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Cutting the Baffles from a Stock Muffler
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mark tucker
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PostPosted: Tue Jan 24, 2012 12:42 pm    Post subject: Reply with quote

2" 3 chambered turbo is kinda loud, but if you make a plug for the chamber the inlet is inline with it gets real quite fast, and still flows plenty for our little cars.
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PEPPE
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PostPosted: Tue Jan 24, 2012 3:57 pm    Post subject: e Reply with quote

i' ve made many of them, especially for bigger than stock engines.
the trick is to calculate the surface that "see" each port, measuring the diameter and number of holes and mantaining some restriction.
some mufflers are really restricted. some are unbelievably built with errors, that cause some cylinders to work different from another.
i believe for ease of construction or unknown reasons.
this summer i made also one for a T4 bus. it was like a banana in the exhaust...before...
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Gerrelt
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PostPosted: Sat Apr 18, 2020 8:20 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

Yep, old thread, but this thread helped me in modifying my stock muffler. So I wanted to return the favor.

I am modifying a stock muffler for my Alfa Romeo engined beetle.
For this I opened a Ernst NOS muffler, and because that is something not many people get to do, I filmed it.
Other people might find it handy if they decide to modify a stock muffler (or are just curious in what it looks like inside):


Link


These images can be found in the video, but they might be interesting on their own too:

Image may have been reduced in size. Click image to view fullscreen.

I found it funny that the sound comes from one peashooter, then both, then the other one, and then both again.

Image may have been reduced in size. Click image to view fullscreen.

A cone in a dome, pretty restrictive..

For my project, I removed the inner cones, and the tubing in the middle section (edit: because Alfa engine has exhaust outlet at the bottom, so shorter rear exhaust tubes). I also added holes to the dome, and the inner baffles.
I'll be using bigger pea-shooters too, with a bigger inner diameter.
It's not done yet, but I hope it will sound decent (=not too loud).
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Last edited by Gerrelt on Sat Apr 18, 2020 10:28 am; edited 1 time in total
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PEPPE
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PostPosted: Sat Apr 18, 2020 8:36 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

removing the inner tubing is wrong. it helps having a long primary tube for cylinders 2 and 4. this feature was in original vw mufflers and the leistriz. was also eliminated in later Ernst to spare money.

it was ok to make more holes near the end of those tubes and increasing also the number of them in the circular chamber separators.

good about the additional holes and cone removal in 1 and 3 baffles.

however you have to calculate the surface of the total holes to mantain a good proportion in the gas flow. otherwise you will make too much noise and loose low rpm torque.

unfortunately those mufflers are long gone. that should be early 80. 90s ERNST are much different than that
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PostPosted: Sat Apr 18, 2020 9:57 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

PEPPE wrote:
removing the inner tubing is wrong. it helps having a long primary tube for cylinders 2 and 4.


Yes, you are right, I forgot to mention that the Alfa Romeo engine has the exhaust outlets at the bottom, not at the sides like the Beetle engine. This makes the tube lenght difference between the front and back cylinder a lot smaller.
So, in my case, it's OK to cut the middle tubes out. But you shouldn't do it for a VW beetle engine.
You have to try to make the lenght exhaust gasses path from each cylinder to the muffler roughly the same.
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PostPosted: Sat Apr 18, 2020 10:17 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

yes sounds a good thing. i would use the center chamber for all 4 cylinders and use the side chambers as expansion before exiting.

if you dig around there was an italian kit car, PUMA boxer 90 that used 1500 engine from alfa sud and 33 with an homologated specific exhaust. you can search around for it. maybe you can replicate it and should be the perfect one for the application
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PostPosted: Sat Apr 18, 2020 1:09 pm    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

PEPPE wrote:
yes sounds a good thing. i would use the center chamber for all 4 cylinders and use the side chambers as expansion before exiting.

if you dig around there was an italian kit car, PUMA boxer 90 that used 1500 engine from alfa sud and 33 with an homologated specific exhaust. you can search around for it. maybe you can replicate it and should be the perfect one for the application


Yes...technically that is how Ernst and others do it o the type 4 engine mufflers. The center chamber is used for expansion/collector for all 4 cylinders to create a homologous exhaust pressure.....and then its collected into the outlet pipe in the end chambers ...and one sub chamber. Each one of these chambers is sized to be a specific resonator.

Eve though you guys are working on type 1 mufflers...this may interest you at least from a technical perspective. I dissected an Ernst type 4 muffler a few years back.

https://www.thesamba.com/vw/forum/viewtopic.php?t=653839&highlight

Ray
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Gerrelt
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PostPosted: Sun Apr 19, 2020 1:14 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

Thanks Ray! Yes, that was an interesting read.

One thing that is interesting in comparing the type 4 muffler to the type 1, is that the type 4 muffler uses stainless steel fiber in the "end stage", just before the exit into the tailpipe.
The type 1 muffler uses the two peashooters with stainless steel fiber (or something similar) in it.
Both server the same purpose probably, noise reduction, the other chaimbers are probably, as you said in the thread, resonators to reduce "hum" or "drone" at specific RPM's.
I hope the drone isn't too much with my "backyard" modifications..
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PostPosted: Sun Apr 19, 2020 5:45 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

Hello
This is basicly a reply to both the type4 thread and this one.

