Z.06

I had the Muffler Mod performed by Roger Witham of Texas Quality Performance Exhaust about 4 years ago. Roger uses the welded sleeve technique, not the bolted technique. I really enjoyed the exhaust note until about 6 months ago when an annoying resonance showed up at about 2500 RPM. Annoying is not descriptive enough. The noise made my car sound like the cheapest POS on the street. When I went looking for Roger, I could not find or contact him. The website was down, so I had to find a different solution.

After a while I could not take it anymore so I borrowed a lift and removed both mufflers and carried them across town to be cut open. I was suspecting cracking of the internal baffles. After all the effort to open both mufflers, we were not able to find any cracks. None. The advice give to me was to look for rubbing between the exhaust and the frame. On reassembly, no rubbing could be found and I had 1/4 inch of clearance everywhere. The resonance was still there. I retorqued all of the fasteners with no improvement, then I implemented the hose clamp fix on the muffler rubber hangers. Still no improvement.

I took the car to a well-regarded muffler shop and they could not find any problem from external inspection. Then I took my Z06 to Corvette World (used to be Corvettes of Houston). They drove and diagnosed the car and found the noise was coming from the driver's side muffler.

About this time I found that Roger was still in business and was in exactly the same location as before, about 55 miles away from my house. I went to Roger's and he said he knows how to fix my car based on things that he has learned since my original conversion. He removed the driver's side muffler and opened the side to expose the internal pipes and baffles, which appeared perfect. WTF? On closer inspection he found one small crack in a baffle, where it was penetrated by the perforated pipe. When Roger welded the crack up, he had to chase it a bit as the heat from the weld process caused the crack to run. Then he layed down more weld where the pipes penetrate the baffles, then he welded angle iron braces to both internal baffles. Roger reinstalled the nasty glass fiber stuffing at my request, and welded the rectangular shell piece back in place to seal the shell.


Then Roger tried to remove the passenger side muffler and found that it did not want to be removed, so he opened up the shell with the muffler/pipe hanging from the car. On inspection, no cracks could be found. Roger layed weld material at the junction between the pipes and the internal baffles and welded in angle iron braces just as on the other muffler anyway. Then he reinstalled the glass fiber stuffing and welded the muffler shut.

The result was perfect, and fingers crossed it will stay that way forever.








Weld bead tracing upper crack as well as angle iron brace between crossover tube and straight through tube and baffle wall beneath.




Passenger side muffler had no cracks, but the tube to baffle welds and angle braces were installed anyway.

jasonz28camaro

I could have helped if you posted prior to searching for Roger. I live near you and could have got you sorted out.

Not sure what he used to originally weld the sleeve but looks like he used short circuit mig for everything else, very common in the muffler industry. When I do them I use a very small diameter rod and stick weld the sleeve over the pref pipe then tig weld the shell shut (only because I do not have a mig welder anymore). Looks like he spent a good amount of time welding the shell back on with all the starts and stops but got it done either way.

For anyone else trying to do this Id recommend either stick welding the tube or use flux core simply for the penetration so it does not fail ever. Also, no mater how clean you try to make it the tubing you are welding is inside a muffler and will have soot and these two processes respond well to dirty surfaces. Dont stick weld the shell unless you know what you are doing.

rio95

Dang that's a lot of screwing around. Kind of glad I went aftermarket. Glad u figured it out.

Pb82 Ronin

Any reason you didn't buy new mufflers? They aren't that expensive. Sounds like it would've saved you a lot of headache.

Z.06

Jason - The bead that you see on the shells of the mufflers results from two weld closures. Now the mufflers have 3 weld closures and flat black paint is over the welds. The welds are on the sides of the mufflers that faces each other and the mufflers are only about 2 inches apart, so no one can see the welds unless they are really looking for them.

rio - regarding too much screwing around, the blame for this belongs to both me and the guy who cut them apart a couple of months ago. He is on the forum and will probably see this, but I will not name him. I had my chance to look inside the mufflers at the time, and I did not see the crack either, but we had every opportunity to find it then. Immediately after reassembly, the very same resonance was evident. Lesson learned is to look very, very carefully and feel the areas around where the tubes intersect the inner baffles.
I was not interested in going aftermarket as many of those systems have serious drone issues and they all have a large Corvette tax applied to the price.

Smokin - I have to disagree with you on the cost of aftermarket. To get what I wanted would have cost me $2000 installed. Fixing what I had was 1/4 that. Keep in mind, replacing one side with the OEM exhaust system would have been $1400 for the part plus over $300 labor, and what I would have had for that expenditure was a half-modded muffler system.

Pb82 Ronin

$2k??? Really? Find a new shop bro. Here's a list of Borla mufflers: https://www.borla.com/products/specialty.html
All of which are under $300. So, roughly 600 if you had them shipped. To cut out old mufflers and install new ones should be nowhere near $1400 in labor. If it was...like I said, a new shop is needed. Just trying to help...either way, glad you got it fixed.

