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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Stock Muffler Eval & Upgrade /cgi-bin/YaBB.pl?num=1526453881 Message started by DragBikeMike on 05/15/18 at 23:58:01 |
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Title: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/15/18 at 23:58:01 This post will take awhile. I have lots of pictures to insert and it will take me multiple replies to complete. Please hold off on any comments until I finish the initial portion of the thread so it will make sense. I will state that I’m finished with the initial report when I finish up. I wanted to evaluate and test the stock muffler to see if I could improve the flow without dramatically increasing audible noise. I also want to be able to return the thing to stock condition if possible, so I will be doing any modifications in stages, testing for flow and noise level after each stage is complete. Todays post covers stage I. I was able to reduce the restriction from 35” H2O to 29” H2O. It’s still very quiet (pretty much like stock). It runs good. It was inexpensive to modify. It looks pretty much the same. It was quite a bit of work (but don’t forget I was doing lot’s of inspecting & measuring & testing along with the mods). It’s not as easy as installing a Dyna muffler. What I did was similar to the “Hartman Modification” discussed in the tech section. You can find more details on that mod at jonline.org/savage/Tips. The difference between the Hartman Mod and the DBM mod is I stick to the stock flow path through the muffler. I don’t claim that this is any sort of “tuned” system, it’s simply less restrictive. I know most of you have no interest in utilizing the stock muffler. Some think it is ugly. Others don’t care for the sound. Some are concerned with the weight. I personally find the animal a thing of beauty. Not necessarily because of how it looks (however I do think it looks pretty good), but because of the potential associated with it’s volume. It’s very large, much larger than say a Harley Dyna unit, or a SuperTrap. If you do a mathematical evaluation of just the cylindrical portion of the stock LS muffler (4.15” OD x 11” long) to just the cylindrical portion of the Dyna muffler (3.25” OD x 13” long) you will see that the LS muffler has 41 cubic inches more internal volume than the Dyna. Peek inside of the mufflers and you will see that the conical section of the LS muffler has way more volume than the Dyna. Also, keep in mind that Harleys (most models) use exhaust systems where each cylinder shares two mufflers. They use a crossover pipe so that each individual cylinder is actually connected to two mufflers. I think that the volume of the muffler makes a significant difference in how well the device can do it’s job (allow maximum flow while effectively attenuating noise). That extra volume allows the hot gasses to accumulate without building up excessive pressure. There’s nominally 500 degrees of crank rotation before the next slug of hot gas comes down the pike so that extra volume is a nice place to store the stuff while it meanders out the back door. Next time you pull up behind one of those new racy Camaros, take a look at those two, beautiful, stainless steel works of art hanging under the car. They are huge. How about any of those late model sport bikes like say a Hayabusa, GSXR, ZX-10, R1 or RR1000. They all have very large-volume muffler systems. Totally stock, those machines all make big horsepower and are quiet. Buell designed the eighth wonder of the world when he came up with that magnificent (albeit not too pretty) 55 gallon drum hanging off the bottom of the engine. It received accolades from the motorcycling press for affording excellent performance and lowering the center of mass while meeting federal noise standards. It also had this innovative valve system that opened up additional portions of the muffler under WOT conditions. Majorly cool Erick. Now corvette just happens to have a valve system like that. I’m not a muffler designer so I just sort of made up my own names for the various components. Please forgive me if the names I assigned turn out to be in disagreement with the actual name of a particular part of the muffler. Let’s get started. |
