2.5" vs. 3" exhaust

[mcsmokey]

I'm getting ready to buy a cat back system for my frs. I've been looking at the Greddy Evo Gt. I was also looking at the Perrin cat back system but I think it's just too quiet considering I currently don't plan on doing anything else with the exhaust. I'm just wondering has anybody had any issues running a 3" cat back system on N/A motor or could I expect any issues to arise?

[Detroiter]

I have the Greddy Revolution RS 3" single exit and the only down side I can note is that it is very loud. I don't know how the Evo GT will compare but mine has plenty of drone and noise to make someone sensitive to it very annoyed.

If you plan on keeping the car N/A then I would choose a 2.5" system as the 3" would be overkill and potentially lead to losses. I think I remember a thread saying a Greddy 3" exhaust showed losses vs the stock system.

[smg1138]

Unless you want to add a turbo or supercharger later, I'd stick with a 2.5" exhaust. A 3" exhaust would be crazy loud and wouldn't net you any performance gains. Also, if you don't plan to change the headers, the non-resonated Perrin catback should be perfect. It only gets raspy if you combine it with catless headers.

[KnightRyderx2]

It really wouldn't hurt anything to run either. The only time is when you go FI you want a 3". So if the exhaust you want only comes in 3", that is perfect fine.

[DirtySouth86]

A 3" cat-back should not cause any real issues, but is not really needed. A full 3" exhaust on a NA car would cause a loss of low end power/torque and that is definitely not what this car needs. I also own a built 2003 Mazdaspeed Protégé. When I put the 3" turbo-back exhaust on it, I definitely lost some low end power and torque. It did gain more than it lost, but only at full boost and high rpms.

[Timmy_Jones]

3" exhaust on our cars, have consistently shown a SLIGHT increase in power. See the research that reputable companies like Perrin have done. These gains increase as you add mods and go forced induction. I would go bigger than 2.5" if possible (some of the companies make smaller exhausts) I believe the Invidia Q300 is actually a 2.3" setup. Not much gained over stock. I have a 'cheap eBay' setup which is 2.75" Inner Diameter and its really loud, really cheap and looks great.

[CypriniousM]

Currently running the 3" Perrin resonated catback, with no other mods (don't have the money to buy them yet) it's a great system with a deep sound with the stock parts. I heard the rasp of the non resonated version and didn't like it. There's a lot of rumble with the Perrin and you won't be sorry that you bought it. That hard part comes when your trying to find a used 3" front pipe and overpipe and realize no one ever sells them so you have to buy new.

When you get on it you definitely hear the exhaust but you don't get to drone when your just cruising.


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[GsxrMe]

Fullblown offers 3" overpipe back. Its also 3" vbands all the way back. I think cost was $1800 ish +/-. I dont remember the exact price I paid. I believe you can also get or request a resonator to be installed for you NA guys. You can get single exit or dual exit.

[Matt@Cosworth]

our testing showed a small advantage of about 3bhp of 3" vs 2.5" but as said it is a lot louder so you then need larger silencers

[wparsons]

Originally Posted by DirtySouth86

A 3" cat-back should not cause any real issues, but is not really needed. A full 3" exhaust on a NA car would cause a loss of low end power/torque and that is definitely not what this car needs. I also own a built 2003 Mazdaspeed Protégé. When I put the 3" turbo-back exhaust on it, I definitely lost some low end power and torque. It did gain more than it lost, but only at full boost and high rpms.

You can't really compare turbo to N/A cars when it comes to exhaust setups...

I'm a bit surprised going to a bigger cat back on your turbo car caused a power loss though, if anything it should've helped it spool earlier.