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Discussion Starter · #1 ·
Here is what I've come up with so far for a modified exhaust system. There are 2 mufflers on the Trailblazer. The first one which is right behind the catalytic is more of a resonator while the second one under the rear bumper is the main muffler. I decided to remove the rear muffler and put a y-pipe in it's place with 2 exhaust pipes leading up to the dual exhaust tips. I figured the huge rear muffler was very restrictive and just removing it results in very good power gains of at least 10hp and 10ft lbs tq. I honestly believe the gains are much higher, but I'm trying to be realistic at the same time.

Front muffler/resonator


Rear muffler


Here is where I made the cut to remove the rear muffler. I chose this location so that the muffler could easily be reinstalled with a butt joint band clamp and it worked good for the y-pipe placement.




Here is the y-pipe and dual exhaust pipes.




Custom adjustable hangers using narrow band SS exhaust clamps, SS threaded hex nuts and SS 10 x 1.5 x 130mm bolts. The bolts have the heads cut off and bent using a torch.


Exhaust pipes leading into the faux exhaust tips on the RS just like stock.


Some of the parts used. 2" SS 90° bends, 2" SS inlet/outlet y-pipe, 2" SS narrow band clamps, 2" SS butt joint band clamps.


I've now logged about 100 miles with this setup and the results are good in many ways, but more tuning is needed to refine the sound. For now everything is clamped to make adjusting and further modifications easy.

Pros so far-
Incredible power increase which is obvious right away.
Being able to hear what the engine is actually doing.
Losing over 20 lbs off the rear end.
The deep exhaust sound the little 3cyl makes.

Cons so far-
A little louder than I want it.
Some exhaust drone and resonance while under a load.

I'm looking into adding 2 small resonators or bullet mufflers (1 on each exhaust pipe after the y-pipe). I believe most of the resonance is due to the long run of exhaust pipe after the first muffler/resonator. This is why you often see resonators/mufflers near the end of the exhaust on most vehicles. Since we have a resonator up front I'm guessing the 3cyl makes some unwanted noise/resonance immediately after the cat. Adding some resonators to the rear should also cut down on the intermittent drone too.

I'll get an exhaust clip soon, just waiting for my camera to charge which hasn't been used in years, lol. My camera records sound better than my phone, so I'd rather use it for a more accurate sound clip.
 

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Looking forward to the sound clips.
 

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Discussion Starter · #5 ·
Looking good but your not gaining any power. Despite the perceived feeling you'll never gain more only open the powerband up for what's available.
Agree to disagree. The power increase is very noticeable and not my imagination. The increased hp/tq is by far the most I've experienced on any vehicle I've done custom exhaust intake work on without also tuning the PCM. If I could tune it to match the increased airflow going in and out I'm sure there's alot more left on the table. I do agree that it shifted the poweband lower which is why the acceleration improved so much, but having done this type of work for 30 years now I can say my 10hp/10tq guess seems low. That rear muffler is extremely restrictive and makes way to much back pressure which turbo engines don't need. The turbo and cat are more than enough back pressure.

I'm going to do some data logging with the factory muffler and with the y-pipe setup. I really want to compare air/fuel ratios, short & long term fuel trims, ignition advance, 02 sensor ranges and about 20 other parameters to see how each setup behaves and to make sure the stock tune isn't running too rich or lean.
 
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Discussion Starter · #6 ·
2021 Trailblazer RS, rear muffler deleted, y-pipe added.

Not the best sound clip, but it's the best I can get right now with my old camera. It sounds better with headphones on, but even then it still doesn't sound accurate. It has a much deeper sound in person, not like a lawnmower, lol. Time for a Go Pro. Once I swap in some resonators I'll try again.
 
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Agree to disagree. The power increase is very noticeable and not my imagination. The increased hp/tq is by far the most I've experienced on any vehicle I've done custom exhaust intake work on without also tuning the PCM. If I could tune it to match the increased airflow going in and out I'm sure there's alot more left on the table. I do agree that it shifted the poweband lower which is why the acceleration improved so much, but having done this type of work for 30 years now I can say my 10hp/10tq guess seems low. That rear muffler is extremely restrictive and makes way to much back pressure which turbo engines don't need. The turbo and cat are more than enough back pressure.

I'm going to do some data logging with the factory muffler and with the y-pipe setup. I really want to compare air/fuel ratios, short & long term fuel trims, ignition advance, 02 sensor ranges and about 20 other parameters to see how each setup behaves and to make sure the stock tune isn't running too rich or lean.
I get what your saying and feeling but your not adding anything to the crank numbers without a tune. You are likely adding to the wheel numbers no doubt with the added air and exhaust flow. 10 to 15hp max and that's with the K&N filter. You know that I know that but others see it adds 10 to 15 and they are like kids in a candy shop. Not a bad thing but they can get disappointed and butthurt real easy.
 

