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Discussion Starter #1 (Edited)
I came across a resonator mod they've been doing on Corvettes for the past 10 years. Drilling into brand new C6 and C7 vettes. I recently reviewed some glasspacks I put on and after doing this, putting those mufflers on was a waste of money.

No rasp, no drone, deep rumbling sound, even at idle on my 2016 A8 RT Shaker, in a half hour, and almost for free. This is magic. I'll post links to the Corvette thread and to a Corvette vid below. The pictures are mine. The Corvette resonators are somewhat the same as those on the RT's with a front and rear chamber.

It is so simple. You just drill a hole into the rear chamber of the resonator at a 45% angle and then through both sides of the tail pipe as it passes through the rear chamber, then you cap the hole you initially drilled through the outside case of the resonator. What this does is allow a percentage of direct sound in the rear chamber to go straight out your tail pipe.

The Corvette guys found that a 3/4" hole was where they started to see the slightest bit of drone. I myself have stopped at a 1/2" hole because it already sounds good but I have the plugs for a 5/8's hole if I decide to go further later on. The plugs can be bought at any auto parts store. They are called button plugs. You want the nickel plated ones, not plastic (duh). Cost $2 for a pair. I sealed them on with some RTV sealant. I had grey in my garage which is good for 625 degrees and is muffler grey, lol

Just a note that I jacked the back of the car up a few inches to do this and drilled a smaller hole before the 1/2" bit. I eyeballed the angle by looking down the tailpipe. Like I said, I'll probably move up to a 5/8's hole now that I know a 1/2" works good. I intially went with 3/8's holes and plugs before moving up to 1/2.

This is a before/after vid from a Corvette. This takes our RT from zero idle sound all the way to close to this. (You need good speakers to get a full understanding what it does.)

Finally, here is a Corvette thread on this that has been running for 10 years. When they started, it was kind of archaic but they have refined it to what I just showed you. It is hours of reading so I suggest you start on page 15-20 if it interests you because that is the point where they figure out to use the button plugs
Stock muffler mod... - Corvette Forum
 

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Nice briefing, interesting idea.
 

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Discussion Starter #3
It works better than you can ever imagine. Even if you have nothing in your garage, buying everything costs $20. I said the word magic because I meant it
 

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hmmmm
 

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Discussion Starter #5 (Edited)
How big and what sound you can get hasn't even been reached yet. Obviously, you want to end up with the outer casing capped off so it all goes out your tailpipes but you don't have to experiment like that. What I saw in the vette forums is that they ran and experimented with all holes open until they reached a size that created drone. Then they capped off the outer casing, thereby closing off one of three holes in the resonator. Drone went away and it got a little bit quieter.

Because I'm the guinea pig over here in Dodgeland, I started with 3/8s open. That gave me really good sound and no drone. I then capped The 3/8s and it got quiet so I pulled the plugs and went up to 1/2" capped. That sound is good but still quieter than the 3/8s open so I know I can go to at least 5/8s capped without a problem. Maybe more.

One other thing. I saw in the vette thread, the guys mentioned it didn't seem to bother their wives that they did this. I'll tell you my wife *****ed for 5 years about my last Camaro...."why did you change the mufflers, it was such a nice quiet car, why, why why, blah, blah blah". After I went to 3/8's open, which has been the loudest so far, I took my wife out. My wife does not know that I have changed the exhaust on this car in any way, including the glasspacks. I learned that lesson the hard way. Anyway, I was prepared with an explaination if needed...."you know dear, these big V8 cars get a little bit louder after they break in after the metal in the exhaust expands and contracts for a bit of time". So we go out annnddd: nothing. Didn't notice a thing. Meanwhile, we sit at lights with the car idling with sound, dum dum dum dum
 

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I'm not bashing this concept at all and its a good write up, but in now way will a small hole through the end pipe within the existing reso chamber substitute or equal the sound and lack of downstream flow restriction produced by the actual removal of the entire resonator from the end of a 2.25 / 2.5" exhaust system.
There is another benefit to the reso-delete mod that this doesn't do and that's losing the plus 50 lbs of weight the two of them add to an already heavy car. Anyway, hope it works for you.
Hemi4us
 
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Discussion Starter #8 (Edited)
Well, if you have an automatic, there are at least 50 posts in these threads warning you not to remove your resonators, and people wishing they hadn't done that, because it's drone city. So option 2 is remove and straight pipe the mufflers. Some people like it, some don't because it's raspy. Option 3 around the rasp is change out the mufflers for something smaller. That option included me. What you get is a bit better sound but still quiet. What this mod does is gives the automatic owner a percentage of the direct sound before that percentage tips the scale into the drone zone. And you pay for it in pocket change.

