scoobydrvr Posted February 24, 2017 Share Posted February 24, 2017 Are there any exhaust design gurus on here? I took my car to the muffler shop asking for something capable of flowing the HP numbers I'm putting down but able to still remain relatively quiet. He was able to fit a 3" pipe matching my down pipe that Y's to dual MagnaFlow mufflers with a long, 20" resonator under that driveshaft. The drone this created at ~70 was pretty harsh so I took it back and had him fit different baffled-style mufflers that are much better but still drones at highway speeds. Two questions about this setup: Does anyone have a suggestion for eliminating the drone? Would the 3" pipe Y-ing into two 3" branches have any effect on the tone or flow? Link to comment Share on other sites More sharing options...
whitrzac Posted February 25, 2017 Share Posted February 25, 2017 Same boat, I'm assuming wagon? Try smaller Y section, maybe 2.25 rather than 2.5. Extend the tips past the edge of the bumperMake sure they're not pointing down. You can try welding in a high flow cat, it should cut down on a lot of the noise, but I haven't tried it yet. Link to comment Share on other sites More sharing options...
The 2Fiver Posted February 25, 2017 Share Posted February 25, 2017 Does anyone have a suggestion for eliminating the drone? Would the 3" pipe Y-ing into two 3" branches have any effect on the tone or flow? Are you sure the Y-pipe has two 3" branches? This would make things incredibly loud. The magnaflow mufflers are glorified resonators so changing them out was probably the most helpful in dialling down the drone. I found that welding in a resonator got rid of the rattles pulsing through the panels at different RPMs. After time, it broke in and the vibrations have disappeared. like Whitrzac said, a catted downpipe will help too. My turboback (Cobb carted/magnaflow) only starts to drone on steep inclines at speed, cruising is fine. As for your next step, try and line the trunk with dynamat? Link to comment Share on other sites More sharing options...
scoobydrvr Posted February 25, 2017 Author Share Posted February 25, 2017 Thanks for weighing in guys! FWIW my down pipe is catted and I'm quite sure the pipe after the Y is 3". The installer was quite proud of getting them to fit and made sure I knew that's what he did. I asked a mechanical engineer buddy of mine about what a 3" -> 3" Y would do to the flow. He said he's not sure but, for proper flow they should be 2.25" branches. I wondered if this might be part of the problem... If I took it back and had him replace the pipe, would the be an issue with using the 3" inlet mufflers? I've already spent so much on this system... Link to comment Share on other sites More sharing options...
rhino6303 Posted February 25, 2017 Share Posted February 25, 2017 I would have a 3" vibrant ultra quiet resonator installed. They are superior to the bottle resonators. Link to comment Share on other sites More sharing options...
The 2Fiver Posted February 26, 2017 Share Posted February 26, 2017 I asked a mechanical engineer buddy of mine about what a 3" -> 3" Y would do to the flow. He said he's not sure but, for proper flow they should be 2.25" branches. I wondered if this might be part of the problem Correct, there's no need to run 3" to the mufflers. I don't know if you want to mess around with a 2.25" a 3" adapter on them because it could affect the fitment of the muffler tips relative to the bumper cutouts. Then again, it's a custom setup so I'm sure They could be modified to suit. Just taking a shot in the dark, most 400 whp LGTs' would probably run a single catless 3" system out the left. Not sure what kind of numbers you're shooting for. Consider getting a proper LGT axelback to replace your magnaflows. There is little to baffle sound in the mags, you can pretty much see through the other side. Link to comment Share on other sites More sharing options...
scoobydrvr Posted February 26, 2017 Author Share Posted February 26, 2017 Thanks for the input everyone! @rhino6303: What makes the Vibrant system superior? I'm not familiar with the product. @The 2Fiver: I'm currently sitting at ~325 to 350 (digital virtual dyno makes it kinda hazy) but had to hold off on more tuning when my MAF started maxing out. I'm not hell-bent on hitting a particular number, just getting what I can out of the setup I've got; if that means I lose some ponies because my exhaust is restrictive, I'm okay with that. Ultimately my goal is to have a sleeper of a sedan that I can take my soon-to-be-born son in and not damage his hearing. FWIW, I've already had the shop switch the mags out for baffled mufflers that made things a little better but didn't completely solve the problem. On a related note: I've got two 3" in/out offset Magnaflow mufflers for sale. Less than 1000 miles on them ;-) Link to comment Share on other sites More sharing options...