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Title: Re: Stock Muffler Eval & Upgrade - Stage II Post by DragBikeMike on 05/16/18 at 00:00:33 I removed the muffler and hooked it up to my poor man’s flow bench. The stock muffler restricted flow enough to register 35” H20 on the water manometer (almost pulled it right off scale). It was the same with or without the header pipe. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:01:40 Let's try that image again. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:02:58 I also did a similar test to a Dyna muffler (catalyst version). It registered 27.5” H2O. Sorry, I don’t have a non-cat version but I’ve heard they flow about the same. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:04:27 I reinstalled the muffler and cut it open using a 2-1/2” diameter hole saw. This required that I make a plug to go in the tailpipe so that the hole saw stayed on center. I learned that the plug must be a drive fit. A push fit allows the plug to back out of the hole and the saw to run away. I nicked my chrome a bit. I did the saw cut with the muffler installed since it held everything nice & steady. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:07:50 I noted one post in this forum where the member simply drove a wooden dowel into the tailpipe and drilled/sawed away. Here’s what came out. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:09:10 Here’s what I saw inside from the rear. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:11:04 I removed the muffler and did a thorough visual & dimensional inspection. Here’s a detailed sketch of the interior. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:14:31 There are three chambers (X, Y & Z) separated by solid plates (B, C & D). Small ¾” diameter tubes transfer the hot gasses between the chambers. There are two perforated plates (like really perforated, kinda like a screen they’re so perforated) that appear to be used to diffuse the hot gasses as they pass across the plate. I labeled the perforated plates (A & D). Be aware that there are two details missing from the sketch. There is some sort of diverter/deflector contraption just forward of the attenuation tube. It appears to be intended to help channel the hot gasses into the tube as they change direction from moving forward to moving toward the rear. There are also two holes about 5/16” diameter, one in solid plate “B” and one in solid plate “”C”. These small holes are on the periphery of the solid plates. They effectively short circuit the plate, but they are very small so it is probably a very whimpy short circuit. I immediately noticed that the actual muffler did not agree with the sketches provided in the post for Hartman Mod. The sketches had some features that were sort of like what I was holding in my hands, but they really weren’t close to the actual design. Based on what I could see, it looked like I might be able to make some significant improvements without increasing the noise level too much. Here is the flow path. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:18:36 Hot gasses enter the muffler at chamber “X” where they pass through perforated plate “A”, collide with solid plate “B” and make the first direction change. Then they enter transit tube 1 and move aft to chamber “Z”. Once in chamber “Z” they pass through perforated plate “D”, collide with solid plate “E” and make the second direction change. The gasses then move back forward and again pass through perforated plate “D” and into transit tube 2. They continue moving forward through the transit tube and enter chamber “Y”. In chamber “Y” the gasses collide with the backside of solid plate “B” and make the third direction change. The gasses then head aft again and enter the attenuation tube. This tube has a perforated section surrounded by a chamber. I call it the attenuation chamber. The acoustic energy diffuses through the perforations and enters the chamber where I assume it gets attenuated. The hot gasses continue aft and out the muffler to the atmosphere. No wonder its quiet. I believe that each time the hot gasses pass through a perforated plate, collide with an immovable object, change direction, squeeze through a tube, or disburse through an attenuation device, acoustic energy is diminished. If my guess is correct, the key to better flow without excessive noise is to provide a less restrictive path while maintaining the collisions, turns, squeezing, disbursement and attenuation. The low hanging fruit here is the attenuation tube. It’s relatively easy to remove. Its relatively easy to replace with a larger tube. Its relatively easy to reverse course and restore to stock if the mod doesn’t work as intended. Unfortunately, it’s at the very end of the flow path. If I want to capitalize on the volume of the muffler, I probably should be making improvements at the beginning of the flow path (transit tube 1). But until I have a better idea as to what effects various alterations will have on noise, I figured I should stick to stuff that is easily reversed |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:22:48 I tested the muffler with the entire attenuation tube removed. The restriction was reduced significantly. Now the poor man’s flow bench registered 26.5” H2O (1” less than Dyna). So how loud is it. I reinstalled the muffler and ran it. Whoa! Yuk! Waaaaaay too loud. