Disadvantages of 3" exhaust?

[2016 Camaro SS]

You will notice a loss at low rpms with a 3" exhaust. 3" isn't even necessary unless you are going for 500 whp. Just excessive noise/rasp, weight, and cost.

[johan]

Size isn't everything when it comes to exhaust flow. Most OEM cat backs are very low restriction in this day and age... they have to be - with all of the emissions crap they have to deal with on cars now, the engines wouldn't make much power if the exhaust wasn't free flowing.

Case in point, on my 2011 Civic Si, with a Kraftwerks kit, I made 410 to the wheels on E85, running high 11's in the 1/4 mile with the stock header / exhaust and a high flow cat. Obviously this is no Honda engine, but it's generally accepted that a supercharged engine doesn't gain much from exhaust changes. I actually changed to a 3" at one point on my car and made almost no additional power (yes I retuned).

Now on a turbo'd car, it's a different story...

[Poodles]

Backpressure is a myth.


Regardless, a 3" catback isn't going to do much outside of being loud. It's the rest of the exhaust in front of the catback that changes the powerband.


Supercharger isn't going to make the exhaust any less loud either. If anything, it would make it even louder. Exhaust flow also isn't as critical on a SC setup vs turbo.


If you were going turbo it would be totally different.

[KoolBRZ]

Originally Posted by Poodles

Backpressure is a myth.


Regardless, a 3" catback isn't going to do much outside of being loud. It's the rest of the exhaust in front of the catback that changes the powerband.


Supercharger isn't going to make the exhaust any less loud either. If anything, it would make it even louder. Exhaust flow also isn't as critical on a SC setup vs turbo.


If you were going turbo it would be totally different.

Just get a smaller equal-length header, upgrade the over-pipe to at least 2.5", keep the catted front pipe, stock rear pipe and upgrade to a decent axle-back muffler. I have a Top speed Pro 1 header, axle-back muffler, 2.5" over-pipe, and an OFT for tuning. I just took off my 2.5" catless front-pipe and reinstalled the stock catted front pipe. Now I'm making more power and better MPG. It may not be all about the back-pressure, but low-end power is all about exhaust scavenging and tuning.

[sw20kosh]

Forget anything anyone told you about 'back-pressure is good for torque'.

[cdrazic93]

Oh man if I had a nickel for every thread I've read...

[omfg5041]

Actually, too much back pressure and you can cause ping/detonation. Too little back pressure, you're going to lose power, and poor engine performance. Ideal back pressure is about 1.25-1.75 psi in an exhaust.

[stockysnail]

My tuner slapped on my innovate w/ intercooler and 70mm pulley with my JDL UEL catless headers, Nameless 2.5 OP/DP resonated/catted, stock midpipe, and nameless 2.5 w/ 5" mufflers. I got about 250whp. He slapped on the complete AVO 3" to the JDL header and he got about 20whp more, so in my experience the 3" got more power. However the setup (nameless I mentioned) was a little too loud going up the long hill I had to go up every day so I took off the stock midpipe and nameless axle back and put on a Nvidia Q300 instead, which makes hills ok to drive up again without being too loud. The car is still loud when giving it a healthy dose of pedal, but when not on it I get a slightly louder than stock noise. The nameless does sound better however, but I couldn't take the hills anymore.

One advantage of an exhaust that's not overly loud is I can hear my supercharger whine much easier now, which is more fun hearing anyway.

[Captain Snooze]

Originally Posted by omfg5041

Actually, too much back pressure and you can cause ping/detonation. Too little back pressure, you're going to lose power, and poor engine performance. Ideal back pressure is about 1.25-1.75 psi in an exhaust.

Could you point me in the direction of articles that would explain these concepts?

Originally Posted by omfg5041

Ideal back pressure is about 1.25-1.75 psi in an exhaust.

What is the difference between pressure and "back pressure"?

[omfg5041]

Originally Posted by Captain Snooze

Could you point me in the direction of articles that would explain these concepts?


What is the difference between pressure and "back pressure"?

Sorry for the delay in my answer. The term "exhaust back pressure" is a term used in the automotive industry. It is essentially, the pressure opposed to the desired flow of fluid in a confined area. In this case the exhaust gases in the exhaust pipe.

Now to explain. Exhaust gas is a hot gas as we all know. If there is a build up of pressure caused by the exhaust pipe, the exhaust gasses cannot escape quick enough to keep the exhaust cool enough, therefor building up heat in the exhaust manifold and inside the cylinders. As such, the potential of overheating and causing ping/detonation, or the engine computer will try and compensate with timing to reduce temperatures. Doing so, will reduce the power output as it working on keeping temperatures down.

That is what we learned in college when we went over catalytic converters and exhausts. If you have any additional information, please explain. I am more than happy to be corrected if I am wrong.

[Captain Snooze]

*sigh*

[Xinshadow]

Its not so much pressure, its velocity. The exhaust pulses have a scavenging effect, meaning they help suck spent air out of the cylinder and fresh air into it. Make the pipe too big, and the speed of the gas slows down, lessening the effect. The reason a larger exhaust is beneficial to a turbo is due to the lager amount of gas created (more compressed air/fuel), a larger exit helps ensure a better scavenging effect so the engine can breathe correctly. SCs benefit less because boost is lower, less gas created.

This is just a quick explainer and nowhere near 100% complete, but just a general overview, this does come up a lot haha

[Calum]

Originally Posted by omfg5041

Sorry for the delay in my answer. The term "exhaust back pressure" is a term used in the automotive industry. It is essentially, the pressure opposed to the desired flow of fluid in a confined area. In this case the exhaust gases in the exhaust pipe.

Now to explain. Exhaust gas is a hot gas as we all know. If there is a build up of pressure caused by the exhaust pipe, the exhaust gasses cannot escape quick enough to keep the exhaust cool enough, therefor building up heat in the exhaust manifold and inside the cylinders. As such, the potential of overheating and causing ping/detonation, or the engine computer will try and compensate with timing to reduce temperatures. Doing so, will reduce the power output as it working on keeping temperatures down.

That is what we learned in college when we went over catalytic converters and exhausts. If you have any additional information, please explain. I am more than happy to be corrected if I am wrong.

Don't egr systems reduce cylinder temps?

[Calum]

http://www.gomog.com/allmorgan/exhaustbackpressure.html