I have a 99eclipse gst with 16g 550's 255pump and fmic i need to know what is better for my car a 2.5" exhaust or a 3"exhaust or 2.5 downpipe and 3" catback??

I would vote a 2.5 to 3 inch downpipe, highflow cat, and a 3 inch cat back.

When it comes to exhaust systems on turbocharged vehicles, bigger is better. If you can put a 3" turboback on it, it will be much happier than a 2.5".

it really depends how much hp you are going for. I have read that it really depend on what your goal is with your car, if your going for high number 3" is better since better flow but also i have read that if your going for decent amount of hp you could good with 2.5". Correct me if i'm wrong tho

But i'm going to be using same setup as you but i'm going with 3" since i will upgrade turbo later on to push more hp.

talongod said:

I have a 99eclipse gst with 16g 550's 255pump and fmic i need to know what is better for my car a 2.5" exhaust or a 3"exhaust or 2.5 downpipe and 3" catback??

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with your current setup, it doesn't matter 2.5 or 3. But, if (when) you decide to start upgrading you will need to get 3". I was just like you (and many more)... I had gotten 2.5 because it was enough for what I needed at the time, started getting bigger power, and had to upgrade to 3". Now I need to upgrade my injectors... it's a vicious cycle of upgrades. You can end it now for your exhaust if you just get the 3" from the start. Go with a magnaflow muffler and you won't have to worry about it being too loud. My 3" w/ magnaflow is just as quiet as my 2.5" w/ magnaflow.

It will depend on some factors, First is money of course. Second is hp goal you will be looking for. I mean a 2.5" exhaust will be fine for 350-375 even 400 whp. But, as most people will keep modding there cars you will normally gain more hp and then may need to switch out to a larger 3" system. So, if you only have limited funds a 2.5 would be sufficient but, if you have alittle extra dinero you might as well just go with a 3".

vr4play said:

I was just like you (and many more)... I had gotten 2.5 because it was enough for what I needed at the time, started getting bigger power, and had to upgrade to 3". Now I need to upgrade my injectors... it's a vicious cycle of upgrades. You can end it now for your exhaust if you just get the 3" from the start.

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Amen to that!!!!!

It's a real pain in the ass when "enough for what I needed at the time" is over. You actually wind up losing money that way. Personally, whatever your goal is hp wise, I say add another 100hp to that. From there, that's how I would decide what parts to buy. If I woulda realized that when this project first started 3 years ago...........

Who makes a good **cheap** downpipe for the 2g gsx that doesn't eliminate the cat. I'd like to go megan for the "bang for buck", but I don't want to get rid of my cat all together

TSIMonsteR said:

Who makes a good **cheap** downpipe for the 2g gsx that doesn't eliminate the cat. I'd like to go megan for the "bang for buck", but I don't want to get rid of my cat all together

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Its probably easier to buy one that DOES eliminate the cat, then have a high flow cat of the same size welded in. Thats what i did on my car after researching the same exact thing as you. My whole exhaust only cost me like 600 bucks installed, full 3 inch. Of course they were all bought off of ebay, i made sure the catback was a real bosal.

TSIMonsteR said:

Who makes a good **cheap** downpipe for the 2g gsx that doesn't eliminate the cat. I'd like to go megan for the "bang for buck", but I don't want to get rid of my cat all together

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www.roadraceengineering.com makes downpipes and cats that bolt up to the Apex'i N1 exhaust systems.

It is important to note that Apex'i and RRE downpipes are not true 3" downpipes. They are 2.5" before the flex and then expand to 3" after the flex. If you have a 2G o2 housing or any other o2 housing, it is normally 2.5", I don't see why have a 3" downpipe opening at the o2 is so important and needed, but I'm sure other members will disagree.

