Please help me with my exhaust!!!!

[throttle out]

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
https://www.youtube.com/watch?v=Zy_jXZgFxJI&feature=youtu.be

 

[yevgenievich]

That might be just because of long tube headers. My 98 ls1 with long tubes sounds similar.

 

[Jarhead79]

I'd check all your gaskets ad make sure your bolts are all tight. It sounds to me you have a bit if a leak
or possibly you're hearing valve train tapping through the exhaust?

 

[throttle out]

I'm leaning toward a leak myself honestly, and have been looking at other flange options. If it is the long tubes causing the noise is there no way to reduce that sound? I did a good bit of research before deciding on the setup I went with and none of them have that sound that mine does.

 

[da_raabi]

Is that not the way true duals sound? An H or X pipe would probably clear it up. I've been meaning to do the same thing with mine. I have a similar sound - but no discernible leaks. I hate it. One of these days I'll try a Flowmaster bolt-on H-pipe and see what happens.

 

[yevgenievich]

It seem to be more pronounces with long tubes and true duals. Every true dual long tube car I had was similar. Might be that some had leaks, but that tends to be little different sound.

 

[Camar068]

what about a resonator? Was reading up on exhaust last night and came across them.

 

[crazy4offroad]

Probably the nature of the round tube mufflers. You can hear it in this one too...
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[yevgenievich]

An x pipe with resonators should help to clean up the sound

 

[throttle out]

An x pipe with resonators should help to clean up the sound

I'm leaning this way myself. There is a fella on ls1tech that insists one or both of my mufflers are installed backwards. Magnaflow clearly states that they are universal and can be installed in either direction, though he does have me thinking lol. I did notice last night that my shift linkage could be rattling up against the header on the driver side and on the passenger side it looks like the header is up tight against a boss on the block by the starter. I'm surprised I missed this, gonna have to pull the header to cut that boss off. Must have been excited to have the ole girl back on the road!!!

 

[glockholiday]

Wrapping the headers will change the sound.

And I didn't think you could here an exhaust leak after the mufflers but you can. Maybe weld instead of using those clamps. And run the pipes all the way over the axles.

And yes an H or X pipe will change the sound too.

In my opinion and some flow charts I've seen dual 3" is a little big for a small block unless you're making some serious power so a lack of proper exhaust scavenging sounds worse in my opinion also.

I'm running a single 3" on my TBI 350 and it sounds a little big to me.

 

[throttle out]

Wrapping the headers will change the sound.

And I didn't think you could here an exhaust leak after the mufflers but you can. Maybe weld instead of using those clamps. And run the pipes all the way over the axles.

And yes an H or X pipe will change the sound too.

In my opinion and some flow charts I've seen dual 3" is a little big for a small block unless you're making some serious power so a lack of proper exhaust scavenging sounds worse in my opinion also.

I'm running a single 3" on my TBI 350 and it sounds a little big to me.

I've been waiting to get my receiver hitch mounted up before I finish running the exhaust all the way out. Never occurred to me there would be a leak there being the very last bit of the system. I may pull them off to see what that does for the sound. I'm sure the drone will grow, but the sound I'm trying to be rid of may certainly change.
Thanks for your input!

 

[MikeB]

I'm gonna say if it's leak, it would be more pronounced under load -- trans in Drive, foot on brake, and engine revved up against torque converter. And you'd hear it from one or both sides of the truck, probably even in the cab.

With a manual trans, it would be most noticeable when flooring the throttle in a taller gear from very low RPM, such as starting off in 2nd or slowing way down in 3rd and then flooring the throttle.

If you do have a leak, it will eventually leave dark exhaust marks near the header gasket surface, muffler clamp, etc. And it would show signs of condensation (water drops) if it's past the headers.

 

[MikeB]

In my opinion and some flow charts I've seen dual 3" is a little big for a small block unless you're making some serious power so a lack of proper exhaust scavenging sounds worse in my opinion also.

From what I've read, primary tube diameter and length are the most critical dimensions, and scavenging is pretty much finished past the header collectors. Now if the collectors are too short for the engine size and RPM range, some additional collector pipe length might help scavenging, but after that I think you want the least amount of flow restriction possible. In fact I once read an article by David Vizard saying that if it's not practical to use larger exhaust pipes to increase flow, try to use a larger muffler with adapters, for example 3" muffler with 2.5" pipes.

 

[Jarhead79]

From what I've read, primary tube diameter and length are the most critical dimensions, and scavenging is pretty much finished past the header collectors. Now if the collectors are too short for the engine size and RPM range, some additional collector pipe length might help scavenging, but after that I think you want the least amount of flow restriction possible. In fact I once read an article by David Vizard saying that if it's not practical to use larger exhaust pipes to increase flow, try to use a larger muffler with adapters, for example 3" muffler with 2.5" pipes.

This is what I've done on the last three vehicles I've had and have really been happy with how they ran, my challenger really woke up when I changed to dual 3" mufflers and 2.5 exhaust.
https://youtu.be/JC-0vOzi7rs