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Thanks to Gazcw on the "other" Maserati forum - here is thread with a video showing there are indeed spring-loaded internal valves in the QP Mufflers.
 

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What? internal valves!?! That would explain a tone change around 4000 rpm. But others have opened up QP5 mufflers before to modify them and have not seen internal valves... must be a later QP5 "S" thing? So why didn't Maserati ever promote these or even have any info at all that they even exist? They must have different part numbers... Maybe not all markets got them? Now someone needs to open theirs up and figure out the simplest and less intrusive way to keep these valves open.
 

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So I just went and started my 11 QP S and exhaust comes out of both pipes equally. Doesn't seem like there is a valve in it. So here is a theory... maybe this was a 2013 QP5 thing only. According to some documents and the 2013 manual the 2013 has more HP than the 11's or 12's maybe as a result of this one year only muffler?

12 cylinders when you start your 2013 does exhaust come out both tubes? Can you ask Gazcw what year his is?
 

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I started up my QP and exhaust comes out of both exhaust tips. So that would suggest that I do not have the spring loaded flapper valves. Sheesh....as if there isn't enough confusion regarding these Maserati exhaust systems!!!
 

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Looking at other pics of cut-open mufflers, it looks like exhaust will always exit both muffler tips. Maybe the flapper valve simply allows more exhaust gas to move through the free-flowing passages...
 

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Gazcw here. Mine is a 4.7 S 2008. It is very possible the pressure is equal although I never checked that. As the exhaust gases enter the box, the flap is pushed and opens the valve slightly in the large bore pipe. The rest of the gases flow through the baffle and out of the narrower pipe. As the pressure on the flap increase, the valve opens and gases take the shortest route out so you should get more pressure from the larger tail pipe.
If you take the box off and get a camera passed the s bends, you should see theflap at the end. If it is open I guess you have no valve.
 

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What? internal valves!?! That would explain a tone change around 4000 rpm. But others have opened up QP5 mufflers before to modify them and have not seen internal valves... must be a later QP5 "S" thing? So why didn't Maserati ever promote these or even have any info at all that they even exist? They must have different part numbers... Maybe not all markets got them? Now someone needs to open theirs up and figure out the simplest and less intrusive way to keep these valves open.
I can try and get the part number off of mine this week. Also, you could contact Jarens Metalworks that did mine. He also posted some videos on you tube under that name. Remember I also have an unsilenced x pipe so the music is a combination of both.
 

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I'm intrigued. Mine is a 2013 and I've been wondering about the exhaust too and what other things may be different to have the different HP rating.
 

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The OG forum members are well aware of this. We've done everything from welding the valve open, removing the fiber, re-channeling the flow with new tubes, creating different chambers, to gutting it completely.
 

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The OG forum members are well aware of this. We've done everything from welding the valve open, removing the fiber, re-channeling the flow with new tubes, creating
Wow I was under the impression that people who gutted their mufflers did not find valves inside, but I took another look at your "I cracked the sound code" thread and in a pic there that valve is with the parts that you cut out and removed.

So a couple questions...
Why does exhaust come out both pipes at idle? Also any idea what the simplest way to lock that valve open without opening up the whole muffler? Like a quarter sized opening in the right spot for access maybe?
 

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Wow I was under the impression that people who gutted their mufflers did not find valves inside, but I took another look at your "I cracked the sound code" thread and in a pic there that valve is with the parts that you cut out and removed.

So a couple questions...
Why does exhaust come out both pipes at idle? Also any idea what the simplest way to lock that valve open without opening up the whole muffler? Like a quarter sized opening in the right spot for access maybe?
The valve doesn't completely block off the secondary pipe, if I remember correctly.

The easiest way to access the valve is to cut it open. It's actually an easy job and if you cut it from the top, you can't see the scars with the mufflers mounted.
 
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