All I'm gonna say is that even though it takes awhile to get parts from them. rnr racing makes a 3.5" system that will flow enough cfm's to support 37 psi from a gt42r and a 100 shot direct port system. If you require more then that God be with you when you pilot your car. Available for 1g and 2g awd's only. Prices start at $899 for downpipe and downpipe to muffler.

www.rnrracing.com

-----Jace

TSisleeper said:

All I'm gonna say is that even though it takes awhile to get parts from them. rnr racing makes a 3.5" system that will flow enough cfm's to support 37 psi from a gt42r and a 100 shot direct port system. If you require more then that God be with you when you pilot your car. Available for 1g and 2g awd's only. Prices start at $899 for downpipe and downpipe to muffler.

www.rnrracing.com

-----Jace

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If I may ask why would you recommend a 3.5" exhaust to someone who has a limited amount of modifications. I am not trying to be rude. Also why would you recomend this for someone who has a fwd knowing that they only sell these for an awd 1G and 2G?

Could you imagine a FWD that required a 3-1/2" exhaust? It would probably just boil the tires off.

NickatBuschurs said:

I also do not see where they make a 3.5" fwd turbo back exhuast.

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I've not seen one either.

If you decide to go with a 3" setup, make sure you port the 16G for boost creep before you bolt everything back on.

GSntncT said:

I've not seen one either.

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This is because they are for awd's.

go with a 2.5"-3" downpipe and a 3" catback.

NickatBuschurs said:

If I may ask why would you recommend a 3.5" exhaust to someone who has a limited amount of modifications. I am not trying to be rude. Also why would you recomend this for someone who has a fwd knowing that they only sell these for an awd 1G and 2G?

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Do you think using a 3" exhaust on a 400whp car would signigicantly lower backpressure over a 2.5" exhaust?

If you have the money, might as well go with the 3"...take your car to a muffler shop & have them make you a custom turboback, if you can. I bought a Megan Downpipe on Ebay for 110 bucks & took it to them, they installed it along with the rest of the exhaust they made. I'm sure they could've even made me a custom downpipe also. It's just piping with a flex section, so even then I probably could've saved more. I see no reason for people to spend 600 or even 500 bucks on an exhaust system. Total I paid for mine was $310. ($200 for Magnaflow muffler & 3" piping, $110 for downpipe...no cat)

I did't take it as you being rude "nickatbuschurs" I was reading 2 different posts and posted this thinking I was on the other one, sorry about that, my mistake. I'd say 3" for your application too brother.

vr4play said:

it doesn't matter 2.5 or 3.

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Not true. With a 3" there will be less back pressure because of the increase in piping diameter size (reduces the friction factor) which will effect the behavior of your turbo, no matter how small or big the turbo is.

TSisleeper said:

All I'm gonna say is that even though it takes awhile to get parts from them. rnr racing makes a 3.5" system that will flow enough cfm's to support 37 psi

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As to why anyone would ever recommend purchasing parts from RnR is beyond my comprehension. The business practices of RnR should be enough to stray anyone away from them.

GVR4592 said:

Do you think using a 3" exhaust on a 400whp car would signigicantly lower backpressure over a 2.5" exhaust?

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I'll try to run the theoretical numbers next week and see what it comes out to be.

I don't believe 3" is overkill for anyone. 3" will yield more power even on a 14b than a 2.5" would.

It also depends on power goals, future turbo goals, ect. But i recommend 3" to just about everyone, just because these cars are like crack to mod. You start little, and you end up building up a 2.4 stroker running a gt42r, with a full race TRE tranny and no interior.

Anyway, go 3" man. Sounds mean, has excellent flow, and will support anything you wanna throw at it later.

I picked up a consistent 1.2-1.3 lb/min of airflow (roughly 13 h.p.) from midrange to redline switching from a 2.5" to a 3" catback setup. Difference is very noticeable as the acceleration is much more violent. I wouldn't recommend a 2.5" to anybody. Noise levels are really good if you run some kind of resonator or midpipe muffler setup. I'm probably running 300-310 w.h.p. and saw a good difference, YMMV.