The Dreaded Drone - Impala Tech
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post #1 of 30 (permalink) Old 06-18-2014, 07:56 PM Thread Starter
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The Dreaded Drone

I've been scanning the inter-tube on how and what to minimize drone in aftermarket exhaust systems. And everything is basically 50/50 on equipment. What is debated is the use of headers vs stock; X and H pipes; and tailpipe resonators, even running just long Cherry Bombs.
What are the opinions on a good flowing, deep note; no drone system for a weekender big block vehicle? Thanks for any and all opinions.
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post #2 of 30 (permalink) Old 06-19-2014, 07:48 AM
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Not using a chambered muffler (ie Flowmaster) is the first step. Second is full tail pipes. If you still have some drone, a small resonator will help. Muffler choice will be the big factor though.
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post #3 of 30 (permalink) Old 06-20-2014, 08:37 AM
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Definitely stay away from Flowmaster 40's. My buddy has them in his 400 SBC 63 Impala and the drone & loudness are terrible. I have a 70 454 Chevelle with headers, 3" full exhaust with Flowmaster Delta Flow 50's and it sounds great - no drone.
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post #4 of 30 (permalink) Old 06-20-2014, 10:31 AM
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Stay away from Flowmaster altogether, all chambered mufflers are prone to drone. On my Olds 463cu.in. I had Flowmasters with 3" exhaust and a X pipe it was horrible, I ended up using big case Dynamax super turbo mufflers. It sounds awesome, nice rumble, loud enough when WOT but nice and quiet when cruising and the drone was gone. I am doing similar setup on my Impala with 2.5".
JMO

BTW in recent testing of all the mufflers Flowmaster is one of the most restrictive mufflers on the market. It flows barely better than stock.
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post #5 of 30 (permalink) Old 06-20-2014, 10:48 AM
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Every car on the road uses chambered mufflers. The only difference is in how restrictive they are. I used Flowmasters on my 582 BBC but they where the biggest case I could find with the greatest number of baffles inside the case. They were sold as stock replacement mufflers for a big block pick-up truck with a single exhaust. A such they where large enough inside to flow all of the exhaust gasses out of my 582 when used in a dual exhaust with an X pipe and tail pipes exciting out under the rear bumper.

I used to have a Baldwin-Motion Phase III L-88 427 powered 1968 Camaro that had Corvette side pipes and a Hooker Competition Plus series 2-1/8th inch primary pipes. The engine noise from the four foot long glass-pack exhaust exiting before the rear tire would give me a headache by the time I drove home from work every day. This was probably due to my windows always being down because for some reason It didn't come with A/C.

Drone is generally due to where the exhaust exits the vehicle. An X or H pipe really helps to lower the sound levels and reduce drone. The difference is in the costs. H-pipes are cheaper, but the X pipe will flow a lot better, with lower back pressure in the system. The size of the exhaust pipes is most important.

The bigger the pipe size the noisier it will be. This is why the a diesel truck that has a 350 cube motor has a six inch exhaust pipe pointing straight up. The pipe size is required by the diesel engine that doesn't tolerate any back pressure in the exhaust system. The going straight up is to point the noise away from the public.

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post #6 of 30 (permalink) Old 06-20-2014, 11:21 AM
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I beg to differ, there are 3 most common types of mufflers on the market for street use.

Chambered- exhaust gasses are routed through multiple chambers and around any number of angled, sound-cancelling plates, known as “baffles”.

Turbo mufflers - exhaust flows in an S-shaped pattern through perforated tubes, usually 3 or fewer on performance mufflers, so exhaust flow changes direction less. This means engine exhaust leaves the muffler faster, for an increase in horsepower and a better exhaust tone. also, turbo mufflers occasionally use additional fiberglass packing around the tubes for additional sound control.

