I found this to be informative, and if anybody has exhaust drone, they may be looking for this info. Especially if they have custom exhausts and engine swaps. The whole linked thread has good tips
The only thing I wonder is on a Fiero with the short exhaust that wraps around the engine... is if the drone actually also comes from the engines soundwaves harmonizing with the exhaust note and pipe resonance. In which case exhaust wrap might actually help. ( besides firewall insulation.)
"The idea here is to reintroduce a sound wave into the exhaust that is 180° out of phase with your drone frequency. To do this, you build your resonator tube at exactly one-fourth the length of the resonant wave. By the time the sound wave enters the resonator tube, bounces off the end and re-enters the exhaust stream, the amplitude is exactly opposite of the drone frequency and will lower or eliminate the volume of the drone.
Simply put, it is a small piece of exhaust pipe with a flat capped end welded nearly perpendicular to the exhaust flow post-muffler that serves to take some of the resonant amplitude and shoot it back into the exhaust pipe out of phase with the resonant frequency "
Very cool writeup, it's nice to see some actual calculations being used for exhaust system design. I've been debating adding some resonators behind my muffler in my exhaust system to eliminate drone but only have about a foot of space on each side. Using those formulas and doing some basic algebra, if I round 1 foot to .3 meters... a .3 meter long resonator would theoretically cancel out a drone at 8232 rpm.
I guess I won't bother then!
[This message has been edited by Silicoan86 (edited 06-06-2016).]
Very cool writeup, it's nice to see some actual calculations being used for exhaust system design. I've been debating adding some resonators behind my muffler in my exhaust system to eliminate drone but only have about a foot of space on each side. Using those formulas and doing some basic algebra, if I round 1 foot to .3 meters... a .3 meter long resonator would theoretically cancel out a drone at 8232 rpm.
I guess I won't bother then!
These are not the drones you are looking for. Find the drone first my friend, find the drone first.
Here is another thread about the same solution. Most of the V8s need this extra section of exhaust to be just over 2' in length which becomes a little problematic to package, especially in a fiero. http://ls1tech.com/forums/c...ne-swaps-solved.html
However, since most use a single in, dual out muffler, the exhaust effectively splits off and the route on each side is probably long enough before it exits the tips to be effective with this. So if you install a cutout (within the exhaust tube to restrict flow) the proper distance on one side, then it should cancel out the drone on the other side while cruising, then open it when you plan on not cruising.
Darth Fiero did something very similar on Tom's LS4 (cutout shuts off 1 exit of the dual exit muffler unless running close to WOT), but he also downsized the tube on the open exit as well.
Actually, after a little more thinking about it, I think I actually do have room for this. I could add one of these right before the muffler with a 90° bend and basically lay it on top of or in front of the muffler.
This is so simple to do that I think I'm going to try it before I weld the trunk back together. My 3.4 DOHC swap has a significant drone around 2000 rpm that I'd love to eliminate.
From my research on reducing interior and overall exhaust noise on swaps, from my communications with other forum members and from my experience here is what I have found: 1. Choice of muffler makes a big difference. Flotech the loudest, Spintech better, Magnatech a bit quieter 2. The larger the pipes the louder the exhaust. A crossflow muffler with dual 2 1'2" outlets will be louder than one with dual 2" outlets 3. Exhaust tip resonators do help a little 4. Wrapping the exhaust lowers the sound (Olejoedads tip) -but it can shorten its life 5. Insulating the inside of the deck lid with Duramat acoustic material helps reduce interior noise. 6. Reportedly the insertion of an exhaust cone in the flow reduces sound levels. 7. The longer the system the lower the sound. Short (straight through) systems are the loudest. 8. Insulating the engine compartment, firewall and wheel wells will reduce interior noise. 9. An exhaust with a CAT will emit less sound than one without a CAT 10. Mufflers and pipes that physically touch the cradle will increase interior noise
In short it takes much work to have a quiet interior with a short engine swap exhaust
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 06-08-2016).]
