Eliminating Fastback Coupe Cabin Drone? - Pontiac Solstice Forum
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post #1 of 20 (permalink) Old 09-17-2018, 09:43 PM Thread Starter
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Eliminating Fastback Coupe Cabin Drone?

I asked RickVB about his exhaust system in another thread, and thought it best to start a new thread.

To bring everyone up to speed RickVB has a fastback coupe and a performance exhaust plus a HFC, and I inquired about how it sounded upon initial startup and after the exhaust warmed up. Below are his comments. Also, I have a Solo Mach Shorty exhaust on our GXP coupe, and also bought a HFC a couple years ago that's been sitting on the shelf in the garage. I will eventually install it on the coupe even if I have to deal with cabin drone, but if there's a way to eliminate it I'd like to hear any ideas.


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Originally Posted by RickVB View Post
Chop, the sound is quite loud for the first 30 seconds after a cold startup both inside and outside the vehicle, then settles down to an annoying drone inside. The sound level is worse at certain engine output levels, and I wish I could reduce it. However, I'm unwilling to reduce the engine performance to reduce the sound problem, so I've let it go. I've kind of gotten used to it over the years, so by inertia I haven't done anything about it.

I'd like to discuss this further, but I guess we should find the correct thread to do so first.

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Mr & Mrs ChopTop's 09 Fastback & 06 Vert Mods thread:https://www.solsticeforum.com/forum/f...session-75468/ Original join date; Oct 2005 under LowLife handle.
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post #2 of 20 (permalink) Old 09-17-2018, 09:43 PM Thread Starter
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Greybeard also posted something I've never heard of before:
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Originally Posted by greybeard View Post
For drone you been to build a Helmholtz resonator. Use the on my card. Search exhaust drone there are sites that tell you how to make. They even use system in skyscrapers ventalation systems. High end cat back systems have them built in.
Below is a picture of an exhaust with a Helmholtz resonator attached to prevent drone. A Helmholtz resonance or wind throb is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle.

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Mr & Mrs ChopTop's 09 Fastback & 06 Vert Mods thread:https://www.solsticeforum.com/forum/f...session-75468/ Original join date; Oct 2005 under LowLife handle.

Last edited by ChopTop; 09-17-2018 at 09:46 PM.
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post #3 of 20 (permalink) Old 09-17-2018, 10:11 PM
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A little off topic, but when I saw "drone" I thought of a pesky drone flying around the cabin area.... How cool would that be? Sign of the times...
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post #4 of 20 (permalink) Old 09-17-2018, 10:48 PM
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2.4 coupe.... not sure if or how it might apply to a GXP

a lonnnnggg time ago we had a discussion about coupe drone and we never came to a conclusion.. someone was going to run a borescope down to the oem pipe fat spot to see what was in it. can't remember the results, maybe nothing was in it....

the original coupe exhaust has a 'fat spot' (pic 1) in the pipe that we thought/think might have be some kind of resonator/attenuator; I don't think the same 'fat spot' is in a convertible exhaust.

I tried a moroso resonator (pic 2) (an end view of the internals was posted (I think I did…) in the previous thread, it has a spiral swirl flow path) of sorts to see if it would alleviate the drone, but no luck
Bill
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Last edited by wmf246; 09-18-2018 at 04:00 AM.
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post #5 of 20 (permalink) Old 09-18-2018, 07:33 AM
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Ping @wspohn (here or on Kappaperformance). He went through several iterations to get rid of the drone on his coupe.

Owner of "Campbelle", a Brazen 2008 GXP ... with mods piling up...
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post #6 of 20 (permalink) Old 09-18-2018, 08:04 AM Thread Starter
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I know this sounds crazy, but I've seen people wrap their exhaust headers, and it made me wonder if wrapping the entire underbody exhaust pipes (between the HFC to muffler) would make a difference as far as cabin drone? I'm thinking that exhaust wrap would also work like sound insulation?

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post #7 of 20 (permalink) Old 09-18-2018, 10:16 AM
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Trying to isolate the exhaust from the car with wraps might get you a little, but I doubt it would solve the problem. I went to a Solo Mach system. It works and has minimal (though not zero) drone using the HFC.

I also contributed two more data points along the way - street/race = no way, street/race with added in line mufflers = no way. After that I didn't want to risk buying yet another system that I'd have to replace so at Jeff's (SOLO) suggestion went with their Mach system which is fine. If anyone else has used a Mach Shorty on a coupe we can complete the data.

I have one related question. I never remove my roof panel. Maybe those that do, and have a Solo system, can advise whether the drone changes or goes away when the roof is off. Just curious.