Glasspack - the simplest style of muffler used on performance rides. At the heart of a glass pack muffler, is a single, perforated exhaust tube. This runs from inlet to outlet, with quieter mufflers using an angled tube and louder mufflers using a straight tube. Fiberglass or steel wool packing is wound around the tube
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post #7 of 30 (permalink) Old 06-20-2014, 10:23 PM Thread Starter
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The reason for opinions is because I just installed a Comp Cams 268H specs out at 219* at 485 lift with 110 l/s. This is an awesome sounding and performing cam in my stock 402 BBC. 100% better than my 216* 515 lift that I had in it, very unexpectedly surprised!
I'm wanting to accent that cam hit. I would post a clip but exhaust is tinny and sounds like your hitting the side of an empty coffee can----the metal ones LOL --- and does the cam no justice. Exhaust exits behind the rear wheels at 2.5" from stock manifolds, back.
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post #8 of 30 (permalink) Old 06-21-2014, 12:20 PM
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You need some headers, stock manifolds are choking it right at the engine, so no matter what you put behind it it's not gonna sound the way you want. What mufflers are you running now?
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post #9 of 30 (permalink) Old 06-21-2014, 01:18 PM
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When it comes to sound you can follow this guys lead.



If you seek to make noise use a bigger pipe, and leave the muffler off.

As you think that running a big cam on the street is the way to go then follow this guys lead:



You can buy a cam to improve performance or impress your friends, but generally not both. I used to drive a class legal B/MP and an A/G NHRA car on the street as a my daily driver. I was younger then and didn't mind getting two to three miles to the gallon back when gas cost only a third of your minimum wage salary instead of the half of your minimum wage salary as it costs today.



As I said earlier, when I was younger, I had glass packs on my cars because the car mags said it made more power. Then as I aged I used Chevrolet's Corvette chambered exhaust (but discovered that they are just longer glass packs). I quickly switched over to a set of Chevrolet (it was made by Walker, and still is today) Corvair's turbo charged mufflers with turn downs exiting before the rear wheel. The turbo charger mufflers where much quitter and mellower than the glass packs. They also lasted a lot longer because I was no longer collecting as many tickets for being too loud when driving through the big city.

Your desired level of noise and how rough an idle you desire is an expression of your taste in a car not necessarily shared by your neighbor.

I mention that because before I moved out into the country thirty years ago, I lived in the suburbs of the big city. My neighbors often expressed their discontent with my driving home at 2 AM with a big block running glass packs. My father, who finally asked me to move out when I drug home my 14th project car, stated he could hear me coming from four miles away. Back then before the suburbs morphed into a city it was much quieter.

Big Dave

Last edited by Big Dave; 06-21-2014 at 02:21 PM.
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post #10 of 30 (permalink) Old 06-21-2014, 03:25 PM Thread Starter
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@ Eddie...Thrush welded at 13" on the case. I got them just to have some sort of exhaust instead of straight pipe. I thought of header's but considering heat and operating range of engine, I will not see any benefit, just higher underhood temps.
@ Dave...it's no where near say a thumper cam but with my cam's spec's at 650 rpm's on a 4 speed it does count them off.
I did notice today that passenger side is more tame than the drivers side which has a more undesirable note. System is sealed from down pipes to tails. ??? Bad muffler internally?
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post #11 of 30 (permalink) Old 06-21-2014, 03:56 PM
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If you don't there any benefit in headers, you are misinformed. By installing headers it would allow engine and that cam to breathe and it would lower the under hood temperature as individual steel tubes will dissipate heat much better than cast iron. Headers are probably best bolt on improvement you can do, cause stock manifolds are extremely restrictive. Even a stock engine will see a HP improvement. The scavenging effect of a properly designed header can be a positive benefit to the induction system and to power output as a whole. I Personally I would never run painted or raw headers, ceramic coating is the way to go. On your engine I wouldn't run anything bigger than 1 3/4 primary tubes.

I think modern design cams are way better and a big improvement over the stock and I don't see your cam as aggressive for that engine. However cam is a crucial part of the whole system. If you mismatch it with the rest of the components such as rear end gears for example, it will make your car run like crap. If you are looking for that lumpy rough idle, this cam will not do it, but you really can't go any bigger on otherwise stock engine.

Thrush welded muffler is chambered and sound just like Flowmaster. If it was my car I would do headers and Dynamax super turbo, keep it at 2.5". I think Dynamax the best sounding muffler on the market. Pypes also sounds really nice, but everybody has their preference.
JMO.