If there's a lot of resonance and drone, you have to change something in the exhaust flow. It's like changing the tone of a "bell". You want to get the 'ringing' out.
Many install an inline resonator/bullet muffler in place of the catalytic converter. If you need muffler AND catalytic converter space is very limited. If you have a 3800 S/C install, your exhaust system is even shorter.
I'm looking a options for the Indy with Flowtech Afterburner muffler with catalytic converter. I have terrible drone at 2500-3000 rpm. Quiet above and below that when cruising.
Borla has a solution for their systems when customers complain of drone in their system. The Borla Venturi is a simple reducer that changes the flow characteristic and hence, the sound waves in the exhaust. People have said they WORK and experience no power loss (some complaints of power loss with C-C inserts). I'm expecting delivery next week. So I'll see how well they work after I install it.
Interesting, they actually affect drone? I wonder if it moves the drone higher or lower in the rpms? I do love more low end torque. SO they go in a header collector...
The Venturi Effect is something I show all the kids I know when they turn approx' 13-15....They are teenagers and begin to think "I KNOW it ALL!" so I ask them which way will two sheets of paper go, held approx' 1" apart, if I blow between them? Almost every one of them says they'll go out....And then they are amazed when the pages come together......"Don't think you know it all....You are young, and have a long life ahead- Continue learning- ALWAYS!"
Sadly, there are a lot of adults who could learn from this example.......
Here is another thread about the same solution. Most of the V8s need this extra section of exhaust to be just over 2' in length which becomes a little problematic to package, especially in a fiero. http://ls1tech.com/forums/c...ne-swaps-solved.html ...
This is really good info. What I found especially interesting is that the length of the J-pipe seems to have everything to do with creating the "null", to cancel out the drone, while, apparently, the diameter has very little to do with it, other than how much of an effect the j-pipe has. (Larger diameter equals more cancellation, if I read it correctly.) I've got a bit of a drone at highway speeds. It's never been a show stopper, but I may have to try this.
[This message has been edited by Raydar (edited 08-30-2017).]
I've always used cherry bomb glass packs, even a 12" one on a 5.2l dodge truck. They are loud the shorter they are but the bassy drone when cruising isn't there.
All of the exhaust inserts mentioned will decrease exhaust gas space and increase back pressure. The only one that says that it will not do it is the Dynatech Auger Style Muffler Straight Exhaust Pipe Insert. You insert it in a pipe and it reduces noise 6-7db.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 08-31-2017).]
All of the exhaust inserts mentioned will decrease exhaust gas space and increase back pressure. The only one that says that it will not do it is the Dynatech Auger Style Muffler Straight Exhaust Pipe Insert. You insert it in a pipe and it reduces noise 6-7db.
I'm liking to eliminate drone without making the exhaust note quieter.
[This message has been edited by 2.5 (edited 08-31-2017).]
Ive never experienced this drone everyone is talking about in at least 200 cars. My formula is luxury car is quiet, muscle or sports car loud. If this drone is meaning loud, just use bigger or more mufflers. I just drove a 1000 hp Caddy 1000 miles with straight thru exhaust. Still didnt hear a 'drone'. Only unpleasant noise was when it was started cold, I think one of the headers vibrated on the underside somewhere. It went away after it ran 2-3 mins.
Originally posted by rogergarrison: Ive never experienced this drone everyone is talking about in at least 200 cars. My formula is luxury car is quiet, muscle or sports car loud. If this drone is meaning loud, just use bigger or more mufflers. I just drove a 1000 hp Caddy 1000 miles with straight thru exhaust. Still didnt hear a 'drone'. Only unpleasant noise was when it was started cold, I think one of the headers vibrated on the underside somewhere. It went away after it ran 2-3 mins.
Drone is completely different from "loud exhaust". Loud exhaust you hear behind you coming out the tail pipes.
Drone or resonance sounds like the exhaust is attached somewhere and vibrating the floor or passenger cabin inside the car. The exhaust is just matching the frequency range that resonates the cabin - like matching tuning forks... It can be so bad that you don't even hear the exhaust "outside" the car behind you...
