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HighFlo Quiet Muffler Details (Read 658 times)
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HighFlo Quiet Muffler Details
12/30/20 at 17:58:33
 
In November of 2020 I did a muffler shootout.  It was fun and I proved that a free-flowing muffler can make a huge difference in performance.    Although the muffler I was running (modified stock muffler) flowed better than a stock muffler, it left a pile of horsepower and fuel efficiency on the table.  A free-flowing muffler was in order, but it had to be quiet.  As it turns out, it’s not too difficult to build a HiFlow Quiet Muffler.

The new HiFlow muffler is based on an automotive resonator.  It flows much better and is quiet as a church mouse.  It lobs a whopping 1.52 seconds off my acceleration time (3rd gear 4K to 7K) and gets 63 mpg in the bargain.  What’s not to like about that?  It’s cheap too.

This post provides the general details on the construction of a HiFlow quiet muffler.  Let’s get started.
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Re: HighFlo Quiet Muffler Details
Reply #1 - 12/30/20 at 17:59:36
 
The foundation for the HiFlow muffler is LCGP’s 2.5” stainless-steel automotive resonator, model 254019.   You can find one on Amazon for $36 bucks.  It’s a high-quality item, polished stainless steel, light weight, and has nice welds.
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LCGB_Part_Number_254019.jpg

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Re: HighFlo Quiet Muffler Details
Reply #2 - 12/30/20 at 18:00:17
 
Dimensions:
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LCGP_Muffler_Dimensions2.jpg

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Re: HighFlo Quiet Muffler Details
Reply #3 - 12/30/20 at 18:01:01
 
This shows the construction (structural analysis not so much, how it’s constructed yes).  It’s a straight through design, a full 2-1/2” all the way through.  It relies solely on absorption to attenuate the acoustic energy.  It’s packed with one layer of stainless-steel mesh and one layer of glass fiber cotton.  The packing is captured with a stainless-steel grid.
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LCGP_Muffler_Construction2.jpg

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Re: HighFlo Quiet Muffler Details
Reply #4 - 12/30/20 at 18:02:28
 
The design of the HiFlow Quiet muffler utilizes three methods of noise reduction: restriction, direction change, and absorption.  A baffle tube is used to restrict flow and force the hot gas to change direction.  The stainless-steel mesh and packing material in the LGCP resonator perform the absorption.  This illustration shows the flow path.
 
Hot gas enters the baffle at chamber “A”.   A plug in the center of the baffle forces the hot gas to turn and flow outward through perforations in the baffle.  The hot gas then enters chamber “B” where it turns again and flows toward the rear of the muffler.  Acoustic energy is absorbed by the packing that surrounds chamber “B”.  The hot gas then turns again and flows through the perforations in the baffle into chamber “C”.  Finally, the hot gas turns again and exits the baffle tube.  This system is highly effective at reducing noise.  It also flows well.  My tests show the restriction is low compared to a Dyna or a modified stock muffler.  In terms of flow, it rivals the Mac muffler, which is a very loud straight-thru design.
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LCGP_HiFlow_Muffler_Flow.jpg

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Re: HighFlo Quiet Muffler Details
Reply #5 - 12/30/20 at 18:04:12
 
The 2-1/2” core lends itself to installation of a large diameter baffle.  There’s plenty of room for the hot exhaust gas to flow out of the baffle and through the muffler.
 
During the muffler shootout I tried a baffle with a 1.52” ID.  It worked well but I wanted more flow.  So, the next iteration of the HiFlow design got a baffle with a 1.65” ID.  That seemed just about right.  On the test bench, the larger diameter baffle reduced the depression from 33-1/2” H2O to 31-1/2” H2O.  In comparison, the Mac chrome reverse cone muffler pulled 32-1/2”.

The area of the cross section of the baffle ID (“A”) must be close to the area of the cross section of the void between the baffle outside diameter (OD) and the resonator core ID (“B”).  If you use a baffle with a larger ID it reduces the cross section of the void.  So, if you increase the baffle diameter too much the void gets too small and flow is degraded.   The final cross sections were 2.14 in2 (“A”) vs 2.50 in2 (“B”).  That was close enough for me.

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Chamber_Cross_Sections_A_vs_B.jpg

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Re: HighFlo Quiet Muffler Details
Reply #6 - 12/30/20 at 18:05:15
 
The baffle is fabricated from a 1.75” tail pipe.  It has a 1.65” ID and a 1.75” OD.  It is 18” long.  This item came from AutoZone.  The AutoZone part number is 17621.
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Tailpipe_1_75_2.jpg

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Re: HighFlo Quiet Muffler Details
Reply #7 - 12/30/20 at 18:06:05
 
The size and number of perforations must be determined.  No sense making any more holes than necessary.  More holes equal more noise.  Test the baffle tube to determine the point where adding more holes doesn’t increase flow.  It’s a simple test.  Close off one end of the tube and start sucking on the other end with a test rig.  Two big shop vacs work well.  With 36 holes this one pulled 34-1/2” H2O.  Keep adding holes in increments of 12 until you see the improvement start to flatten out.  It looked like 108 holes on each side of the center plug would be the sweet spot.   Here’s a look at the baffle perforation test.
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Perforation_Tests_22.jpg

