Eliminating Exhaust Drone to quiet exhaust

[mudbilly]

Hi All, I know this conversation has probably been talked about before, but I'm not finding a good thread so I'm looking for advice and opinions.

I really want to quiet down my exhaust. I don't think that what I have can be modified to give me what I want (although, I'm still having a debate with myself as to exactly what I do want )

I have terrible drone at certain RPM and the exhaust is just too loud in general. This is strictly a case of hearing damage avoidance and not what I like to hear. I've had this loud exhaust for 10 years, but only lately have been wanting to tone it down.

The local exhaust shops say that there is not much a muffler swap can do to quiet this down, so I'm wondering where loudness is coming from?

I have a mild cam a 600 cfm Edelbrock and with 335 HP. It has shorty headers and straight pipes, no H or X. I'm not concerned about power loss or gain as long as it doesn't hurt the engine.

Does the cam make the engine more susceptible to the drone and loudness or is it the headers?

Would running stock manifolds eliminate this issue?

Part of me wouldn't even mind it being as quiet as stock motor, but is this feasible with the build?

 

[TommyK]

I don't think camshaft selection plays much of a roll in exhaust drone issues. Mufflers however, can make a big difference with drone.

I was running Flowmaster 40's and the drone was horrible. I switched to Dynomax super turbos and 90% of it was eliminated.

A cross over pipe will help as well. I don't think it matters whether it's a X or H pipe.

Also, make sure your exhaust isn't touching the chassis anywhere and use rubber mounts to hang it.

Installing sound deadening material, especially in the trunk can help as well.

I am assuming you have tailpipes. If not, that would be the first thing to address.

 

[Stanglover]

Hi All, I know this conversation has probably been talked about before, but I'm not finding a good thread so I'm looking for advice and opinions.

I really want to quiet down my exhaust. I don't think that what I have can be modified to give me what I want (although, I'm still having a debate with myself as to exactly what I do want )

I have terrible drone at certain RPM and the exhaust is just too loud in general. This is strictly a case of hearing damage avoidance and not what I like to hear. I've had this loud exhaust for 10 years, but only lately have been wanting to tone it down.

The local exhaust shops say that there is not much a muffler swap can do to quiet this down, so I'm wondering where loudness is coming from?

I have a mild cam a 600 cfm Edelbrock and with 335 HP. It has shorty headers and straight pipes, no H or X. I'm not concerned about power loss or gain as long as it doesn't hurt the engine.

Does the cam make the engine more susceptible to the drone and loudness or is it the headers?

Would running stock manifolds eliminate this issue?

Part of me wouldn't even mind it being as quiet as stock motor, but is this feasible with the build?

Have you considered that the drone might not be exhaust but resonance through the body? I say this because all the 4, 71-72 Mustang I have owned, suffered from a drone or resonance which drove me to sleep, literally, even in the daytime and in short order. This might sound weird, but after I insulated the sh*t out of the interior, no more drone and I wasn't feeling like I needed a snooze.

If it is your exhaust and your shop can't help, neither can I!! LOL

Good luck with it. Funny thing is most of us want a throaty exhaust and that's one thing, but I do understand where you're coming from, we only get one pair of ears!

Geoff.

 

[Don C]

+1 on the Dynomax super turbos, I've had good luck with them. I also agree with the cross over and the sound defender. One other thing to check is to make sure the hangers are in good shape and none of the exhaust is touching anything, including emergency brake and speedometer cables. Straight exhaust tips might help, rather than turn downs. I've also used resonator tips with some success.

 

[luxstang]

Here's what I witnessed with my car:

Years ago I've had long tube headers installed with straight pipes (2 1/4 inch) and Edelbrock mufflers.

Waaayyy to loud. So we simply swapped the pipes and put 2 inch pipes in, keeping the headers and mufflers. The result: great sound and no drone frequencies whatsoever.

After I lowered the car and the long tube headers scraped the road I decided to get rid of that crappy backyard type exhaust and ordered a repro exhaust for our cars that looks factory. I wanted original manifolds but I couldn't find any, so I went with shorty headers.

The pipes are 2 1/4 inch again, the mufflers are still the same Edelbrocks and again drone frequencies are back. And they are unbearable.

So it was only an issue of the diameter of the pipes on my car.

Friends of mine has similar issues and they simply installed stock manifolds instead of headers, keeping all the rest as it was and the problem was solved. (Plus they witnessed an increase in torque).

So I'd say if you have access to stock manifolds that might be your solution. Or smaller diameter on the pipes but that means swapping the entire exhaust.

 

[barnett468]

need more info on your system including muffler type.

to reduce drone, you can install resonators or try the magnaflow mufflers . the magnaflows are stuffed full of steel wool an fiberglass and are straight thru and noisy out the rear but quieter than others inside the car.

the quietest mufflers would be baffled glass filled ones like stockers . walker makes several and the bigger the better.

