3.4 2.25" vs. 2.5" exhaust
 

After all the issues I have had with my headers and exhaust I finally take it to an exhaust shop that has a focus on custom exhaust set ups. As loud as Angel has been, I could have sworn there was another leak or something not welded/fastened properly.

Nope. Apparently it was all good. The only thing making it sound like I had no exhaust, was the size of my exhaust (2.5" pacesetter catback). It was also stuck against some things it was not supposed to be touching and put together in a crude fashion. They said they were going to move it around so it would not touch in places it should not, but instead they ran a new 2.25" piping to my pacesetter muffler/tips.

One of reddogs posts says the 2.5" is what works best for our cars. The shop owner says that 2.25" is more than enough for the HP the aleros have. The 2.25" is quieter but still sends enough flow to provide the rumbles I like from my pacesetter muffler. However, I can feel more back pressure from the gas and such.

Does the .25" make that much difference-other than the loudness I was not a fan of.

The pacesetter headers provide enough extra flow to turn the 2.5 into the loud monster from the muffler-rumble only with the stock headers.

One important thing is the type of bends used. Mandrel bends are what you want, to maintain a constant radius and smooth flow at the bend. So 2.25 mandrel bent may even be better than 2.5 crush-bent. But 2.25 crush-bent is not acceptable with the headers.

As the exhaust gas flows toward the back of the car, it cools and its volume decreases, so it might be acceptable to start with 2.5 near the headers, but go to 2.25 further downstream. Transitions from large to small should be as gradual as possible, at least a 4 to 1 (of the pipe diameter difference) ratio is recommended.

Do not go from large to small then back to large in the transitions either, flow loss results in each change of radius. A possible exception to that is at the muffler itself or resonator if you use one. Easiest and probably best would have a constant radius throughout the system.

Usually, but not always, higher flow systems are louder.

Interesting concept. Essentially 100% of the shops, engine builders, and other performance enthusiasts I've ever talked to or researched are under the impression that if you must use different sizes, increase the diameter as it gets further down the line.

Well, we're talking a very small difference in size here, and basically what is acceptable in his case. I am sure increase is better than decrease for an all-out build. Tuning effects from the length of pipe come into play, placement of components for sound control.

I think I would give up a little flow to get rid of the drone sound inside the car. Almost every exhaust shop mechanic that drives it says "That's pretty loud."

I can feel a difference on the gas between the two sizes though. Is there a way to keep the 2.5" and decrease the drone? Different mufflers maybe? Dampeners?

The exhaust guy had said he has a car with 400+ hp with only a 2.5" pipe so the 2.25 is more than enough for my car...at that point they had already changed the diameter. I was under the impression they would just tweak some things to my 2.5.

And that is exactly what happened. If it is a mandrel bend it will be completely smooth on the outside even when bent and such right?

And I intend to get the engine tuned, are you saying this will have some effects on that?

Yup, perfectly smooth all the way through. Myself, Id work with the 2.5" and maybe try a different muffler on it. If you ever decide to get into internals in your build, you'll be glad you did because your going to end up ripping it all out for a 2.5" anyway man... just my 2-cnts

I prefer 3" with a race muffler and high flow cat......:scpimp:

But in reality try a magnaflow street series muffler, they tend to be a lot quieter than flowermaster, slp, or any other crap.

I saw flowmaster makes a new pipe called the Hushpower muffler. I would leave your current setup as it and install the long hushpower muffler inline after your cat (like a resonator)

Should make a big difference......

Did you listen to the video I posted in the "Sound of headers" thread?
That exhaust is 2.5" all the way from the headrs, with a cat, Magnflow resonator and cross-flow muffler. Most people from the board would say that it's pretty tame.

yes it is pretty tame Matt...

http://www.youtube.com/watch?v=YHDL8QPqI1U

http://www.youtube.com/watch?v=SeEpPYQSVPQ

You guys let me know what you think. This is with the new 2.25 in there.

What is irritating is that the shop put in the 2.25 without asking me about changing size first...so now I have to go back and get 2.5 put back in.

Kwhauck, is this hushpower muffler a muffler or an actual 2.5" pipe I can run back from the cat? Or is it just an add on to muffle pipe noise?

The only thing that was too loud was the pipe noise itself. Drowned out the nice muffler sound and everything else. Made a pretty bad cabin drone-made me feel like I was driving a piece of crap vs. something that had a performance mod.

It is an actual muffler, but the ones i've seen are small enough it could easily fit inline in the exhaust tunnel before the exhaust turns in front of the gas tank....

Doesn't seem too loud to me.
My Malibu with a 2.5 cat back to a magnaflow muffler (no res, in hindsight I wish I did) is much louder:

http://www.streetfire.net/video/2001...ck_2294693.htm

http://www.streetfire.net/video/2001...mh_2298544.htm

That's with a ported UIM & 65mm TB as well, although I'm not convinced that those contribute to noise aside from a whistle.

I have a Magnaflow 2.25 system on mine and Love it. I can have a conversation inside my car to my passenger without having to yell!

Different strokes for.... you know...lol Mines loud enough that I have to shut it down in some drive-throughs because the poor girls working can't hear me over the car!! I still love the sound of this cam even after six years

Those videos are with the 2.25 exhaust, not the 2.5. Without the headers, my exhaust sound was perfect. Put the headers on and the extra air flow made it loud...

What other mods do you have? Eventually I will begin the mod the engine which means I will need that 2.5 back. I like the quietness of the 2.25 but I would rather have the feel of the 2.5 but with some way to reduce the sound a little bit.

Ya that didnt seem to loud to me, I have a 2.4 5speed (i know they sound different then you 3.4 guys) but I found mine to be a tad bit loud so what I did was use a Hushpower muffler from flowmaster insted of a res, and i used a hushpower crossflow muffler and it seems to be the best combo I have found. It has almost no drone on the highway, but when you get on her you can still tell its not a stock exhaust note. Go on the flowmaster website and check them out, I really like the sound mine gave me.

Alright first off....GET ON THE DAMN THING....when you were driving in the car you were going slower than my Mom. I wanna hear this thing OPENED UP....not just short little revs....damn. lol