Wrt the cheap 4 into 1 Bugpack, T-bird etc header in the other thread. While I canīt say for sure how a D jet engine will respond to it, I can say that a stock carbed 2 l. engine reponds nicely. Over 25 years ago when we began racing our first mule was a T25 with a then stock 2 liter type 4. When hauling the trailer at elevated paces the oil and head termps were on the high side, OK at nights but critical in the daytime. So we replaced the stock muffler with one of those headers and made our own free flow header. This actually gave us just a little more pulling power up in the rpms. Iīm not sure if it resulted in a power drop down low. If it did it was not something we noticed. It ALSO resulted in a full 10 degree drop in oil temps when hauling the trailer. (Later that same engine got 28 mm venturies in the stock carbs + a rejet, which was quite a challenge to get right, but total it gave us 10 hp more over stock and a very noticeable 10% increase in torque in the driving rpm. The issue with the primaries not being same length doesnt mean squat on such an engine, in fact on engines with peak hp below appox 6000 it has very little effect. Yes 2 cylinders will pull max torque at a little different rpm than the 2 others, thatīs it. We can discuss the short stamped collector, but in general the header does a better job than it looks. On my now obsolete econo 2200 type 4 split bus set up I pulled 150 hp through that type of header.

It is kinda the same thing with the VS muffler, only the muffler is best for engines with peak power below approx 5300 rpm. The short headers provides for good lower rpm torque and the sound level in those are reasonable.

With the stock modified type 1 muffler. We do that every once in a blue moon when the owner wants more power, but absolutely stock appearance. a friend of mine, who is a skilled metal worker cuts them open, harvest the guts and makes 2 & 4 cross, sort of as in the above picture, but they exit out the ends, not through a perforated tube. Then the ends of the muffler recieve a "double layer" so that you have an inside temperature shield so to speak. Then over the outlets for the end pipes he makes a perforated screen which has the orifice square of 1 exhaust pipe + 5%. The end pipes are usually either TDE or CSP sport which has approx 30% larger orifice compared to stock. This way almost the entire muffler is a pressure chamber.
It works quite nice, is still reasonably quiet and is sufficient for about 80 hp. We did one for historic rally. On that one we did not install the screen over the end pipes. The historic engines pull about 125 hp, but they are loud.

If you want something with stockish look (type 1) and do not want the large can VS muffler there is also the CSP SS version: https://www.csp-shop.com/en/exhaust-heating/csp-high-flow-exhaust-251-001-030hf-30494a.html which is OK up to 85 - 90 hp max. Of course it does not support the torque improvement that a shorty header can provide, but it works well on engines in the 70-85 hp range. Done that a few times now, with nice and even power curves.

If you want something in black steel there is this one: https://www.hovwdiaudi.dk/product/?id=8120802400 It gives a deep throaty sound and performancewise very close to the CSP
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PostPosted: Sun Apr 19, 2020 7:49 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

Alstrup wrote:
Hello
This is basicly a reply to both the type4 thread and this one.

Wrt the cheap 4 into 1 Bugpack, T-bird etc header in the other thread. While I canīt say for sure how a D jet engine will respond to it, I can say that a stock carbed 2 l. engine reponds nicely. Over 25 years ago when we began racing our first mule was a T25 with a then stock 2 liter type 4. When hauling the trailer at elevated paces the oil and head termps were on the high side, OK at nights but critical in the daytime. So we replaced the stock muffler with one of those headers and made our own free flow header. This actually gave us just a little more pulling power up in the rpms. Iīm not sure if it resulted in a power drop down low. If it did it was not something we noticed. It ALSO resulted in a full 10 degree drop in oil temps when hauling the trailer. (Later that same engine got 28 mm venturies in the stock carbs + a rejet, which was quite a challenge to get right, but total it gave us 10 hp more over stock and a very noticeable 10% increase in torque in the driving rpm. The issue with the primaries not being same length doesnt mean squat on such an engine, in fact on engines with peak hp below appox 6000 it has very little effect. Yes 2 cylinders will pull max torque at a little different rpm than the 2 others, thatīs it. We can discuss the short stamped collector, but in general the header does a better job than it looks. On my now obsolete econo 2200 type 4 split bus set up I pulled 150 hp through that type of header.

It is kinda the same thing with the VS muffler, only the muffler is best for engines with peak power below approx 5300 rpm. The short headers provides for good lower rpm torque and the sound level in those are reasonable.

With the stock modified type 1 muffler. We do that every once in a blue moon when the owner wants more power, but absolutely stock appearance. a friend of mine, who is a skilled metal worker cuts them open, harvest the guts and makes 2 & 4 cross, sort of as in the above picture, but they exit out the ends, not through a perforated tube. Then the ends of the muffler recieve a "double layer" so that you have an inside temperature shield so to speak. Then over the outlets for the end pipes he makes a perforated screen which has the orifice square of 1 exhaust pipe + 5%. The end pipes are usually either TDE or CSP sport which has approx 30% larger orifice compared to stock. This way almost the entire muffler is a pressure chamber.
It works quite nice, is still reasonably quiet and is sufficient for about 80 hp. We did one for historic rally. On that one we did not install the screen over the end pipes. The historic engines pull about 125 hp, but they are loud.