 

[MotoArts]

https://en.wikipedia.org/wiki/Helmholtz_resonance

and

http://truestreetcars.com/forums/general-automotive/25747-all-you-mustang-guys-exhaust-drone.html

At one time I had seen undercar pictures of resonator tubes someone had built on their Fox Mustang but can't find it. They were basically were attached to one tube per side of the H pipe, built to the dimensions using the formula above.

V8's by nature generate that 2000rpm drone due to the firing pulses of the 90 degree vee. I'm not that much into the cause or engineering of the drone, but I know it was horrible with the stock 4 cat H pipe and particular chambered garbage cans I tried on my car (that lasted exactly 2 days till I found someone to buy them).

Dynomax Super Turbos fixed the dilemma quickly and easily.

 

[barnett468]

dnomax super turbos are far louder than magnaflows.

 

[mudbilly]

I'm thinking it is the headers. The worst part about that is that I threw away a perfectly good set of stock manifolds 10 years ago when I rebuilt the original engine........:atomic:

The parking brake cable is definitely pulled hard against the exhaust. That has been on my to fix list for a while, because it really interferes with trying to use the brake, but I didn't think about it causing noise issues. I'm going to just disable that, I never use it the way it is now anyway. While under there I'll look to see where else the exhaust may be touching frame members and also look to see how it is hung.

The muffler shops, even the "performance" ones, don't see anything wrong with the system, loud is good to them. I have an appointment Tuesday to have resonators installed, but am cancelling that because I think that they are just throwing parts at the car without knowing if this will actually fix anything. The other shop says that the mufflers I have are the quietest there are and that every brand is going to act pretty much the same in respect to the drone.

I'm doing some research on Corsa and will call them tomorrow. There website doesn't list anything for older cars.

That being said, and as a couple here have mentioned, everyone has had varying success with different mufflers, but a brand/type that is successful for one person, does not work for the other. I've cruised a lot of different forums, from classic cars to new rides and a common core is that for everyone that had success with a certain muffler, there is someone else that it made it worse.

It is almost like you have to have a acoustic engineer specials tune the exhaust for your particular situation.

It appears that the drone is really coming from behind me while driving. This might be misleading, but I' thinking that the trunk is acting like a big boom box.

I don't mind the noise if it stays outside of the cabin, so the plan for now is to sound proof the heck out of the trunk and rear floor.

I have 5 gallons of Second Skin Spectrum vibration coating on order and hope to get it brushed in over the holiday weekend, weather and other functions permitting.

Next will be to enclose the trunk with plywood/carpet ( I really like what someone on this site did. I bookmarked the link) and Second Skin Luxury line that. I'm going see how well I can box in the area where the top sits when it's down since this is a direct air path from the trunk to the cabin.

Then I'll see how far I need to go with the actual exhaust.

I have a Db meter and currently I'm getting:

105 Db in the trunk

95 Db in the cabin during drone

85 in the cabin when engine at non-drone RPM

I want 70Db in the cabin at all times. i don't think that I can get there with just the sound deadening/blocking.

That is why I'm thinking to just go back to original exhaust. They had to be quiet, and if it doesn't hurt the engine with the cam any, I am sold.

 

[mudbilly]

I say this because all the 4, 71-72 Mustang I have owned, suffered from a drone or resonance which drove me to sleep, literally, even in the daytime and in short order.

I would love it if the drone put me to sleep, unfortunately, it is more the sound of a jet airliner at 100 ft coming in for a landing.

 

[mudbilly]

OK, So now I'm looking at stock exhaust manifolds (Repros). What is the real difference between "standard" and "HiPo" ?

 

[Stanglover]

I say this because all the 4, 71-72 Mustang I have owned, suffered from a drone or resonance which drove me to sleep, literally, even in the daytime and in short order.

I would love it if the drone put me to sleep, unfortunately, it is more the sound of a jet airliner at 100 ft coming in for a landing.

Yeah, but falling asleep at 80mph and not waking up till I hit the gravel shoulder was NOT to be loved. I saved the car from the ditch and carried on. That's was when I insulated all the cabin areas I could get to.

I think that all you need to insulate is the interior of the cabin. You are right when you say the sounds seems behind you. Insulate behind the rear seat and under it and the wheel arches and the parcel shelf area. A good underfloor sound mat as well. Obviously, getting a better exhaust as well, everything helps as these cars are definitely Boom Boxes on wheels.

My current car runs the original manifolds and is quite a bit quieter than my 72 with headers. These are on 351C's though.

Been an interesting read here,

thanks,

Geoff.

 

[sdstang]

I did the dynamat super turbos too. I have hooker headers also. Very nice option. At first now h-pipe and it was loud and chatty sounding. Then we cut one in and way better. The other thing we did was go from 2.5 before the Mufflers to 2.25 after. This helps with drone. I have a vert so this was important to me. Here's a clip.

http://s172.photobucket.com/user/jharness/library/Mobile%20Uploads?sort=3&page=1

 

[barnett468]

OK, So now I'm looking at stock exhaust manifolds (Repros). What is the real difference between "standard" and "HiPo" ?

Headers do not cause a drone.

The hi po manifolds are much freer flowing and they are reproduced and are nearly as quiet as stock non hi po ones.