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:27:06 I scrounged up some materials to fabricate a new attenuator tube with a larger inside diameter. One-inch electrical conduit looked like it would fit the bill. It has an inside diameter of 1-1/16” and an outside diameter of 1-3/16”. A ten foot section is about $11 (sorry, they don’t sell short sections). The stock attenuation chamber has an outside diameter of 1-1/2”, so now I needed some material with 1-1/2” outside diameter. I could find it on the internet from all sorts of mail order outfits like Summit, J.C. Whitney, Advanced Auto, etc. But I couldn’t find any locally. What I did find was a Moen handicap hand rail for a shower stall. Its stainless steel, exactly the right outside diameter, and very thin wall (which will allow lots of room between the inner & outer components of the chamber). It was like $20. What the heck, I’m on a mission. I bet you guys and gals on the mainland could scrounge this stuff up for a fraction of what I paid. I have plenty of old aluminum stock laying around from previous projects so I started by making a new end cap with a 1-1/16” hole (same as the conduit ID). Tried it with just the end cap. Better, but still way too loud. Flow test with just the new end cap pulled 28” H2O |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:41:44 Then I cut off a 7-3/32” section of the conduit and counterbored the end cap to provide a nice fit. So now when I installed the end cap the conduit ran from the end cap all the way to solid plate “C”. It would be pretty close to the stock flow path. I ran it again. Better, but still too loud for me. Some of you might find this configuration to your liking, but it’s too loud for me. Flow test in this configuration pulled 31” H2O. The restriction was higher because now the flow bench had to pull the air all the way through the stock flow path and the existing hole in solid plate “C” was only a little over ¾” diameter. Here's a sketch of that configuration. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:45:36 So now it’s the moment of truth. Do I hog out solid plate “C” to 1-3/16” so that the conduit can pass through to chamber “Y”. I can still restore to stock configuration by simply fabricating a bushing to slip over the stock attenuator tube. Go for broke. I used a step drill to enlarge the hole in plate “C” to 1-3/16”. Now its setup for a new, larger attenuator tube assembly. Here is a pic of the step drill. Using a Ryobi cordless worked nice because I could adjust the clutch so that it didn’t rip the plate up if the bit snagged. It made a beautiful hole. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:46:36 Here is a pic of the new 1-3/16” hole. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:48:35 I cut off a new section of conduit 8-5/16” long and perforated it over a 4-1/2” section. I attached that to the new end cap with some 10-24 stainless steel screws. I did an additional counterbore in the end cap to accommodate the 1-1/2” stainless tube that will serve as a chamber. Then fabricated a collar to hold the stainless tube in place and centered about the conduit. I don’t have any photos but I wrapped the perforated portion of the conduit with about seven or eight layers of stainless steel screen (a hot commodity in my neck of the woods) before I slipped the 1-1/2” stainless tube over the perforated conduit. Here is a pic of the completed assembly. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:49:34 Here is a pic of the individual pieces except the screen. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:50:36 Here is a pic looking through the stock tube and the new tube. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:51:51 Here is a pic showing the major difference in diameters. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:52:53 Here is a pic of the little dog ears I used to hold it all together. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:55:05 Flow test of the completed muffler showed a decent improvement. Now it pulled 29” H2O, a six-inch improvement. With the muffler back on and the engine running it seemed just as quiet as the stock muffler. The frequency of the exhaust note seemed a bit lower but the audible volume seemed just like stock. Very quiet, just what I was hoping for. Keep in mind that this configuration was quieter than just simply running an unperforated section of tubing from chamber “C” to the end cap, yet it reduced back pressure by an additional 2” H2O. Testing pays off. That attenuation chamber really works, it totally cuts down the audible energy. Here is a pic of the completed muffler prior to road test. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 00:56:37 The road test went very well. Very quiet, good power all around. No noticeable change in low end power. Nice hard pull up top. Just as quiet as stock under all conditions (idle, surface streets, accel, decel, freeway, WOT). No afterfire whatsoever. After the road test I removed the muffler to permanently install the new attenuator tube. I painted the end cap with VHT to make it look as close as possible to stock. When I reinstalled it, I sealed it with a bead of high-temp RTV. Here is a pic of the finished product. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 01:00:44 I believe this would hold up better if I made the end cap and collar from steel rather than aluminum. I wasn’t sure how it would work and I hate making steel chips on my little lathe. If the aluminum fails, I’ll make some new parts from steel. I also think that a resourceful wrencher could fabricate something equivalent to this just using regular tools (hand drill, hack saw, jig saw, grinder, files, etc.). The materials are cheap. I’m sure conduit and universal exhaust tubing are cheap and plentiful in the continental US. Tip 1: The muffler clamp bolt is really humbug to access when the head of the bolt faces up. Turn the clamp over so the bolt head faces down. Then you can easily access from underneath the muffler. You will have to bend an orientation tab flat but it’s very easy to do. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 01:02:06 Tip 2: The sharp edges of the passenger peg assembly chew up the chrome plating on the muffler as you wiggle the muffler around trying to get it off the header pipe. Wrap the peg assembly with tape to protect the finish on your very stylish muffler. [img][/img] |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/16/18 at 01:09:04 The next stage of this project involves figuring out a way to provide an additional, or larger, flow path from chamber “X” to chamber “Z” without allowing significant leakage into chamber “Y”. Either replacing transit tube 1 with a larger transit tube, or putting in an additional tube, will accomplish this goal. This particular change would capitalize on the volume of the LS muffler (the feature that enamored me to this muffler in the first place). The final stage would be to figure out how to provide an additional, or larger, flow path from chamber “Z” to chamber “Y”. Essentially, I want to maintain the stock flow path to scrub off the noise. I hope this post provides some useful info for any of you who are contemplating modifications to your stock muffler, mods to some other muffler, or changing to a different muffler. At least you will have a better understanding of what’s inside the stock muffler and the flow path. If you have any good ideas, LMK. BTW, I already got all the ideas about “simply installing a Dyna muffler” or “just put a Trap on it” or “the Jardine works sweet” etc. Remember, I want it to look and sound as close to stock as possible. This concludes my initial post. Comments are welcome and encouraged. Aloha Mi Amigos |
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Title: Re: Stock Muffler Eval & Upgrade Post by Dave on 05/16/18 at 04:26:39 That is quite a science project - well done! I agree that a pleasant exhaust tone and a lack of "noise" from the exhaust makes for a very peaceful ride. The stock mufflers on the Savage and sport touring bikes I have owned do a really good job of quelling the exhaust pulses......all I hear is wind and a pleasant purr from the engine. I also agree that the larger the muffler volume - the more effective the muffler will be. There just isn't enough space in a small, compact, light muffler to dampen the pressure pulses and sound waves. Most of the new bikes have a "box" under the engine in series with muffler(s) on the side - or huge stand alone mufflers (the Indian Scout has obnoxiously huge mufflers that look really out of place on the bike). The smaller the muffler - the louder it will probably be. The small KTM 390 bikes have mufflers that make them sound like weed wackers! I have been "eyeing" take off mufflers on eBay from sport touring bikes like the BMW RT's, Honda ST's, etc. - adapting one of them could be easier than modifying a muffler for most folks without a lot of fabrication skills and tools. |
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Title: Re: Stock Muffler Eval & Upgrade Post by Papa Bear on 05/16/18 at 19:04:36 Has anyone tried a V-rod muffler ? |
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Title: Re: Stock Muffler Eval & Upgrade Post by eau de sauvage on 05/16/18 at 20:02:23 To my eyes the savage stock muffler is incredibly ugly and moreso on a svelte bike like the S40. I love the way the dyna is not only narrower but tapers down to a small diameter exit. Might be a lot of work but have you thought of tapering the end of the pipe down to a smaller exit? As for noise, to each their own of course but I really disliked the sewing machine sound of the stock muffler, although I do like the buttery smooth sewing machine sound of my Bernina 730 record sewing machine! I find that when cruising that wind noise can be deafening and tiring, whatever type of helmet so when on a tour I'll use ear plugs anyway. |