If you want something with stockish look (type 1) and do not want the large can VS muffler there is also the CSP SS version: https://www.csp-shop.com/en/exhaust-heating/csp-high-flow-exhaust-251-001-030hf-30494a.html which is OK up to 85 - 90 hp max. Of course it does not support the torque improvement that a shorty header can provide, but it works well on engines in the 70-85 hp range. Done that a few times now, with nice and even power curves.

If you want something in black steel there is this one: https://www.hovwdiaudi.dk/product/?id=8120802400 It gives a deep throaty sound and performancewise very close to the CSP


Thank you for this answer!
With regard to type 4 engine response....your experience seems to be almost exact to what Jake Raby found with the T-bird type header (going off memory).

With regard to whether D-jet can feel the effect and benefit of a basic T-bird style header...yes it does. Very much so!.

Of course.....it has to be tuned for this fuel system wise. Its not a drop-in/swap-in replacement for the stock muffler. Many years ago I had one on a 412 I Acquired. It ran poorly on a low miles engine. It took me quite a while to tune the fuel system properly. From that point.....the T-bird style header and basic muffler created a major throttle response increase and noticable 55-70mph passing time decrease at highway speeds.

I did not know at the time it was really that much of an improvement....until it fell apart and I went back to a stock muffler. When the t-bird is installed on a,properly tuned D-jet system....going back to a stock muffler(I went back to a Leistritz/Walker unit) the difference in fuel settings is different enough that it caused a non-starting situation in anything but hot weather.

The issue I was hoping to clear up with this type of header unit with D-jet on a high compression type 4 engine.....with regard to equal lengths...and/or properly sized or shaped collector....is not an issue of small hp losses.....but mainly for smoother idle fuel tuning.
That was the only drawback of the T-bird with D-jet.

With carbs....a header and or cam combo that produces poor idle....is not a huge issue as long as the performance in all other ranges and at throttle transitions is good. But on D-jet.....poor idle makes for very finicky/sensitive tuning issues to the manifold pressure sensor that affects a broad range of performance.....but mainly throttle transitions.

Its not un-tunable.....just a lot harder.

I am thinking after reading your response.....that not worrying about equal length...but instead maybe just a more equal collector......may be a better/simpler train of thought. Ray
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PostPosted: Sun Apr 19, 2020 11:42 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

One more thing for use who need it it you retain proper carb heat.
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PostPosted: Mon Nov 16, 2020 12:48 pm    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

Gerrelt wrote:
Yep, old thread, but this thread helped me in modifying my stock muffler. So I wanted to return the favor.

I am modifying a stock muffler for my Alfa Romeo engined beetle.
For this I opened a Ernst NOS muffler, and because that is something not many people get to do, I filmed it.
Other people might find it handy if they decide to modify a stock muffler (or are just curious in what it looks like inside):

https://youtu.be/OQlmITr10R8

These images can be found in the video, but they might be interesting on their own too:

https://gerrelt.nl/muffler_inside/inside_VW_beetle_muffler_explanation.png
I found it funny that the sound comes from one peashooter, then both, then the other one, and then both again.

https://gerrelt.nl/muffler_inside/inside_VW_beetle_muffles_front_cylinder.png
A cone in a dome, pretty restrictive..

For my project, I removed the inner cones, and the tubing in the middle section (edit: because Alfa engine has exhaust outlet at the bottom, so shorter rear exhaust tubes). I also added holes to the dome, and the inner baffles.
I'll be using bigger pea-shooters too, with a bigger inner diameter.
It's not done yet, but I hope it will sound decent (=not too loud).


I made a video of the sound the modified exhaust makes. Be aware that it's not a VW beetle engine where it's bolted to, but a 1351 cc Alfa Romeo 33 boxer engine.
Take a listen:

Link

I am using larger then stock tail pipes, 32.5 inner diameter instead of the stock 21 mm.
The stock ones will probably make the exhaust a bit quieter.
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PostPosted: Mon Nov 16, 2020 1:08 pm    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

I gutted a stock muffler for my 1500cc 40hp and added quad tips. This muffler didn't have the internal pipes, just baffles. Sounds cool, might be a little too loud for a convertible.


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.




Link



Link

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PostPosted: Mon Apr 10, 2023 10:46 am    Post subject: Re: Cutting the Baffles from a Stock Muffler Reply with quote

Has anyone ever ( Ray maybe? ) done this to a late model 49 state fuel injected muffler, or seen the inside of one? I have an old one laying around somewhere that I can cut open, but need to find it first. The system supposedly flows better than a stock pea shooter unit, and I'm curious about the internal baffling. It could be a nice addition to my upcoming 1904cc build.
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