rhino6303 Posted February 27, 2017 Share Posted February 27, 2017 Thanks for the input everyone! @rhino6303: What makes the Vibrant system superior? I'm not familiar with the product. Regular bottle resonators generally have a perforated tube surrounded by a fiberglass insulation. The vibrant ultra quiet has a larger chamber and more insulation. I believe the larger chamber cancels/bounces sound waves better than the small tube. It's similar in the idea of a large chamber oem muffler. Link to comment Share on other sites More sharing options...
scoobydrvr Posted March 6, 2017 Author Share Posted March 6, 2017 Well, after a 4th trip to the muffler shop (wasn't charged this time, thankfully) I still have the drone. I had him take the Y pipes down to 2.25" as suggested and it helped significantly under 40 but the drone is still present (albeit not as loud) under acceleration or deceleration around 3k. I guess I'll be looking into the vibrant resonator. rhino6303: Is this the style you were referring to (because they also offer a bottle-type)? https://smile.amazon.com/dp/B001806YE2/ref=psdc_15713921_t3_B000E3VHWI Link to comment Share on other sites More sharing options...
rhino6303 Posted March 6, 2017 Share Posted March 6, 2017 Well, after a 4th trip to the muffler shop (wasn't charged this time, thankfully) I still have the drone. I had him take the Y pipes down to 2.25" as suggested and it helped significantly under 40 but the drone is still present (albeit not as loud) under acceleration or deceleration around 3k. I guess I'll be looking into the vibrant resonator. rhino6303: Is this the style you were referring to (because they also offer a bottle-type)? https://smile.amazon.com/dp/B001806YE2/ref=psdc_15713921_t3_B000E3VHWI That's the one. Link to comment Share on other sites More sharing options...
scoobydrvr Posted March 15, 2017 Author Share Posted March 15, 2017 Okay, just drove 4 hours and my ears are really tired... I've changed over to a baffled muffler, installed the Vibrant resonator, and dropped the pipe size after the Y to 2.25". All of these made a big, big difference but didn't eliminate the drone. I'm out of ideas and so is the guy at the muffler shop. Is there a muffler out there that is quiet but still flows well? Would a pair of STP/STi units flow sufficiently but knock down the noise? Link to comment Share on other sites More sharing options...
bigleben Posted March 15, 2017 Share Posted March 15, 2017 Been running with varex mufflers ( http://www.xforce.com.au/products/varex-mufflers ) for the past 3-4 years and really love them. Expensive since you need to fab the piping + flange but IMO worth it. It's rather quiet when closed ( 3" catted DP + TurboXS Midpipe + 2.5in/out mufflers) and loud when you need it. You can have a conversation with the back passengers without shouting. Look in the soundclip sticky, I posted a clip when it was on my LGT. Link to comment Share on other sites More sharing options...
scoobydrvr Posted March 16, 2017 Author Share Posted March 16, 2017 Dude, you weren't joking about the price of those. $400/each! What are the thoughts on the twin loop mufflers? Link to comment Share on other sites More sharing options...
Infosecdad Posted March 16, 2017 Share Posted March 16, 2017 Okay, just drove 4 hours and my ears are really tired... I've changed over to a baffled muffler, installed the Vibrant resonator, and dropped the pipe size after the Y to 2.25". All of these made a big, big difference but didn't eliminate the drone. I'm out of ideas and so is the guy at the muffler shop. Is there a muffler out there that is quiet but still flows well? Would a pair of STP/STi units flow sufficiently but knock down the noise? In my experience the WRX/STI mufflers drone on the LGTs, at least on my wagon. I liked the sound of the Nameless 5" mufflers, but they would drone on the highway. The HKS Silent Hi-Power that I have now have a good sound under acceleration, but as you get up to cruising speed, they quiet down. Cruising at 70-80 mph is quiet as stock, it's nice for long distance driving. They just aren't easy to find a set. The rest of my exhaust is Invidia catless up-pipe, Invidia catted downpipe, and stock midpipe connected to the HKS Silent Hi-Power. Link to comment Share on other sites More sharing options...
rhino6303 Posted March 16, 2017 Share Posted March 16, 2017 Have you ever thought of welding in a j pipe resonator? You can record the frequency when the drone occurs and calculate the length of exhaust needed to "cancel" the frequency. Link to comment Share on other sites More sharing options...