PS - those who bitch about Solo prices should count their blessings. They are an absolutely top notch system and while the whole Mach system costs $800, the rear cans alone cost over $1,000 for my BMW.
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Last edited by wspohn; 09-18-2018 at 10:18 AM.
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post #8 of 20 (permalink) Old 09-19-2018, 05:10 AM Thread Starter
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Anyone ever think about using Dynomat in the rear hatch area? BTW, is it the loudness of a performance exhaust and a HFC, or is it the resonance (sound waves) of the exhaust and HFC that is infiltrating the hatch area (or a combination of both)?

https://www.amazon.com/GTMAT-Automot.../dp/B00BBFT3LA
Product description: GTMAT ONYX 24 sqft Automotive Sound Deadener Resonance Dampener Real True Butyl - Noise Deadener Installation Kit Includes: 24 x 1sqft Sheet (12” x 12”), Degreaser, Application Roller, GT MAT Decals, Instruction Sheet $89.99

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post #9 of 20 (permalink) Old 09-19-2018, 07:01 AM
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personally, "I" think it is a tonal/frequency harmonic of the 'sound' of the new exhaust system; BUT I thought my new inline moroso resonator/muffler would eliminate that...

whatever it is, GM's OEM exhaust does not have that problem
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post #10 of 20 (permalink) Old 09-19-2018, 07:07 AM
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I have the Mach solo, center exhaust, on my coupe. I do not have a hfc. I hear no drone in my car. I haven't had the hard top on in three years and don't expect to ever install it again. The soft top has been off all summer but will put soft top on when we head to mkc West Virginia week long event, next month. Love my solo Mach exhausts that I have on both my Solstices.

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post #11 of 20 (permalink) Old 09-19-2018, 08:15 AM
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Not a coupe owner but a couple of points I'd like to make here : The wrap that Chop mentions is primarily for heat reduction and as far as I know does nothing for sound .As a side note many header manufactures will not honor warranties to people who use this stuff because if not properly applied will trap moisture ,when I purchased headers for the Chevelle this was clearly stated in the instructions . As for the Dyna mat again when I redid the Chevelle interior this past winter I did the floors with Eastwoods version and did notice a difference as far as sound and especially heat transfer in the car . It's a built big block with a 3 inch exhaust from the headers back and Flowmaster 40 mufflers so there is no need for a radio !
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post #12 of 20 (permalink) Old 09-19-2018, 12:40 PM Thread Starter
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The main reason I'm asking about drone is because I picked up a Solo HFC around three years ago (already had GMPP). But it's been sitting in the garage on a shelf since then. I don't have a good reason for not installing it other than we haven't been driving the coupe that much. About the only thing I do is take it on an 18 mile circuit every few weeks during the driving season.

The Solo Mach exhaust is somewhat loud upon initial start up, but that is partially due to it being in the garage. Once it's warmed up it quiets down, and while I can hear it while driving around, it's not so loud that it bothers me. Then again, I'm not in the car that long, maybe 30 minutes at a time.

Having said that I've always planned on installing it because it cost too much to just let it sit on the shelf, and it would be great to have a few extra ponies. But the coupe cabin drone issue is always at the back of my mind, and I don't remember reading that it's every been resolved for fastback owners.

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post #13 of 20 (permalink) Old 09-19-2018, 12:45 PM
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Stick the HFC in and we'll have a complete data set with my car and yours. Only way to tell is try it and see. The Mach is just fine with it.
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post #14 of 20 (permalink) Old 09-19-2018, 03:32 PM
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Quote:
Originally Posted by ChopTop View Post
The main reason I'm asking about drone is because I picked up a Solo HFC around three years ago (already had GMPP). But it's been sitting in the garage on a shelf since then. I don't have a good reason for not installing it other than we haven't been driving the coupe that much. About the only thing I do is take it on an 18 mile circuit every few weeks during the driving season.

The Solo Mach exhaust is somewhat loud upon initial start up, but that is partially due to it being in the garage. Once it's warmed up it quiets down, and while I can hear it while driving around, it's not so loud that it bothers me. Then again, I'm not in the car that long, maybe 30 minutes at a time.

Having said that I've always planned on installing it because it cost too much to just let it sit on the shelf, and it would be great to have a few extra ponies. But the coupe cabin drone issue is always at the back of my mind, and I don't remember reading that it's every been resolved for fastback owners.


drone and loud are 2 different scenarios

and, 2.4 and GXP may also be different scenarios

Bill
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post #15 of 20 (permalink) Old 11-20-2018, 07:41 PM
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I have a 05 Nissan 350z that's my DD and HPDE car.

They make both down pipes and rear exhaust with those resonators on.



Down pipes. Used after the manafolds before the Y pipe in the 350z. Used in place of cat delete.


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