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Title: Re: Stock Muffler Eval & Upgrade Post by batman on 05/17/18 at 09:16:16 It's hard for me not to like a Dyna. My stock muffler rusted out ,and replacement cost was over $300, I went to the nearest HD dealer and bought 3 Dyna and two HD clamps for $15 . The Dyna weighs less ,sounds a bit deeper, and isn't very much louder , at steady speeds , and just a bit louder at WOT . After 4 years it doesn't show any rust (good chrome) and with a slight rejet the bike runs stronger. I like the look much better than stock. The crossover on the Harley,s helps them produce low rpm torque ,which they need ( how do you get a bike that weighs 800lbs with two riders up a steep hill?) |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/17/18 at 17:51:28 Good comment about the V-Rod muffler Papa Bear. It might be an excellent candidate. I believe there is a V-Rod model that is called the "Street Rod" (hope I have that right) that uses a nice big turned out can on each side of the bike. They have a cool looking flame spray coating. They certainly have enough size. The big FL touring bikes are also supposed to make several more ponies than say a Softail or Dyna. The increased power is supposedly due to the larger mufflers. Hey Dave, I'm not too familiar with the models you mentioned in your post. Are they in-line fours? If they are, I personally think you would be better served by a take-off unit from something like a BMW cop bike (1100cc opposed twin) or some other BMW that uses a boxer engine, or possibly something off one of these new Yamaha FZ vertical twins, or maybe even that Yamaha Bolt. They're all mufflers that have to service two large displacement cylinders rather than four small displacement cylinders. Nothing like a fun project with lots of twists & turns to keep you young. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/18/18 at 17:38:14 I scrounged up two more mufflers for comparison. A stock Harley muffler from a 1990 FLSTC (Heritage Classic) and a Supper Trap for a Harley Softail. The stock Harley unit is pre Catalyst and it did not flow as well as the Dyna unit with a catalytic element. I tested the SuperTrap with several disc combinations. Here's a pic of the Heritage unit under test. It pulled 31" Hg. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/18/18 at 17:47:09 Here's a pic of the SuperTrap. With 21 discs it pulled a measly 13" Hg, best so far. Beats all others in the flow department. With 14 discs it pulled 14.5 " Hg, and with 7 discs it pulled 17" Hg. So even with only 7 discs it still flows much better than all others. I ran these mufflers on my Harley about 20 years ago. They were too loud, and I even flunked safety inspection with them. I had to go home and install the stock exhaust system to get my safety sticker. The inspector was a jerk, but what can I say, he was only doing his job. When I returned for reinspection he showed me a letter that the state had sent to all the inspection stations. The letter said SuperTraps were considered "cutouts" because you could remove the disc element. Those mufflers were a bit too loud for me, but they were quieter than any other system I ran on that bike. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/18/18 at 17:48:43 Look what I found in my junk pile. I think this is a perfect chunk of tubing for Stage II. |
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Title: Re: Stock Muffler Eval & Upgrade Post by Dave on 05/18/18 at 17:55:28 When I bought my Savage it has a Supertrapp on it - it was too loud for me and I liked the Dyna muffler that replaced it. |
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Title: Re: Stock Muffler Eval & Upgrade Post by batman on 05/18/18 at 23:05:30 Dave , Did you notice any difference in high speed performance between the two mufflers? Are we talking about your café bike ? Are we talking about before or after the high comp. piston and cam? |
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Title: Re: Stock Muffler Eval & Upgrade Post by Dave on 05/19/18 at 04:07:19 7271647D717E2428100 wrote:
When I bought my used Savage it had 262 miles on it, and it was stock except for the Supertrapp. I don't ever remember challenging any high speed with the bike, as I didn't like the seemingly high rpm that the low gearing imposed......65 mph was about as fast as I can remember riding it. |
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Title: Re: Stock Muffler Eval & Upgrade Post by batman on 05/19/18 at 07:24:19 Dave , I didn't mean top speed ,I simply meant ,did you notice any difference in performance generally . did the bike seem to prefer one over the other ? ( just looking for a " seat of the pants" opinion). |