scoobydrvr Posted March 16, 2017 Author Share Posted March 16, 2017 @Infosecdad: HKS Silent Hi-Power looks like a great solution but also looking at some serious coin to pick a set up... I've already put something like $700 into this setup trying to get it figured out. That'll have to be an option of last resort. @rhino6303: I've considered the j pipe option suggested by a Honda buddy of mine; I'll look into it a little more closely and see what my options are. I've also considered building a crude noise cancelling circuit and wiring it up to a subwoofer. I can't make it as sophisticated as something like a Bose system (there's a reason those guys are so successful: it's HARD!) but I should be able to get something working. I know the problem frequency range is between ~60Hz and 150Hz so it's a perfect range for that. Plus, I'll finally have an excuse for installing the subwoofer I've been wanting. However, after digging around in this site I found a thread from 2010 for the Bosal SPT V1.5 systems that were being sold and, I'm pretty convinced my problem can be solved with either a better muffler or better tubing. That system as NO resonator on it and received rave reviews from those who bought it. So either the muffler is built differently or the tubing on my car is some really thin, light, cheap stuff that "rings" easily. There's no telling if the link is still good but I'm going to try emailing Mike to see if I can pick his brain; maybe he has a suggestion/solution or maybe he'll just sell me a couple mufflers... Link to comment Share on other sites More sharing options...
Running_riot Posted March 16, 2017 Share Posted March 16, 2017 Resonance tubes. If youve never looked at the exhaust system on an S2000, that's the best way to go. It's basically a separate tube that goes in the opposite direction of exhaust gas and it cancels out the bass of the exhaust (source of the drone) S2000 example. See the pipe jutting out at the collector? Tanabe example on 370Z, see them hanging out by the cans? This is a muffler delete from AA for BMWs. See the mushroom looking thing? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Running_riot Posted March 16, 2017 Share Posted March 16, 2017 They're also called Helmholtz chambers. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Running_riot Posted March 16, 2017 Share Posted March 16, 2017 They're also called Helmholtz chambers. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
scoobydrvr Posted March 16, 2017 Author Share Posted March 16, 2017 That's been suggested, and thank you for the info. According to a random Reddit thread (for what it's worth) I'll need an 18" piece of tube for the frequencies I'm getting. ((343)/(RPM * 4 * (1/60))) / 4 - ((343)/(2800 * 4 * (1/60))) / 4 = 0.459 m or 18.085 inches I'm not sure where I'm going to be able to find 18" of perpendicular length under the car though. I'm getting conflicting information about the geometry of the tube though: "Must be perpendicular!" "As few bends as possible!" "Any amount of bends just so long as they aren't too sharp!" "No bends more than 90!" Any thoughts on this? Linky I'm not sure how I feel about his frequency calculation because I observed the problem frequencies to be between ~60Hz and ~110Hz during a sweep through the same RPM. The provided formula says they should have been 186.6 Hz... Maybe I should borrow a high quality microphone and run an analysis through Audacity or something. Link to comment Share on other sites More sharing options...
scoobydrvr Posted March 16, 2017 Author Share Posted March 16, 2017 That's been suggested, and thank you for the info. According to a random Reddit thread (for what it's worth) I'll need an 18" piece of tube for the frequencies I'm getting. ((343)/(RPM * 4 * (1/60))) / 4 - ((343)/(2800 * 4 * (1/60))) / 4 = 0.459 m or 18.085 inches I'm not sure where I'm going to be able to find 18" of perpendicular length under the car though. I'm getting conflicting information about the geometry of the tube though: "Must be perpendicular!" "As few bends as possible!" "Any amount of bends just so long as they aren't too sharp!" "No bends more than 90!" Any thoughts on this? Linky I'm not sure how I feel about his frequency calculation because I observed the problem frequencies to be between ~60Hz and ~110Hz during a sweep through the same RPM. The provided formula says they should have been 186.6 Hz... Maybe I should borrow a high quality microphone and run an analysis through Audacity or something. Link to comment Share on other sites More sharing options...
Running_riot Posted March 17, 2017 Share Posted March 17, 2017 I read another formula. Something about an adjacent tube to the cans being twice the length of the exhaust tips. I saw it on Google in the hot rod forums. I googled Helmholtz chambers and it popped up in the search results. Also a thread from the GM forum for how to make your own Helmholtz chambers Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Running_riot Posted March 17, 2017 Share Posted March 17, 2017 I read another formula. Something about an adjacent tube to the cans being twice the length of the exhaust tips. I saw it on Google in the hot rod forums. I googled Helmholtz chambers and it popped up in the search results. Also a thread from the GM forum for how to make your own Helmholtz chambers Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Running_riot Posted March 17, 2017 Share Posted March 17, 2017 http://www.performancetrucks.net/forums/gm-engine-exhaust-performance-21/how-build-exhaust-resonator-tube-eliminate-drone-489463/ Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
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