blueLScobalt

have a pacesetter exhaust on my 2.2....and i notice that it has alot of back pressure. i know that back pressure is goin to occur but it seems to be alot. i am just curious if anyone else is experiencing this and if you found a way to stop it. also if you have a pacesetter header with your exhaust....how much did it change the sound....good or bad

rally

I do not own the exhaust setup but planned on getting it at some point. The cobalt I noticed from the factory had a great deal of back pressure. The Pacesetter will likely have a lot of pressure also by the design of the system, back pressure is not a bad thing, you need it no matter what, you do not want to eliminate it.

nomoreavril

how can you tell it has backpressure? you dont need back pressure, you need exhaust velocity. the bigger pipe you get, the more freely your exhaust flow, but also the slower it goes. you want to get in the middle..so it flows freely, but not slowly. too big and it flows too slow, too small(stock) flows fast, but is bottlenecked. if you want an example, get a straw, and breath into it, and put your hand at the end. see how fast it flows out? now get a paper towel cardboard tube, and breath the same amount of air to it with your hand next to it, see how you can barely feel it? hypothetically, if you had 100% backpressure, or whatever, it would reverse the flow back into your engine, which would not be good.

halfj99

"if you had 100% backpressure, or whatever, it would reverse the flow back into your engine, which would not be good."

well unless he welds a metal plate over the end oh his exhause, this isnt happening

Halfcent

Im curious too. How exactly do you know there is a lot of backpressure? Do you have a pressure gauge connected to it or something. It wouldn't be something you can feel. What makes you say this?

HunterKiller89

iTrader: (1)

...why does the rate at which it flows matter? so much as a large enough volume of gasses are flowing out...
think about it...everyone needs to breathe atleast X amount...so whats it matter if your breathing through a stawor just your mouth so long as your still getting the same number of breaths per minute and those breaths all are full breaths

as for 100%..that would ean nothing is moving, it would have to be >100% to flow backwards

1SloBowtie

Exhaust is just like waste, get it out faster, it'll perform better...

06cobaltls

i think i will run 5 inch from the header back, i bet that would look cool, not to be a noob, but can someone explain the reason that you need some back pressure, or why you dont need it, i have heard from somewhere that to big without backpressure can hurt your hp, but i cant remember, and also wit aftermarket mufflers, they give you a silencer and say that when you have that in it gives you better low end torque, is this true?

en0onmai

More Back Pressure = More low end torque. The silencer slides a tube halfway into the muffler and restricts the flow a little bit. I had an Apex'i Canister with the silencer you mention. When the silencer was in I felt a HUGE diff in power off the line. Not as much top end but a TON from dead stop to 2500 rpm. Take the silencer out and LOTS of noise but the butt-dyno felt the gain in mid-top range. Anything 4000 rpm and above. Right now I am running a 2.25" mandrel bent setup to a magna flow straight through muffler. Sounds great, loss of a little off the line power and lots of mid-top range. No more downshifting on the freeway to pass. Just ease into the throttle and away I go.

sushidog

The benefits of back pressure is a myth. It doesn't add torque, it reduces it. What does add torque is scavenging.

You see, the exhaust gasses exit your exhaust pipe as a series of pulses created when the cylinders fire in sequence. Place your hand behind your exhaust and you'll see what I mean.

As the pressure pulses travel down the pipe they produce a high pressure wave in front and a negative pressure wave behind. If the exhaust is sized correctly, the negative pressure pules from one cylinder draw the high pressure pulse from the next cylinder along with it. This is called scavenging. Think of it like drafting in Nascar. Too low of a velocity resulting from too large of a diameter pipe will reduce the scavenging effect, thus reducing torque. Allowing the exhaust gasses to cool will also reduce exhaust velocity and torque. This is why ceramic coating headers, and/or wrapping exhaust pipes often helps power.

IonNinja

changed the sound to poo

if you don't mean hearing the exhaust flow through the header then it won't bother you but my exhaust sounded much cleaner without the sound of sand rushing through my exhaust.

en0onmai

But wrapping headers also can keep too much heat in resulting in weakening of the metal and possible cracks in the piping. This has been reported by quite a few distributors. One of the reasons my headers cracked on my Prelude too! Heat wrapping headers = bad. Now ceramic ones are cool! or Hot or whatever! Never thought of wrapping the exhaust piping though. Doesn't NASCAR use oval piping? Maybe just a myth but hey! who knows?

sushidog

Good point. Never wrap headers! They will hold too much heat causing metal fatigue.

Wrapping is often used in offroad racing. It stops water splashed on the exhaust from excessively cooling the exhaust gasses. For street vehicles, it can help to maintain exhaust velocity for long runs of oversized pipe. For instance, a 2.25" exhaust is probably the ideal size for our n/a engines to promote the scavenging effect. However, a 2.5" will offer less back pressure and thus produce more torque - if the exhaust gasses don't cool too much and slow down before they exit. Insulating the exhaust will help to keep the exhaust gasses moving.

This is especially important if you have a turbo-back system. I polished and chrome plated a turbo housing once on a motorcycle to help hold in the heat, promoting efficiency.