ToppThat

I modded mine welding the pipe over the perforated pipe 3 or 4 years ago never had any problems ( except hearing loss but out of boredom I'm getting the gen 3 fusions they'll be getting sold soon

Z.06

Ronin,
You are talking about replacing mufflers and I am talking about replacing a bi-modal exhaust system. The only aftermarket replacement I even considered is the B&B Fusion Gen 3, which is a bi-modal exhaust system. The B&B parts normally cost about $2150, but I have seen it on sale for about $1650 if memory serves well.

The likelihood is that simply installing a catalog Borla muffler would result in exhaust drone, as it would not have a bi-modal system to control the exhaust back pressure. The Borla mufflers would have to be adapted such that the exhaust tips would match the Z06 specific exhaust locations and the support points for the Borla would have to be added to match the support points in the Z06 chassis.

I would not have accepted the exhaust drone, and deletion of the bi-modal system would have probably reduced the resale value of my car, if I ever want to sell it.

Topp - What this experience has taught me is that even though the modded muffler is fine for 3 years or for 4 years, it does not mean that the result is guaranteed forever. I can tell you definitively that my modded exhaust system was completely perfect ... until it wasn't. So take whatever comfort in that you can.

Pb82 Ronin

It's your car and your money. Plus, you've already made the decision. So the point that I was making is moot anyway. All I'm saying is...

A muffler can go anywhere in the exhaust system and work just fine. While I can understand wanting it in the factory location for style and appearance...installing the flapper and a hangars on a dual outlet muffler (including in the factory location) is NOT a difficult job. The "bi-modal" you mention is nothing more than an electronic flapper that opens on one of the two outlets at WOT. It's easily removed and reinstalled with a pipe cutter and some welding.

Either way...glad you're up an running trouble free again.

Z.06

Ronin, I recommend you Google bimodal exhaust systems, or even search them in CF. You will see some diagrams to explain how they work.

Thanks. I am glad to be up and running again as well. I hope you will do a little research into how a bi-modal exhaust works and think about my comments. My only goal is to help people understand that the OEM Z06 exhaust system is not a pair of dual outlet mufflers.

If you still believe I am wrong, you should ask yourself how B&B is making a business selling bi-modal exhaust systems to Corvette Z06 owners at $2150 a pop. My BMW 335i sedan OEM exhaust is a bi-modal design as well.

For those of you who believe that they have no problems with a loud exhaust and exhaust drone at freeway speeds will not be a bother, all I can say is try it and see if you like it. Most people find exhaust drone unacceptable, and this has been my experience as well. If you are well and truly deaf and take no passengers, you can always turn off your hearing aid.

jasonz28camaro

OP is correct. Muffler mod is the best bang for the buck! In my opinion the Fusion exhaust is the only alternative but it is 2k. So if you have 2k you want to spend on exhaust then go Fusion or whatever your friend says is the best mufflers, if not do the muffler mod. I personally have done it a few times and charge $100 to do it. I weld as a hobby, I do not work at a shop.

There are probably dyno results somewhere comparing the two. Someone recently modded the mufflers so far that they matched the Fusion almost exactly and it gained all of 5rwhp. I would not pay $1900 for 5rwhp.

For the member saying you can spend a couple hundred cutting and welding new mufflers in you know you are talking to Corvette owners right? Nobody wants to hack up their exhaust like an f-body. The mod is one thing but when you start cutting on this stuff is where you start to not care. I've done my fare share of hackin and welding and trust me if they made a bolt on id jump at it.

Bi mode rocks too. Kill the drone instantly when you get a headache.

Pb82 Ronin

You can church it up however you want man. It's nothing more than a single inlet dual outlet muffler (only difference being one of the internal "tubes" is straight and "bypasses" the muffler chambers) with that outlet being blocked by an actuator valve. It's regulated by a vacuum signal and electronically actuated. I know how it works. Always have. I also know that almost ANY performance muffler can work exactly the same way when you install the "flapper", valve, actuator, vacuum assisted electronic solenoid...(or whatever other title you want to call it to make yourself feel smarter) onto one of the outlets. The ONLY difference is that it wouldn't be passing through a section of straight (unperforated) pipe. But since most aftermarket mufflers are perforated straight pipes with sound isolation matting (IE Borla, SLP, etc) which is the same as the "bimodal" side anyway... the aftermarket muffler would have been lighter, sound better, make more power, and was probably just as inexpensive...or even cheaper than the route you took. Any GOOD muffler shop or shop with a good welder could have done this for you.

If "drone" is really the problem, then you made the right decision since the factory stuff is so tame and quiet...even when the flap is full open (which is how I have mine all the time). Even then, it's sounds like a Cadillac to me.

Either way...I could care less because as I said, you already made your decision. I was only saying that there are potentially better routes to take rather than turning an OKAY system into an ugly OKAY system and gaining nothing from it except a lighter wallet.

Pb82 Ronin

Umm...I did say take it to a GOOD shop. Take it to MIDAS, and you'll get what you pay for. The shops corvette guys USUALLY go to make the factory welds look terrible.

And the reason B&B can charge so much? Because corvette guys are willing to pay the "Corvette tax." That system probably costs them about 400-500 bucks to manufacture.