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Title: Re: Stock Muffler Eval & Upgrade Post by Dave on 05/19/18 at 12:50:58 Nope....my seat aint' all that sensitive. |
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Title: Re: Stock Muffler Eval & Upgrade Post by ruckus430 on 05/21/18 at 10:14:18 But did your mods remove the whistling sound from the stock exhaust? thats the main downside about the stock ones. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/21/18 at 23:39:23 I didn't note any whistles before I started on the mod, and I don't hear any whistles after. The acoustic frequency seems a bit lower but the volume seems about the same as stock. It's very quiet, and it looks stock. I'm currently working on the second stage. I have what I think is a good idea and intend to start on that in a few days. Goal remains the same, more flow without appreciably increasing noise. You can't make good power without good flow. |
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Title: Re: Stock Muffler Eval & Upgrade Post by batman on 05/22/18 at 14:38:03 DBM, Is there a point were good flow, may become to much flow ? |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/23/18 at 02:38:24 I personally don't believe so, at least not with this muffler. Maybe a glass pack with a straight through flow path the same diameter as the header could be interpreted as "too much flow". I often hear stuff like "you gotta have some backpressure". I think its more like you need some junk in the flow path to break up the acoustic waves and prevent harmonic reversion. I don't think I've ever seen a maximum effort engine using mufflers unless mufflers were required by the sanctioning body. Top fuel dragsters run open headers. With this stock muffler I believe I can achieve a significant increase in flow, and that should permit the other components like the airbox, carburetor and head to do their job better. I want to achieve that while maintaining low levels of noise. I will have to retain all the twists and turns and collisions and attenuation. If I don't, it will be too noisy. The torturous flow path will break up the acoustic waves so I shouldn't have problems with reversion. Even if I fail, I'm still gonna have fun with it, and I will learn a lot of really good stuff. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/30/18 at 23:39:16 For Stage I of the modifications I grabbed the low hanging fruit, the attenuation chamber & tube. I made that decision because those components had to be removed in order to inspect the interior of the muffler and figure out the flow path, and those components were easiest to restore to the original configuration if things didn't work out as planned. I mentioned earlier in the post that, in my opinion, the best place to make improvements was in the flow path between chamber "X" & chamber "Z". Making those two chambers available to hot gas flow and expansion takes advantage of the muffler's large volume. Using that large volume to store the expanding gasses and allow them to exit gradually between exhaust events keeps the pressure in the exhaust system to a minimum. There's around 500 degrees of crank rotation between exhaust events. A muffler with more volume can store the exhaust gas and allow it to bleed off, which prevents the back pressure from increasing. As the engine RPM increases there is less time between exhaust events so the ability of the exhaust system to store the hot gasses becomes more important as RPMs increase. The obvious solution was to increase the flow rate between the first and second chambers in the flow path ("X" & "Z"). There really is no practical way to make an internal improvement to that flow path. So I decided to make an external connection between chambers "X" & "Z". As it turns out, that was easy to do. Here is a sketch of the improved flow path. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/30/18 at 23:44:36 I found that 3/8" pipe elbows match up perfectly with 5/8-18 UNF bolts. I was able to buy a box of 25 bolts from Grainger for a whopping $2.35. That's right Ladies & Gents, two dollars and thirty-five cents. Go figure that one. Two 3/8" black iron pipe elbows (90 degrees) set me back $4.24 at Lowe's. Here's a shot of those Grainger bargain basement bolts. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/30/18 at 23:48:10 I attacked the muffler by first using a 1" hole saw to cut through the heat shield at the front portion of the muffler at chamber "X". Then I used a step drill bit to make a 11/16" hole through the wall of the muffler. Here's a pic of that portion of the mod. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/30/18 at 23:50:44 Then I made a 11/16" diameter hole with a step drill at the rear portion of the muffler just aft of the perforated plate. The step drill is the way to go, it works great. Here's a pic of that hole. