I'm currently running a 2 1/4" piping with straight pipe custom exhaust and I like how quiet it is especially when I'm boosting. I was thinking of getting a bolt-on catback (greddy, hks, etc). How much HP or how much better airflow would I be getting from a 3" exhaust? I know it will probably be louder than my custom exhaust but are the gains worth sacrificing quietness and discreetness? I know there are a lot of quiet catbacks out there like RSR and Tanabe...what would be best for the OZ Rally?

 

greddy is pretty popular, I am running magnaflow and love it. How much are you boosting? If you are running low boost (5-6 PSI) I would say your exhaust is fine and you would only gain 1 or 2 HP from going that much bigger. 2.5" would be the biggest a boosted lancer would need anyway so you MIGHT lose a little low end from the 3". If it were me I would save my money and invest in something else.

 

disregard didnt read you were turboed, i just woke up k...

+1 on Druceas post

 

Don't waste your money on the heavy aftermarket catback, just have a shop make you a custom 3 inch. The only thing I'd spend money on is a good muffler, that is what will be seen and change the sound as well. Magnaflow and GReddy are both good. But I think 3 inches will help a lot more than a quarter inch. It more depends on you other mods. Do you have just a turbo, or do you have the intake manifold and throttle body ported or anything else?

 

You don't have to worry backpressure with a turbo. 3 inches will be fine. But with NA, backpressure could be a problem.

 

The car is at 8psi with stock internals. I just wanted to go 3" all the way b/c that's how big my DP is. Also, my exhaust is pretty old; it has rusts spots and leaks I patched up w/ JB weld That's why I'm thinking of just getting a bolt-on. Is there a big difference in performance if I upgraded to 3"?

 

If you go ahead and get it now, it will be better for the future. On stock internals and 8psi, it isn't really needed, but if your current one is rusting, might as well replace it now at a bigger size.

 

As far as bolt ons go, I can't think of any that are 3". Greddy and Magnaflow are 2.25" and I think the JIC is 2.5" although it may just be 2.25" as well. I can't think of any other legitimate catback exhausts (ie. not ebay exclusives) for the lancer, so if anyone knows of any feel free to pipe up. I'm not sure how much you'd gain since no has ever done a before and after dyno for this kind of this. I can't see it hurting though. As Drucea said your best bet is to get a custom setup made. Make sure it's stainless steel and mandrel bent (very important) with no or very little bends in it. For a muffler just go with whatever style or company you prefer. I have a greddy catback and the sound is great, so I would assume a catback made with the same muffler would be close in sound as well.
Edit: Found three more catback exhaust systems, DC Sports, Thermal and Vibrant.

 

I say get a custom catback made to avoid paying $700 for the stainless steel. Why do you need stainless? It's way heavier and no one is going to see it.

 

It really depends where you live, Aluminum mufflers will rust.

A lot of chop shops do crush bending, so 3" would have same flow as 2.5-2.75" on the bends.

 

Well I don't think I really have to worry about Aluminum b/c theres no snow and salt here during the winter. But I will consider the 3" custom exhaust; it does sound like it will be cheaper than a $600 brand name bolt-on. How many resonators should I run to keep it quiet?

 

I would just run a cusom 3 inch exhaust with a high flow cat (or test pipe) and a good name brand muffler. Would probably come out to around $400 including the cat and good muffler. Cheap when compared to a $700 magnaflow catback that no one will even see.

 

I would strongly recommend you get something like stainless steel or some other rust-proof metal. Obviously not being exposed to snow and salt is a big plus, but don't forget about rain and just general pollution (which dissolves in rain and acts as a corrosive agent). As for a resonator, don't bother, the turbo should keep it quiet.

 

I'd say go to a shop, far cheaper then a catback. I've never had an exhaust from a shop by me last less then 4 years. And I live in an area that has way too much salt put down then needed.

 

Shops also usually don't do stainless, and I think the price of the first exhaust, then even if it rusts, it will be cheaper than stainless. But I see you live in SC, the ocean water might have an effect on rust as well. So do what you feel like doing, either way it should turn out good.