the 3inch if that's what your 110% sure your going to be getting.

 

[CowPimp]

If your running and evo 16g is smaller, a 3" exhaust will induce lag but you will have good top end. 3" exhaust is more for bigger turbos like 20g's and up, but like i said it all depends on what u want.

Nonsense. A bigger exhaust means less turbo lag and faster spoolup because turbochargers are powered by exhaust gases. The best exhaust for a turbo car is an open exhaust.

 

[leet]

Nonsense. A bigger exhaust means less turbo lag and faster spoolup because turbochargers are powered by exhaust gases. The best exhaust for a turbo car is an open exhaust.

Agreed. Exhaust systems don't generally cause creep, insufficiently sized wastegates cause creep.

 

[SpoolnTsi]

For 20g's and up yes that will help with spool up, but not for 16g's and smaller. 3" on 16g's and smaller is too much unless your going for topend. it will create backpressure and lag on low end

 

[mitsuclipsegsx]

what about a 3inch DP, would that cause boost creep?

 

[icedearth15]

Check out my mods on my car, I used to run a 2.5" exhaust press bent, I moved to a custom 3" three bend exhaust system and the car runs alot better, quicker spool, better pull. You dont need a huge turbo to take advantage of a bigger exhaust, and even feel a nice difference between the two. I would just do 3" , and never look back--there is no reason for a three inch exhaust to hang any lower than any other part of your car......the noise, well if you want performance you are, in alot of cases going to have to deal with it, bottom line is if your going to put down your hard earned cash on something do it right the first time. In the end its up to you, but thats my experience.