Eliminating Exhaust Drone to quiet exhaust

[mudbilly]

Hi Barnett,

For some reason i didn't see your post. I got a ping about new posts and started from the bottom reading upwards and got excited after the reading the post by stocktrader.

I apologize for not paying attention ::thumb::

Thanks for your information.

 

[73pony]

All I did was install a correct H-Pipe and drone was gone. 351C running long tubes and Turbo Mufflers.

 

[barnett468]

All I did was install a correct H-Pipe and drone was gone. 351C running long tubes and Turbo Mufflers.

xlnt, there ya go . its best to start with the obvious things first.

 

[Qcode351mach]

Doing just the floor and the trunk isn't going to cure soundproof the car. The inner quarter panels-inner wheels houses-outer wheelhouses act like a big drum and amplify everything. You need more than spraying second skin. On my car I made a rear block off panel from the trunk behind the rear seat covered in raam mat, ensolite and foam sheet http://www.raamaudio.com/categories/Mat-and-Foam-Products/

in addition to doing the entire car this way including inside the doors- floors- dash, I then got thin sheets of water proof packing foam and stuffed inside the rear quarters-also used the ensolite on the inside of the rear interior panels. Car is ultra quite !!!

 

[Stocktrader]

Not much room under the car to do the resonator after the muffler so I did mine before it. It will work either way. I had drone around 2100 rpm but the resonator killed all of it from 1900-2400rpm.

Just have the muffler guy bend a 90 with 30" of pipe on one side. Cut off the short end of the pipe as close to the 90 as possible and add a matching hole in the original exhaust pipe. Bend the resonator pipe to match the original so it can mount flush to the original pipe. Cut it to 26" and make an end cap / mount bracket that can be welded to attach both pipes together. Weld it up.

Done.

Now you can hear your stereo.

 

[mudbilly]

Not much room under the car to do the resonator after the muffler so I did mine before it. It will work either way. I had drone around 2100 rpm but the resonator killed all of it from 1900-2400rpm.

Just have the muffler guy bend a 90 with 30" of pipe on one side. Cut off the short end of the pipe as close to the 90 as possible and add a matching hole in the original exhaust pipe. Bend the resonator pipe to match the original so it can mount flush to the original pipe. Cut it to 26" and make an end cap / mount bracket that can be welded to attach both pipes together. Weld it up.

Done.

Would you have a picture you can post ?

I'm really starting to narrow in on that the drone is emanating from the tailpipes. It is "quiet" from the engine to the mufflers, but after that it is booming.

Also, how did you determine the 26" length. That is around the length that people on other forums have used. From what I can tell (some of them are on truck forums, others, new year muscle, none of them have the separate duasl) Do you have the H crossover?

The reason I ask, is the calculation for tube length takes into account the number for spark pulses per revolution. I'm running straight duals currently. Looking into H pipes, but I do not think that a stock one will fit in the stocks location on the vert. If anyone has one on a convertible, I love to be proved wrong.

Now you can hear your stereo.

Yea, that is actually one of the reasons I am doing this.

 

[mudbilly]

Doing just the floor and the trunk isn't going to cure soundproof the car. The inner quarter panels-inner wheels houses-outer wheelhouses act like a big drum and amplify everything. You need more than spraying second skin.

!

Is that aluminum Dynamat ?

From what the second skin guy told me, the stuff I'm rolling on acts the same as Dynamat (and their product) except I can brush it on and get the same/better coverage/performance easier than cutting and sticking and rolling on all of the adhesive backed pieces.

On my car I made a rear block off panel from the trunk behind the rear seat covered in raam mat, ensolite and foam sheet http://www.raamaudio.com/categories/Mat-and-Foam-Products/

Yea, i'm going to be totally enclosing the trunk with with plywood/foam/sound insulation/whatever. The tricky part is going to be figuring out how to work around the area where the top fits when down. Have to make a trough for that, and also where the hydraulics are housed.

 

[mudbilly]

All I did was install a correct H-Pipe and drone was gone. 351C running long tubes and Turbo Mufflers.

xlnt, there ya go . its best to start with the obvious things first.

From what I've been told, a standard H pipe does not fit on a vert, in the correct location. Does anyone here have one ?

 

[barnett468]

Now you can hear your stereo.

Yea, that is actually one of the reasons I am doing this.

In that case you can simply buy a bigger amplifier. rofl

 

[barnett468]

All I did was install a correct H-Pipe and drone was gone. 351C running long tubes and Turbo Mufflers.

xlnt, there ya go . its best to start with the obvious things first.

