throttle out

I've posted this in a couple of the Chevy truck forums and not gotten much so I figured I try this here.
I recently did an LS swap into my 87 K10 Chevy short bed. It's a 5.3 LM7 out of a 99 silverado.
I have Shoenfield long tube headers with 3" collector, 3" stainless ball flange into Magnaflow 12619 round straight through 3" mufflers. 3" stainless pipe fully tig welded save for the ball flange. If your standing at the door or laying underneath the truck there are no audible leaks, but when your standing behind it at idle it sounds like there is a leak coming out of the pipes. It has a low deep tone/rumble but there is a hiss/exhaust leak type sound mixed in as well and I cannot figure why. At WFO it has a good aggressive sound with a touch of crackle but I believe an H or X pipe will solve it. It has potential to sound awesome but it seams like I missed something with this setup. If anyone has any thoughts PLEASE share!!

Thanks Yall!!
Sammy

kswLS1

iTrader: (1)

Longtubes will have a crisp/sharp pop/hiss sound. The pop/hiss is due to the more breathable and audible longtubes versus the restrictive cast manifolds. However, you should be able to hear it all around the truck, not just behind the tip. Open the hood and see if you can hear the pop/hiss while idling.

throttle out

The air leak hissing type sound is most audible at idle.
Under the hood at idle it can be heard but the sound is most certainly coming out the back.

throttle out

Here is a little clip of of my exhaust. Not the best but the sound I'm trying to eliminate is easy to hear. Any help is greatly appreciated!!

CITY GARAGE

1 of the mufflers is installed backwards

throttle out

That's an interesting thought but they are straight through Magnaflows and can be intsalled in either direction. Both mufflers are also installed in the same direction.

CITY GARAGE

then they would both be installed backwards. seen this problem before. keep scratchin your head i guess. good luck

throttle out

I appreciate your input man. It clearly states on the boxes they came in and on Magnaflow's website that they are universal and can be installed in either direction. They are model #12619 and the muffler is perfectly symmetrical, there is no in/out.
May I ask about what you have seen before and what the sercumstances of that situation where by chance? Just curious what mufflers where used in the senerio.
I am intrigued by what your saying but hard to cut the system apart based on a thought that goes against what the manufacturer is telling me is all.
However I may vary well owe you a case a beer before its over.
Thanks man!

Full-Force

iTrader: (11)

Get those shitty clamps off and weld it up. Those clamps you have are made for butt joints. Look at the bracket cocked sideways on the clamp because you are using a butt clamp for a slip fit connection. At best that type of clamp is helping the pipes not pull apart but it does nothing to seal. Why anyone thinks that thin piece of metal is going to compress 16gauge pipe is beyond me.

If you want to use clamps then first prepare your pipe like the pipe in the pic, then use a clamp like pictured below.

throttle out

Thanks man.
The clamps were temporarily in place until I got my hitch mounted up so I could finish mock up and weld er up the rest of the way. I came home today and for ***** checked the clamps and they were loose as could be. Tightened them up and the sound is MUCH better! Gonna try to weld it up tomorrow. Thank you for your help, would not have though a leak at the very end of the system would be so prominent.

Full-Force

iTrader: (11)

I dont know if all of that funny sound is coming from the leaking clamps but I can tell you this for sure: A system put together with sub par clamps that have a little leak here and a little leak there vs a fully welded up system or a system with good clamps and no leaks is night and day difference in sound.

kinglt-1

iTrader: (26)

its a combination of LS motor and the muffler resonance.

throttle out

I welded up the rest of the exhaust the other night. Sounds better but still have some of that sound coming through. Thought it could be the ball flanges so I put silicone on those. but didn't make to much of a difference. I will say this, after a 20 minute drive to work, if I shut it off and fire it back up the noise is all but non existent and the noise is most prevalent on cold startup. If I lug the motor without causing a downshift, I can hear hissing like a leak would sound but at this point the only other place a leak could be coming from is at the header gasket at the head or the headers themselves are leaking. I still plan to ad an X-pipe to the system.
here's a quick sound clip after the clams were removed and finish welded.
www.youtube.com/watch?v=9o3vW9iWDT4

joyridin'

iTrader: (1)

I worked in an exhaust shop for years. Sounds like the resonance of the pipes being too big for the engine. We used to hear it all the time in Mustangs when guys put on 3" exhaust with basically stock engines. Some cars do it worse than others. Considering you have a truck with a lot of pipe and not a huge amount of bends, this could be the cause.

You do not mention a crossover pipe. Do you have one?

kinglt-1

iTrader: (26)

It is never going to go away completely...my car made a similar sound when cold after I put Kooks true dual exhaust on it. It is some kind of resonance...however it went away when I added H/C/I and upped the compression.

throttle out

No crossover pipe yet. Planning on an x-pipe.

throttle out

I went with the 3" pipe because I plan to do a cam, and twin turbos. Figured the 3" would be perfect at that point. Had no idea it would cause odd resonance or make it sound funny like that. figured worst case I may sacrifice a small amount of bottom end.