Problems with custom exhuast
 

First the setup:

88 CRX DX Chassis w/ DOHC ZC motor
DC Sports 4-2-1 Header
2.5" crush bent pipe (all welded)
Walker 3 way Cat
Flowtech Red Hots Glass Pack Mufflers (http://www.jegs.com/p/Flowtech/887185/10002/-1)
Magnaflow Performance Satin Stainless Steel Mufflers (http://www.jegs.com/p/Magnaflow/751042/10002/-1)


Now, the issues:

The car is currently in the prep stages for a junk yard T25 turbo kit. I opted for a louder, more freely flowing exhaust than I would tolerate on an N/A setup. Trouble is, it's really loud. There's a small drone while cruising, and a nasty vibration that only seems to occur at 1500-2000 RPMs during cruise or engine braking. It also has a bit of that ricer raspy sound.


The questions:

Does the muffling effect of a turbocharger have a reasonable chance of fixing any of these issues?

If the turbo won't have an effect, how can I improve the design to eliminate the low RPM vibration?


Useless reflection:

My best guess is that the glasspack is the problem. After failing to find a reasonably priced normal resonator, I assumed glasspacks were more or less the same thing. Maybe there's a difference between resonators and glasspack "mufflers".

Re: Problems with custom exhuast
 

Resonator vs. glasspack:
A resonator is a perforated (or louvered) tube inside of an expansion chamber using wave reflection for sound reduction.
A glasspack makes use of fiberglass baffling to (in theory) absorb sound.

I can't speak on the muffling qualities of a turbo, never had one.

I do have a car using no resonator, and only glasspacks. 4-1 header, high flow cat, glasspack, split, glasspack, then tips, on a 1.5 liter. It rumbles (incredibly too) but without the drone commonly associated with unmuffled small engines. So, I don't think its the fault of the glasspack.

Since you state the drone is in a small RPM range, try using a quarter wave resonator. They provide volume reduction at a fixed frequency, so tune to the middle of the RPM range that you have drone.

Bad example, but I can't find a better pic on Google. The upper pipe is closed. It simply provides a place for the sound to bounce back. No exhaust gas flows through it.
http://image.highperformancepontiac....to+exhaust.jpg

Re: Problems with custom exhuast
 

Ok, found better pics of a quarter wave resonator.

http://i51.photobucket.com/albums/f3...sE92M3002c.jpg

Just a capped off tube connected to the exhaust pipe.

Re: Problems with custom exhuast
 

Thank you for the feedback, I removed the comment about glasspack use being insane on the part the owner.

So the difference between a glasspack and resonator is simply the use of packing material behind the perforated/louvered core?

The method of eliminating the vibration is exactly what I was looking for. I figured it had something to do with pulse frequency, I just don't know enough about physics to figure it out myself. I think what you're using is called a reversion chamber, but I could be wrong. You mentioned tuning it for the specific frequency/RPM, is this tuning just a matter of trial and error with the length of the pipe or is there a better approach?

Re: Problems with custom exhuast
 

Sounds like the glass packs are your issue....and if you think its bad now, just wait till they burn out....it'll be nothing but rice...

The turbo does perform some sound reduction, well I shouldn't say reduction, it changes the tone to a deeper rumble.....since its a junkyard setup and your trying to save some dough, put the turbo on and see what it sounds like, if you dont like it, then worry about changing it

Re: Problems with custom exhuast
 

Well, my car is well above 92db (legal limit) at WOT, so in a way they are insane to use as the only form of muffling on a street car.

Its very very loud, but it doesn't drone or have a raspy sound, which is why I think they function as "acceptable" resonators.

Since you have a muffler in addition to the glasspack, it isn't so insane.

And srmofo is right, if/when they "blow out" you'll have an echo chamber instead of a glasspack. You'll hear it going, the sound will get louder over time, and you might see nice burning fiberglass strands come out of the exhaust while driving.

I think mine have only lasted because a 3" exhaust on a 1.5 liter that doesn't rev past 6k is completely overkill.

Re: Problems with custom exhuast
 

I got a hold of a physics major buddy of mine and discussed the vibration issue. We concluded that the turbo will likely take care of it.

If the turbo doesn't take care of the loud issue though, what kind of solutions can should I look at to quiet things down and eliminate some of the droning? The muffler is a free flowing perforated core, perhaps moving to a more conventional muffler will cost some flow but take care of it?

Re: Problems with custom exhuast
 

In all honesty, since you have crush bent pipe and its a JY setup, your probaly not pushing that much power to worry about the flow being restricted by a regular muffler...I would try a more convientional resonator first, and see what that does for ya