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/30/18 at 23:58:56 The pictures and sketch should provide you with a general idea where the mods are done. I drilled through two of the 5/8-18 UNF bolts with a 7/16" bit. To make things fancy I cut back the undersides of the bolt heads so that the corners of the hex head don't contact the interior of the muffler and prevent a decent seal. Then I bored out one side of each 90 degree fitting to accept 1/2" conduit. I wanted to set it up with a slip fit to accommodate expansion. Here's a pic of the fittings & bolts. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:00:00 Here's another shot of the modified hardware. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:12:30 Once I had the hardware fabricated, I cut a section of 1/2" electrical conduit to a length that would provide about 1/8" axial movement when everything was assembled. I wanted the conduit to be able to expand and contract without being restrained. I assembled the fittings and conduit and installed the end cap with attenuation tube. It was time for a sound test. I was concerned that the sound level would increase to a point that was unacceptable to me. Here is a pic of the assembly prior to the sound test. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:24:51 The sound test was great. Best as I could tell, the sound level was pretty much the same. So I knew adding the additional transit tube (3) from chamber "X" to chamber "Z" would not alter the sound appreciably. Now it was time to improve flow between chambers "Z" & "Y". That's pretty easy to accomplish. I wanted to try and keep the flow rates balanced so I calculated how many 3/16" diameter holes have a cross sectional area equivalent to the 7/16" diameter holes I drilled in the 5/8-18 bolts. It works out to about 5.4 so I drilled 5 holes 3/16" diameter through solid plate "C". This allows the hot gasses to transit from chamber "Z" to chamber "Y". It was very easy to drill the holes using a long 3/16" drill bit (12" long). I chose 3/16" because if I want to reverse the mod all I have to do is fill each hole with a #14 sheet metal screw. Here is a pic of the long drill bit. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:39:25 After I drilled the five 3/16" diameter holes in solid plate "C", I reassembled everything and gave it another sound test. It was a bit louder but still easily passed my personal evaluation. This thing is very quiet. Very, very close to stock. On the poor man's flow bench the backpressure registered at 27-3/4" H2O. So the backpressure was reduced an additional 1-1/4" H2O. I thought it would be more but I'm not gonna look any gift horses in the mouth. I took it for a road test and it was sweet. Very quiet, no afterfire, good power all around. It felt a little light on fuel so I upped the main jet to a 152.5. It really came alive after that. The modified muffler really compliments the airbox and cam. With everything working together this thing really scoots. It loves the freeway. Screw it on and it just goes. I love it. It might even be able to take a 155 main. Here's a pic of the modified exhaust with the extra transit tube. Ooops! Can't see the tube? That's cause it's pretty stealthy. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:40:39 Here's a pic at a different angle. You can see the transit tube peeking out. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:42:07 Here's a shot from down low. You get a good view of things from this angle. |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 05/31/18 at 00:53:04 So far, this line of modification has worked quite well. The sound level is still very close to stock. The power feels very good. There are no carburetion problems. It pretty much looks the same unless you bend down and take a peek. I like it. If you wanna keep your stock muffler, these mods will improve performance without making a bunch of noise. One very nice feature is the fact that the noise level is so low. When you screw on the throttle you get the sensation of acceleration without being biased by a bunch of thunder clap from the exhaust. It just loves the freeway with this setup. You can go WOT without attracting all sorts of unwanted attention. You don't alert every cop in the surrounding counties when you hit the wick. You don't scare the bejesus out of granny in the next lane when you blast off. Silent but deadly. Sweeet! |
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Title: Re: Stock Muffler Eval & Upgrade Post by DragBikeMike on 06/16/19 at 17:12:57 I'm pulling this old post forward so Junker can get a look at what's should be inside his stock muffler. |
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