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Great job!! But now after hearing this I really wonder if taking out the forward silencer might sound better.?? Your thoughts?
 

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Discussion Starter · #12 ·
Great job!! But now after hearing this I really wonder if taking out the forward silencer might sound better.?? Your thoughts?
Was wondering the same thing, but I still think it would still need some resonators near the end of the exhaust to get rid of the drone/resonance. Another idea I had was 3 bullet mufflers which are essentially the same as resonators, 1 to replace the front muffler and 2 more after the y-pipe. One thing I have learned so far is the rear muffler is very restrictive. I know GM was more concerned with sound control than losing some power, but this was a bit too much. I also see a real market for a well made high flow exhaust now. I wasn't sure before, but it's clear there are good gains to be had by uncorking this little engine.
 
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Was wondering the same thing, but I still think it would still need some resonators near the end of the exhaust to get rid of the drone/resonance. Another idea I had was 3 bullet mufflers which are essentially the same as resonators, 1 to replace the front muffler and 2 more after the y-pipe. One thing I have learned so far is the rear muffler is very restrictive. I know GM was more concerned with sound control than losing some power, but this was a bit too much. I also see a real market for a well made high flow exhaust now. I wasn't sure before, but it's clear there are good gains to be had by uncorking this little engine.
Take a look at that Vibrant Performance muffler for the rear. Would allow you to have the single input and dual output. Vibrant is the only company that I found that has the side input and dual output. And Vibrant sounds really nice



 

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Discussion Starter · #14 ·
That might work. My concern would be the large inlet and outlets. Our entire exhaust is 2". This is one area where going bigger is not always better unless the whole exhaust is also bigger, but with this little engine I do believe 2" is adequate. 2.25" might offer some improvement, but anything bigger is actually going to slow down exhaust gasses which can result is less power. I know it sounds weird, but exhaust gasses flow faster over a hot surface and keeping the exhaust pipe the same size from the manifold to the exhaust tip keeps the gasses hot so they flow faster. Some manufacturers actually reduce exhaust size for the tailpipe/s in order to keep exhaust velocity high. Someone could probably explain this better than me, but it is one of those laws in thermodynamics. Even my setup is not ideal since my main 2" exhaust goes into a y-pipe and then has two 2" exhaust pipes exiting. A better balanced set up would be 2" in and two 1.5" pipes existing.

Does Vibrant make they same muffler with a smaller inlet?
 

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Discussion Starter · #15 ·
I get what your saying and feeling but your not adding anything to the crank numbers without a tune. You are likely adding to the wheel numbers no doubt with the added air and exhaust flow. 10 to 15hp max and that's with the K&N filter. You know that I know that but others see it adds 10 to 15 and they are like kids in a candy shop. Not a bad thing but they can get disappointed and butthurt real easy.
I think we are just looking at this differently. For example the engine in a C8 is rated at 495hp/470tq, but adding a new exhaust system can add as much as 30hp without any tune. Does the engine make more power? I'd have to say no like what your saying. Did it free up hp that was already there by removing restrictions. I'd have to say yes of course because it wouldn't dyno at 425hp if something didn't improve. I've seen many dyno tests of engines on stands and engines already in vehicles. Engines by themselves don't gain hp/ tq without a tune, but when we're talking about production vehicles there are all kinds of restrictions in the intake and exhaust that when opened up do increase the hp/tq numbers. The power was already there, it was just restricted or "reduced" due to the manufacturer adding sound control in the form of baffles, anti resonance chambers, etc in the intake and exhaust. Removing these restrictions just makes the engine breathe easier which adds back hp/tq that was robbed when they tried to make everything quiet.
 
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Discussion Starter · #17 · (Edited)
Inlet and outlets are good. Placement might be a challenge though.

Here is the top view of the factory rear muffler for reference.


You can look at transverse mufflers for some good ideas. Muffler design is also important on a turbo engine. A straight through style like a bullet muffler similar to an old school glasspack is better than a chambered muffler. The reason for this is because of the backpressure the turbo makes so you want high flow after the turbo/cat. On a non turbo engine a chambered muffler like a Flowmaster works better because it adds some backpressure and scavenging which increases efficiency.
 
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Could you place it where you have the Y pipe?
 

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And unfortunately Vibrant does not make that muffler in a 2". I wish they did
 

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Discussion Starter · #20 ·
Could you place it where you have the Y pipe?
Yes, but you would definitely lose ground clearance. With the y-pipe I lost about 1" which isn't too bad, but a muffler in the same place would definitely hang lower.





 
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