From what I've been told, a standard H pipe does not fit on a vert, in the correct location. Does anyone here have one ?

i haven't seen a stock 71-73 convertible exhaust in many years so dont remember but i doubt they did not have a cross over.

this is an earlier convert but it gives you an idea how they fit.

they can also run the pipes under the body plate and install a cross over.

.

 

[Stocktrader]

I have old school Sony Mobile ES XES-M3 amps installed and if thats not enough, I've got 6 Eminence Lab15's at home powered by 2 Crown XTI4000 amps. 133db at 26hz.

Trust me, I have the stereo covered for me and the next 3 houses on each side of me.

Hard to get a pic of the exhaust. Car is covered up outside. But it is nothing more than a pipe running along side of a pipe.

 

[sdstang]

Here is a pic of mine. I also have a wider(4inch) alum drive shaft then stock and a 4r70w trans and still was able to get the h-pipe in my vert.

 

[mudbilly]

Thanks everyone for all the pictures and conversations.

I'm going to be working with the muffler shop next week. We are going to be looking at installing the H-pipe. I'm wondering if the frequency will change with the H-Pipe installed. Or if it will quiet things down.

I downloaded a sound analyzer last night and drove the car to work today. The sound is right at 150 Hz, and this appears to be the same frequency that it stays at during the drone. It does jiggle to 172 Hz during the drone.

I did the math and @ 150 Hz it gives a pipe length of 22". @ 172 Hz the length shortens to 19.18". At idle the major frequency is @ 128 Hz which wants a pipe length of 26".

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EDIT: I just found out that the # I used for speed of sound was at 45F, I doubt that my exhaust is at the temperature :chin:.

If I use 200F which seems more likely the lengths turn out to be:

15O Hz = 25.16"

I am going to stick a thermometer in the pipe and see what it really is.

I'll measure again after the H-Pipe install.

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As of today, if I had to pick a length, it would be 22", but I want to see if he will make it variable length for testing. and then weld when done. I'm hoping that it is real forgiving to the length and it deadens a range of sound.

I'm actually hoping to start working on sound deadening the cab this weekend.

Updates will be provided as I learn

thanks again everyone ::thumb::

 

[barnett468]

The H pipe will not quiet it down very much at all . You need an entirely new exhaust system if you want a big reduction in noise.

 

[73pony]

The H pipe will not quiet it down very much at all . You need an entirely new exhaust system if you want a big reduction in noise.

True but if he is looking to get rid of the drone it certainly helped on mine. I like the semi loud (not going to get a ticket but you still know it is a muscle car) sound just didn't like that annoying drone.

 

[mudbilly]

The H pipe will not quiet it down very much at all . You need an entirely new exhaust system if you want a big reduction in noise.

We will soon see. i dropped the car off at shop on the way to work this morning to see if he can install the H-Pipe.

But, I do have a question, what would an entirely new exhaust system consist of to make it REALLY quiet. Does the cam effect what can be done ?

 

[barnett468]

The H pipe will not quiet it down very much at all . You need an entirely new exhaust system if you want a big reduction in noise.

We will soon see. i dropped the car off at shop on the way to work this morning to see if he can install the H-Pipe.

For your own records, you can take a before and after cell phone vdeo like the guy in the video I posted did.

But' date=' I do have a question, what would an entirely new exhaust system consist of to make it REALLY quiet.[/quote']
What I already posted will make it about as quiet as it can be made.

Does the cam effect what can be done ?

Well, the more restrictive a system is, the more power it will kill off . If you have a big cam, you have to do some good tuning to make it run properly with a restrictive system.

 

[mudbilly]

I bought a Db meter and am using a Sound Spectrum phone app to measure loudness and the frequency that is the major contributor to the noise. From what I read, I'm hoping for a 4 Db reduction & elimination of the drone by adding the H-Pipe.

If I get neither, I don't care, because I can just tell everyone that I added the H-Pipe for the additional torque/HP performance.

The H-Pipe will be installed tomorrow. I'll post an update as to what it does or doesn't do as soon as I can take it for a ride

I plan on proceeding with making the Helmholdts resonators, probably next week. The exhaust shop owner is willing to work with me and learn something new.

I still expect to find that there is a dominate frequency that I can silence.

My goal is still less that 70 Db in the cabin after exhaust mods and insulation. Exceptions will be tolerated for stomping on the gas. ::devil::

 

[jpaz]

You have headers on, so that I would think would make your car sound louder too.

 

[mudbilly]

You have headers on, so that I would think would make your car sound louder too.

That is why I was wondering if I could go back to standard or HiPo manifolds and not worry about compromising the engine performance ?