Last edited by 67SS; 06-21-2014 at 04:12 PM.
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post #12 of 30 (permalink) Old 06-21-2014, 04:12 PM Thread Starter
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Your thought's on the Hushpower series? I'm not leaning to F.M, heck if I can get stock Walker's and resonators to get the sound I will but I'm just trying to get all the info. as possible and to help anyone else that stumbles on this post.
As to header's, I understand that its a right combo of part's but would stock manifolds cause the tinny note? I do have 2.5" throughout. I will eventually go with coated header's but at close to $200 for the coating it'll have to wait.
On the cam... Comp did a great job on this recomendation... +1 for them
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post #13 of 30 (permalink) Old 06-21-2014, 04:16 PM
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I think headers and better mufflers is what you need to achieve the sound your are looking for. If you are choking it right at the source, than it don't matter if you got 2.5" throughout.
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post #14 of 30 (permalink) Old 06-21-2014, 04:40 PM Thread Starter
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True that! so what your saying is the undesirable note is from stock manifolds.
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post #15 of 30 (permalink) Old 06-21-2014, 07:02 PM
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Stock manifolds and chambered muffler.
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post #16 of 30 (permalink) Old 06-21-2014, 10:20 PM
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Because exhaust gas removal is so important in virtually all thermodynamic heat cycles from Otto, Diesel to Stirling, Rankine, or Brayton, I was required to read three different text books on the design and function of an exhaust system and the valves that control it.

One of the texts addressed exhaust gasses as a fluid dynamics problem (with mathematical modeling that provided lots of home work problems and test questions). Another talked about the harmonics of tuning an exhaust just as you would a steam powered organ, though it isn't really relevant to modern cars it does become very important not to mention destructive when the flow approaches super sonic speeds which changes with the pressure or temp since they are reciprocals of each other.

The final book combined the two for some really complex higher order math test questions, but also provided insight into what is actually happening once the valve is opened.

If you are concerned about ram tuning and scavenging of the exhaust system, you can forget that concept all together if you are running mufflers. Fluid dynamic requires the pipe to be open to the atmosphere to support a standing wave The harmonic pulse that causes the gas in the pipe to be compressed or be expanded (reducing the pressure) has to be reflected back up the pipe for that to work and that requires the pressure in the pipe to instantaneously drop to a gauge reading of zero or to be open to atmosphere. That is why race cars run uncapped, not because they just want to make noise.

Pressure pulses do have another affect upon the exhaust of a multicylinder motor. At some point in the firing order of a balanced engine (one with four cylinders or a multiple of four cylinders) there will be two cylinders adjacent to one another that open sequentially. Because one valve is opening next to one that has already vented; the valve on a long duration cam (this is where the Thumper or VooDoo or what ever brand name they come up with to call a cam that has most of the duration on the exhaust side of the cam centerline) is still off the seat when a high pressure pulse expands into the exhaust manifold. This surge of high pressure gas enters through the open valve that is closing and contaminates the cylinder with exhaust gas that won't burn (which is what the EGR valve does). It not only fills the chamber with spent gasses it kills any hope of developing a strong vacuum signal to draw in fuel from the carb or air from the intake manifold. This creates a weak or nearly dead cylinder depending upon how long the exhaust duration is.

The exhaust having a long duration to get the rumpitty-rump sound is more beneficial to the engine than having long duration on the intake side of the cam. Only one cylinder in an eight cylinder motor is affected (two on a V-12 or three on a V-16). This beats the pants off adversely affecting the performance of all eight by having a long duration on the intake side.

Headers can fix this contamination and give you back your cylinder's power. This is the bump in horsepower obtained by any header that has a tube length of nine inches or more. That 18 inch length from the cylinder to the collector and back up to the adjacent cylinder will cover a motor's flow up to 8,000 RPM. At higher speeds you will need a longer primary pipe. I would also point out that tuned headers are tuned for one specific RPM, making the concept next to useless for a drag car, but offers free horsepower to a car that is taking a leisurely 400 to 500 mile drive on Sunday on a high bank oval track.

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post #17 of 30 (permalink) Old 06-22-2014, 08:36 AM Thread Starter
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Understood Dave, believe it or not . Thanks.
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post #18 of 30 (permalink) Old 06-23-2014, 08:33 AM
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This thread is confusing. Are you looking to make sure you don't have drone or are you trying to get rid of the tinny sound?
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post #19 of 30 (permalink) Old 06-23-2014, 09:23 AM
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He wishes to get rid of the higher frequencies (that will required a tuned baffled system to cancel out the higher frequencies selectively, or a material that absorbs the higher frequencies only), that makes the exhausts sound tinny. Additionally he wishes to prevent droning which is a problem when the car cabin becomes a resonance chamber reinforcing (rather than canceling out) the harmonics in the exhaust sound.

