Anyone running 3" exhaust & catless header?
 

Hello all,

I was thinking of going to a full 3" exhaust with a cat-less header and catted front pipe. Anyone running a set up like this?

If so, what kind of layout are you running in terms of mufflers and resonators? What kind of sound levels are you getting?

Please comment on your setup and post vids!

Thanks!

Are you planning on forced induction??? 3" is a little much N/A Im at 2 and 1/4

yup make sure you're not losing any back pressure with the 3inch either.

No forced induction, its for an STX car where every little bit helps.

I'm not a fan of most 2.5" systems since most use the factory donut gasket for the cat-back which still pinches down to 2.25". The only true 2.5" exhaust that I'm aware of is the Perrin that uses a chamber style muffler, which I'm also not a fan of.

I'm not sure I want any back pressure, maybe you're talking about harmonics for the scavenging effect?

you want back pressure for an na car.

think the back pressure is where you're getting some of the torque from. if you lose back pressure, you might actually experience a lower torque or throttle response

Some back pressure for a FI car is good too! My Grand Prix was supercharged and when I ran open headers I lost a lot of back pressure and lost a lot of launching power ( which was good, I would spin off the line like crazy) but I had more top end power. I would stick with the 2.5 like everyone. Gotta figure I am sure GReddy and other billion dollar exhaust companies know better than you.

this engine will make far more power on a 3 inch vs. 2.5 inch all day. try it before you knock it. remember... this engine is at 12.5 compression.

Although this is turning into a great discussion about exhaust system design principles, lets get back on topic and hear from people running this set-up!

well sir 1.) show me proof and 2.) why arent all the top companies making there exhaust systems that wide then if its supposedly better???

I can answer #2. NVH and cost. Not everyone has a racecar. These companies are first and foremost a business looking to make a profit, so having a modular system that is compatible with the stock system opens you up to a wider customer base but still leaves you with its deficiencies. Not to mention the higher cost to produce bigger system.

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Found this on a high performance shop website specifically talking about the FRS/BRZ


I will mainly leave my car stock or add slight modifications. What exhaust do you recommend?
If you are going to mainly have a stock car with the exception of an intake and various other modifications, you can simply get a new axleback or catback exhaust that is around the stock size or a bit bigger. We don't recommend to go with too big of an exhaust as you won't gain much power but you will certainly create a lot of noise. At these kind of modification levels, a nice 2.5" exhaust would be just right.
I want to get a full exhaust, all the bolt ons, and maybe later nitrous or a supercharger
If you know you are going to try and make more power with all of the bolt on modifications plus a power adder such as nitrous or a supercharger (note we're not grouping turbo kits into this), then we would recommend at least a 2.5" exhaust or more, maybe even a 2.75" exhaust. We also recommend an exhaust that has a straight through muffler for less restriction. A straight through muffler will be louder, but also allow you to make more power as the muffler isn't as restrictive and allows for easier exhaust flow.
I need power! I am going to go turbo for sure, and need to make as much power as possible
For the all out exhaust, we recommend a 3" exhaust with a straight through muffler as well as the rest of the exhaust also being upgraded with 3" from the turbo back. If you are going to run less than 10 PSI, you can still run a 2.5" or 2.75" exhaust, but you will limit your power potential. For those with a built motor, 3" is the way to go.

I have a 3" header back exhaust and catless UEL header. I seemed to have more power than others were making (after tune) with the 2.5.

and that's exactly the setup I had, OP, that with an Injen intake, was making 200whp NA.

I personally wouldn't go 3 on a NA motor. My Mustang has 2.75 and it is a lot more responsive than when it had 3's. I'm not planning to race my FR-S at the moment, but I think I'd be more than happy with a 2.5 exhaust and supporting mods.