Using Magnaflows and resonators will reduce drone.

I saw you do not have an H pipe so your pipes are single . This will definitely promote drone, so you can reduce it by adding one of these also.

Another option is to run a pipe off of each pipe that is capped on the end and around 20" long . These are called "side branch resonators" and some production vehicles have them . Different lengths of these pipes affect drone at different rpms so you might have to try different lengths until you reduce it as much as is possible . The longer they are, the lower the rpm they will affect . One way to do this is to put a stub pipe off each main pipe that is nearly the same size and around 3" long, then make two pipes around 18" long with the ends capped off with a 1 1/2" long slit in the ends that will slip over this pipe and clamp on . If it still drones, make longer pipes like 24" and try those . These should be installed after the mufflers.

Here is a video with and without these extension pipes

https://www.youtube.com/watch?v=ijwxKDVnAec

.

 

[Don C]

Has anyone tried the Dynomax VT? They're supposed to eliminate the drone, but still provide some sound when the throttle is opened.

They're on my wish list...

 

[barnett468]

Has anyone tried the Dynomax VT? They're supposed to eliminate the drone, but still provide some sound when the throttle is opened.

They're on my wish list...

Depending on your setup the valve may clank and rattle at idle and the spring inside them has broken in less than a year on many of them.

 

[Stocktrader]

Depends on your drivetrain combo if you get drone or not. My convertible had no drone. The fastback had bad drone.

I did the helmholdts resonator with a 26" capped off empty pipe added to both sides of my exhaust and now there is no drone at all. It sounds perfect in and out of the car. The exhaust shop guy was in his 70's and never saw it done so I had to tell him what to do. I think he thought I was nuts.

All the manufacturers now tune their performance cars for the exhaust note and you will find similar lengths of pipe or a box that looks like a muffler but is really just a different flavor of the helmholdts resonator.

 

[mudbilly]

Depends on your drivetrain combo if you get drone or not. My convertible had no drone. The fastback had bad drone.

I did the helmholdts resonator with a 26" capped off empty pipe added to both sides of my exhaust and now there is no drone at all. It sounds perfect in and out of the car. The exhaust shop guy was in his 70's and never saw it done so I had to tell him what to do. I think he thought I was nuts.

All the manufacturers now tune their performance cars for the exhaust note and you will find similar lengths of pipe or a box that looks like a muffler but is really just a different flavor of the helmholdts resonator.

Perfect timing, I just stumbled upon the Helmholdts while researching this and am going to have some fabricated and installed by the local exhaust shop (although he does not know this yet )

Did you put yours after the muffler? I crawled under the car last night and it looks like a perfect place right behind the axle between the axle and gas tank.

Do you remember what RPM you had the issue at? I am in the process of calculating the length and would use your measurement as a sanity check before having them made. I was actually thinking of having them make a sliding fit prototype for experimenting so that they could be length adjusted for fine tuning before they are actually welded.

Do you have the equation that you used ? I have a couple from a couple difference sources but haven't had a chance to compare them yet to see if they are basically the same.

 

[barnett468]

Depends on your drivetrain combo if you get drone or not. My convertible had no drone. The fastback had bad drone.

I did the helmholdts resonator with a 26" capped off empty pipe added to both sides of my exhaust and now there is no drone at all. It sounds perfect in and out of the car. The exhaust shop guy was in his 70's and never saw it done so I had to tell him what to do. I think he thought I was nuts.

All the manufacturers now tune their performance cars for the exhaust note and you will find similar lengths of pipe or a box that looks like a muffler but is really just a different flavor of the helmholdts resonator.

Perfect timing, I just stumbled upon the Helmholdts while researching this and am going to have some fabricated and installed by the local exhaust shop (although he does not know this yet )

Did you put yours after the muffler? I crawled under the car last night and it looks like a perfect place right behind the axle between the axle and gas tank.

Do you remember what RPM you had the issue at? I am in the process of calculating the length and would use your measurement as a sanity check before having them made. I was actually thinking of having them make a sliding fit prototype for experimenting so that they could be length adjusted for fine tuning before they are actually welded.

Do you have the equation that you used ? I have a couple from a couple difference sources but haven't had a chance to compare them yet to see if they are basically the same.

.

The "Helmholtz Resonator" is also called the side branch resonator or in line resonator which is what I posted the info about twice and a video, and they mount AFTER the muffler.

These should be installed after the mufflers.

They are also original equipment on some of the older Mustangs as early as 1965 as shown below . Some people mount them before the muffler, however, I don't know how effective that is, and again, as the video I posted shows, they do not reduce the exhaust noise by a great deal, and again, the lack of a cross over tube greatly increases the chance of having drone, which means that even with the resonators, you may still have some drone.

Even if you use a formulae, you may still have to try different lengths, therefore, if you don't make them adjustable as I suggested, you may find yourself spending a lot of time and money at the exhaust shop.

This s a stock system from a 271 hi po car and it has a cross over tube, two fiberglass filled AND chambered mufflers, and two resonators.