With my Indy, exhaust sound shifts from "outside" to a loud drone inside at 2500-3000rpm, then back to "outside" exhaust sound again... The exhaust is not hitting anywhere and sounds OK - but I want to move it "outside" throughout the rpm range.
This is not unique. Google "exhaust drone", and every make of car can get it after changing away from stock exhaust.
Ive never experienced this drone everyone is talking about in at least 200 cars.
Drone is when you get an obnoxious base note resonating in the car when the the vehicle is cruising around certain rpm ranges. Some people get used to it, some people are driven nuts by it.
I can't stand it, I had a flowmaster on my truck when I bought it, the drone was terrible. I figured since it was loud anyway and I didn't like the way the exhaust was done, I thew out the flowmaster for a 12" cherry bomb, I had no idea it would cure the drone problem, I thought drone was just the nature of a louder muffler but I was super happy to lose it.
The worst drone that i ever heard (am automatic T-top Formula with the "muffler eliminator" exhaust that PISA used to sell) would completely plug up your ears, at ~45 MPH. The only thing that I can compare it to, is an old VW bug being driven with the sunroof open and the windows all the way up. It was that bad.
I did a 3800SC swap on my Fiero. II used no mathematical formulas or real science, and just got kinda lucky I guess. Seeing posts from others, and on their recommendations, I wrapped my muffler. Driving on a 200 mile trip after doing the swap, I had no drone at all at speeds from stop to 80MPH.
I did not wrap the whole system, just the down-pipe, and the muffler itself. It is another alternative, and a cheap one to try if you are experiencing drone on your car.
I did a 3800SC swap on my Fiero. II used no mathematical formulas or real science, and just got kinda lucky I guess. Seeing posts from others, and on their recommendations, I wrapped my muffler. Driving on a 200 mile trip after doing the swap, I had no drone at all at speeds from stop to 80MPH.
I did not wrap the whole system, just the down-pipe, and the muffler itself. It is another alternative, and a cheap one to try if you are experiencing drone on your car.
Olejoedad indicated that this worked well for him. The only hesitation that I have is the decreased exhaust system life that can result. I assume that you used an exhaust blanket to wrap the muffler and pipe wrap on the head pipe.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 09-01-2017).]
The only hesitation that I have is the decreased exhaust system life that can result.
I've not had much experience with wrapping exhaust but I would assume painting, curing, wrapping and then painting the wrap would help reduce corrosion but I don't know how that would affect heat transfer and sound dampening.
[This message has been edited by jmbishop (edited 09-01-2017).]
Drone is completely different from "loud exhaust". Loud exhaust you hear behind you coming out the tail pipes.
Drone or resonance sounds like the exhaust is attached somewhere and vibrating the floor or passenger cabin inside the car. The exhaust is just matching the frequency range that resonates the cabin - like matching tuning forks... It can be so bad that you don't even hear the exhaust "outside" the car behind you...
With my Indy, exhaust sound shifts from "outside" to a loud drone inside at 2500-3000rpm, then back to "outside" exhaust sound again... The exhaust is not hitting anywhere and sounds OK - but I want to move it "outside" throughout the rpm range.
This is not unique. Google "exhaust drone", and every make of car can get it after changing away from stock exhaust.
I had a similar problem with my Miata when it had a Magnaflow muffler on it. The best way I can describe how it felt was there was a sound wave that would move from below your ear (from idle to about 2700rpm) then move to the middle of your ear (around 3100 to 3600rpm) and it would leave you with a massive headache if you left the rpm sitting there. And you could feel the sound move above your ear at any rpm above that. Other than that it was just loud; NVH notwithstanding. I think it's needless to say that I ripped that muffler out and replaced it with an OEM one as fast as I could
Your description of the sound moving from the "outside" to "droning" then back to the "outside" is a pretty good description though, I can hear it in my head now that I think about it
------------------ My first car love and dream car: the Fiero