There are materials that can be selected to absorb a specified acoustical signal (sound frequency, but you have to select a material that is also immune to high heat, moisture and the acids found in the exhaust pipe. This limits the material list and if you include cost that is not going to result in an economical solution.

Acoustics has advanced to the point where we can engineer a simple baffled muffle that will cancel any specified frequency. All you have to do is set up a steel walls to reflect the sound back at the source a specified distance from the source. The distances varies with the frequency you wish to cancel.

Since sound has a near infinite number of frequencies (though not all are generated in a car's exhaust), you will need a bunch of reflecting surfaces to reflect the sound back at the source. An alternative is to set your reflecting surface at an angle to reflect it at another angled surface and let the bouncing sound waves cancel each other as they are reflected and absorbed dissipating their acoustical energy. The more room inside the echo chamber and the more reflecting walls the quieter the end result will be.

Stock exhaust systems use both systems to dump the expanding and cooling exhaust into two to four chambers that vary in size connected by perforated pipe that has different sized holes in the pipe to allow the various frequencies to be absorbed and canceled out by echoing in the different sized chambers.

This what a Flowmaster 40 series looks like inside:



Here is what a Flomaster 70 series looks like inside. The 70 series is a longer and wider muffler than the smaller 40 series so it is harder to find room for it under a smaller car:



Though a Magnaflow looks like a baffled exhaust on the outside (due to it's oval shaped case) it is basically a glass pack that is generally round in shape:



The inside of a typical Thrush glass pack:



A close up inside a conventional muffler showing how the gas gets out of the pipe to cool and expand absorbing energy:



A diagram showing the interior of the of a Walker muffler:



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post #20 of 30 (permalink) Old 06-23-2014, 09:47 AM Thread Starter
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As was stated in my first post, I'm trying to get opinion's on targeting exhaust note and resonance, price to achieve this will be understandably higher than the norm. I just want to limit the under car time . ?????? 3 chambered F.M and resonator's ????? Thanks for all the responses!
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post #21 of 30 (permalink) Old 06-23-2014, 03:46 PM Thread Starter
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Referring back to my post on 6/21 about the exhaust note is more undesirable, I just thought could that be from the 5 and 7 firing sequentially? I'm sure long tube's would cure that?
I have noticed the Ford 426 and the Crys 440 don't have that pop on the left cylinder bank. Maybe it's just not that noticeable.
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post #22 of 30 (permalink) Old 06-23-2014, 04:37 PM
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I am not sure I am following here.
Firing order is the same as on many, many other and not all sound like that.
What exactly are you trying to get??
To me it looks like you want a more agressive/lumpy sound from your cam.
If that's the case you need a bigger cam.
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post #23 of 30 (permalink) Old 06-23-2014, 06:31 PM Thread Starter
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@ Eddie I get that a lot. Ok let me try again . Exhaust system only on a basically stock 71' 402 with a Comp Cams 268H.
First situation: Looking to get just a deep tone at idle and the same at cruise. No crackle when revving or letting out of it like Cherry Bombs do.
Second: There is a distinctive exhaust pop from the drivers side tail, I even uncorked the muffler earlier today and still noticed it......not like wiped cam but more like a dead cylinder but doesn't seem out of the norm as far as firing . New plugs installed when cam went in and new Taylor wires, HEI checks out. I was asking if this is normal sound for GM V8's because because of the 5/7 order. I don't notice it on other V8's.
I guess I need to try to get a audio clip in here to really hear whats going on.
Sorry to be so confusing.
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post #24 of 30 (permalink) Old 06-23-2014, 06:52 PM
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Quote:
Originally Posted by 68imp View Post
?????? 3 chambered F.M and resonator's ?????
In the very first day several responses said to stay away from Flowmasters if you don't want drone. They will also accentuate the tin sound of a performance cam.

If you are running a heat riser valve the passenger side will be quieter. Video your car and post it along with some videos you do like the sound.
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post #25 of 30 (permalink) Old 06-24-2014, 12:16 AM Thread Starter
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Will do. Thanks all.
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