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Re: HighFlo Quiet Muffler Details
Reply #8 - 12/30/20 at 18:06:51
 
You can see on this graph that the curve starts to flatten at about 96 holes and it’s pretty much done by 120 holes.  I chose 108 holes for my sweet spot.  I think any more than 108 holes will only add noise, it won’t reduce back pressure or increase flow.  Each perforation was made with a 11/64” drill bit (about .17”).  It takes a while.
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Baffle_Restriction_Test_1_65_ID.jpg

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Re: HighFlo Quiet Muffler Details
Reply #9 - 12/30/20 at 18:16:47
 
While on the subject of back-pressure.  I hear a lot of banter about back-pressure and how your engine needs back-pressure and how exhaust systems with no back-pressure kill torque…..   I say baloney.  David Vizard has a great cliché.  “The best performance muffler is no muffler at all.”  Yes, you can screw up street manners with a straight pipe, but that’s not a result of no back-pressure.  It’s due to a resonant wave returning to the exhaust valve while the valve is still open.  All you need is something to break up the resonant wave (like a baffle or slight reduction in pipe size).   The baffle will inherently increase exhaust pressure a bit.  The trick is to come up with a system that can reduce noise, break up the resonant wave, and allow the highest possible flow.

This is a great video.  Engine Masters does some cool dyno testing on exhaust systems.  There’s a part in the video where they talk about back-pressure.  If you pay close attention you will see they are being sarcastic, joking about the back-pressure myth.  Ultimately, they prove how the less restrictive exhaust system is pretty much better everywhere.

The Power of 2.5- vs. 3-Inch Exhaust - Engine Masters Ep. 9 - YouTube https://www.youtube.com/watch?v=_PVXvHkr-Vs

Oh well, looks like the link won't work but I bet if you Google "Engine Masters Episode 9" it will get you there.
 
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« Last Edit: 12/31/20 at 07:51:15 by verslagen1 »  

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Re: HighFlo Quiet Muffler Details
Reply #10 - 12/30/20 at 18:21:04
 
This sketch identifies the various pieces needed to construct the LCGP HiFlow muffler.  Any similar glass-pack muffler could be used.  If you use a muffler smaller than 2-1/2” the baffle size will have to be adjusted accordingly, and the number and size of perforations will also need to be adjusted.  Anything larger than 2-1/2” and similar adjustments will be necessary.  I personally think that 2-1/2” is the optimum size for the LS650.   I use a Mac header pipe.  If you want to install the muffler on a different header pipe you will need to use a different reducer (item 7) to suit the header and you may need to bend or kink the reducer to accommodate the angle of your header.

Item 1 is the LCGP 2-1/2” Stainless Steel Resonator 254019   $36

Item 2 is the packing material (can’t be replaced)

Item 3 is the baffle tube, AutoZone 1.75” tailpipe 17621    $13

Item 4 is adapter bushing exit end, made from Lincoln 2” x 1.5” pipe bushing 440333    $13

Item 5 is baffle plug, made from Lincoln 1.5” pipe plug 440088    $6

Item 6 is adapter bushing inlet end, made from Lincoln 2” x 1.5” pipe bushing 440333    $13

Item 7 is exhaust reducer, 2.5” OD x 2.0” ID, ROL200ID250OD    $9

So, for $90 bucks and some elbow grease you can construct a quiet muffler that sounds great and hauls freight.
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LCGP_HiFlow_Muffler_Parts.jpg

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Re: HighFlo Quiet Muffler Details
Reply #11 - 12/30/20 at 18:21:54
 
Here is the raw material needed for the adapter bushings and the inlet reducer.  It’s all pretty much routine hardware.  The galvanized pipe bushings should be available at any hardware store, and the exhaust reducer is available at most auto parts store.
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Reducer__Bshgs2.jpg

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Re: HighFlo Quiet Muffler Details
Reply #12 - 12/30/20 at 18:22:55
 
The inlet adapter bushing is 2.53” OD by 1.85” ID by 3/8” thick.  It can be made from the pipe bushing I list or any other ferrous material you can scrounge up (pipe cap, large washers, scrap steel plate, scrap steel pipe, etc.).  It’s not critical.  It just has to keep the baffle tube centralized and block off exhaust gas from flowing around the baffle.  Here’s a shot of the rough-out.  
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Adapter_Bshg_Rough_Machine2.jpg

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Re: HighFlo Quiet Muffler Details
Reply #13 - 12/30/20 at 18:23:35
 
This is the finished inlet adapter bushing.  Note the chamfer.  This bushing gets permanently installed in the 2 x 2.5 reducer.  The chamfer is there to help guide and align the baffle tube when you slide it into the muffler.  The baffle tube has a slip-fit with the inlet adapter bushing to accommodate expansion.  The baffle will run hotter than the muffler body and it will expand more.  The slip fit lets it grow without causing any undue stress.
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Adapter_Bshg_Inlet_Complete2.jpg

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Re: HighFlo Quiet Muffler Details
Reply #14 - 12/30/20 at 18:24:17
 
Here is the inlet adapter slipped over the baffle tube.  Because of the female socket in the tailpipe, the OD of the pipe in way of the adapter bushing is 1.85” instead of 1.75”.
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Adapter_Bshg_Inlet_Rough_Fit2.jpg

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