Also, and maybe I'm wrong here, but I'm pretty sure x pipes like we have on the Challenger are there to counteract flow restriction. Pretty sure they first showed up on Corvettes years back also. And if they're putting similar resonators on Corvettes, I think it's safe to assume for one reason or another, the flow restriction is minimal.
X pipes explained:
http://www.superchevy.com/how-to/exhaust/1504-x-and-h-pipes-add-easy-horsepower-but-which-is-best-for-your-ride/
 

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Okay, so who is gonna test this out on their own for results? Also drex, did you say that you have glasspacks on your Challenger? So you replaced the mufflers with glasspacks THEN did this mod? You were able to hear the difference still?
 

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I may try this when I get home today, seems interesting. I planned on replacing my resos anyways, so if it doesn't come out good I'll just cut 'em.
 

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Discussion Starter #13 (Edited)
Okay, so who is gonna test this out on their own for results? Also drex, did you say that you have glasspacks on your Challenger? So you replaced the mufflers with glasspacks THEN did this mod? You were able to hear the difference still?
Absolutely. This changed the sound of the car as much or more than the glasspacks did and I'm only running 1/2" holes yet. How big can we go? Pretty sure 5/8's is no problem. 3/4's like the Vettes? The surface area of 5/8's is 50% larger than the surface area of 1/2". And the surface area of 3/4's is 50% larger than 5/8's.

So, if we can go as large as 3/4", I can tell you a 3/4" hole is more than double the surface area a 1/2" hole. So my 1/2" hole might not even be attaining half the sound available.

Just a note to Tynarus or whoever wants to try this for themselves. If you plan on starting out or going bigger than a 1/2", a hole saw might be an option for you
 

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Hope someone can try this on all factory stock system....and maybe before and after vid....
 

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My poor little cordless drill couldn't take it, and died before I even got through the wall of the first resonator haha. To be fair though, I didn't exactly charge it before-hand...

Oh well, I'll let her charge and give it a shot tomorrow. :)
 

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Discussion Starter #16 (Edited)
Just in from opening it up to 5/8's. I had looked for a 5/8's bit here this weekend and didn't think I had one but another trip out to the shop tonight and I found one tucked away. The 5/8's bit is a weapon. It took 45 minutes instead of 30 and the extra 15 was me lying on my garage floor panting from time to time. Seriously, at this size, I think hole saw is the way.

I was fine at 1/2 hole but this is what I'm chasing: the vette guys rave about the burble they get on decel with this. I've had that burble before on another car and that is some sweet ass music. At a 1/2" in sport mode where the transmission is tight, it is almost there, right on the cusp, trying to happen. Hopefully this puts me over the top. If you don't know what burble is, go play that vette video I posted in my first post with some speakers better than what comes with a laptop. Right at the end of the video, after he whines it out after the mod, it burbles a bit after he lets off the throttle

So, RTV is setting and I'll report back in tomorrow with my final results.
 

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I have my muffler deleted and only have the resonator. I'm glad there is some discussion around how long it is taking with some of these drills... I have a step bit that might do a better job of working up to the right size, but I dunno if I can get it in there to hit the pipe on the inside.

Won't a holesaw be a giant PITA to get it to "bite" at an angle like that? I've only had luck with those when they are flat against the material. You could probably cut the first one that way, but after that it may be hard to get the insides done with a hole saw. I have no evidence here, was just thinking about it.



So hey drex, sound any better today?
 

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Also, and maybe I'm wrong here, but I'm pretty sure x pipes like we have on the Challenger are there to counteract flow restriction. Pretty sure they first showed up on Corvettes years back also.
I can't tell you exactly when the "X" pipe first showed up, but its just an evolution of the "H" pipe that 440 and Hemi Dodge/Plymouth B-bodies had in the late 60s. I think the big Chryslers (like the 300 and Imperial) probably had it in the 1950s. Its there to counteract the tendency of one cylinder on each bank of a V8 with a "90-degree" crankshaft to see higher backpressure than the other three. That happens because a 90-degree crank V8 doesn't strictly alternate banks left-right-left-right-left right the way a 180-degree crank V8 (Ferrari v8, the current Mustang GT350 v8) does. That would be just like two 4-cylinder engine exhausts, and the flow is nice and even in both the left and right exhaust systems, even if they don't connect with each other. But a 90-degree crank v8 fires L-R-L-L-R-L-R-R-L-R-L-L. If you don't connect the two tailpipes, those pulses of higher pressure have to work their way all the way through the system. But letting the two tailpipes connect together before the mufflers balances the pressure on those "double" pulses, venting some of it off to the other bank's muffler. An "H" pipe does it OK, but the "X" pipe does it so the gasses don't have to turn sharp corners. In all honesty, a length of SINGLE pipe of very large diameter is just as good, but people don't like that because its not "true dual" exhaust. The firing pattern is also is what makes 90-degree cranks sound so much "deeper" and rumblier than flat-plane (180 degree) crank v8s... which literally do sound like two 4-bangers running at the same time.
 

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I may have messed up and went a little too far forward. We'll see shortly.
 

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Hm. Doesn't appear to alter the sound any if you hit the wrong chamber. Sounds like stock. So all good, I guess.
 
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