MonteCarloSS.com
Previous Thread
Next Thread
Print Thread
#1057651 - 06/05/18 08:10 PM Exhaust Drone Eliminated!  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
I've been struggling with a vibration between 50-65, that made the car un-driveable! After a lot of work on the rear, differential, brakes, engine, etc, I finally got vibration down to a 2000-2300 rpm area, not speed related. Figured this had to be drone, so I tried adding a Helmholtz Resonator. Nothing to lose! Well, it worked. It reduced my drone and vibration in that RPM range by over 90%. Like night and day difference. If you are experiencing this, I can recommend trying it. It's not hard or expensive, and it might help your situation.

My exhaust is a fairly stock MCSS exhaust, with CAT. The mufflers are Dynomax VT's. I think the valves in them have failed, as I didn't have the drone in the beginning. That may be my next project... The Resonator started life as a piece of 2.25" exhaust pipe, about 2" long. You will also need a piece of 2.25 ID exhaust pipe, about 12" long, to slide over the first pipe, for tuning. This shorter pipe needs to be capped. I cut two slits in the end of the short piece, so a regular muffler clamp could be used to tighten it on the longer piece. It can be slide on the longer piece to fine tune the resonance ( think about a trombone slide).

A hole was cut in the exhaust pipe just after the cat, and the longer pipe welded in. I had an exhaust shop do this, and they were able to put a couple of slight bends in the pipe so it lined up next to the stock exhaust pipe. It was only $80, and I bet it could be done a lot cheaper. If you've got the tools and inclination, easy to do at home. It's important the this pipe be welded onto the stock exhaust at 90 degrees. You want the exhaust passing over the opening of the new pipe to create a sound tone ( like blowing on a coke bottle). That sound will be the same frequency as the exhaust drone, but exactly 180 Degrees out of phase. The two sounds then cancel each other out.

Slide the shorter pipe over the longer one ( you might have to do this before welding!), and measure the overall length. Make some marks on the longer pipe, where the shorter pipe overlaps it, at the 28-31" overall length mark. This will give you some marks to use as you do the fine adjusting to get just the right tone. Start at 28", and take a test drive. Note the vibrations and feelings. Then move the pipe to 29", then to 30", then to 31"... you'll finally get a distance that feels pretty good. At that point, move back and forth over that point in 1/8" increments, until you find just the right spot! My sweet spot was at 30", and I finally settled on 30 1/8" as the best I could get.

Once I'm completely happy, I may add an exhaust cutout on the end to replace the cap spinning

[Linked Image]

[Linked Image]

[Linked Image]


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057652 - 06/05/18 09:19 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Apr 2011
Posts: 883
Hunter79764 Offline
Member
Hunter79764  Offline
Member

Joined: Apr 2011
Posts: 883
Grand Prairie, Tx
Nice solution, and kudos for tracking it down. Just curious, do you think capping it with a slash cut piece instead would widen the effective range and make the exact location less precise?


Sometimes you just need a bigger hammer...

'85 MC with budget 5.3L swap, TH350 with stock 2.14 rear end
It ain't much off the line, but it's nice on the highway
#1057653 - 06/05/18 10:35 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: May 2016
Posts: 424
Witness86SS Offline
Member
Witness86SS  Offline
Member

Joined: May 2016
Posts: 424
Hatfield, PA
Science is awesome!


Justin
1986 Black SS
350 L05 - Hooker Longtubes - FlowMaster True Dual 2.5" - Electric Cutouts - Electric Fans - Transcooler
#1057656 - 06/05/18 11:45 PM Re: Exhaust Drone Eliminated! [Re: Hunter79764]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
Originally Posted by Hunter79764
Just curious, do you think capping it with a slash cut piece instead would widen the effective range and make the exact location less precise?


Not really. 1) the sound has to bounce back out off the end of the pipe, so I don't know if a slash would work. The "tone" is based on the total volume of the pipe- hence the need to adjust the size. You could make it out of 4" or 5" pipe just as easily, but the length would be much shorter.


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057659 - 06/06/18 02:27 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: May 2009
Posts: 1,833
Richie Cat Offline
Member
Richie Cat  Offline
Member

Joined: May 2009
Posts: 1,833
Lake Ronkonkoma, N.Y.
I wonder if you had put a balance tube between the two intermediate pipes, it might have solved the "vibration/drone".
Not a fan of that extra leg just hanging there with no rear support on it.

Last edited by Richie Cat; 06/06/18 02:28 PM.

83 SC, 355 w/TPI
#1057660 - 06/06/18 02:36 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
Supposedly the two headers running into the cat should do the same thing as an H-pipe for balance. This was the normal fix for the Dynomax VT mufflers to keep the valves from fluttering. I think my valves may have stuck open, since I didn't have a drone issue when they were first installed. So next project is to cut the mufflers open and see. I may weld the valves closed. If that doesn't fix the remaining balance of the drone, then I'll likely change the mufflers. Didn't have the issue with the stock MCSS mufflers, so may go back.

I needed to leave the leg "unattached" so I could do the tuning thing. Once I'm happy, then I will attach a support strap over to the stock exhaust pipe. Haven't done this yet, because if I have to change the mufflers, it's likely that I will have to re-tune the resonator.


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057661 - 06/06/18 06:09 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: May 2009
Posts: 1,833
Richie Cat Offline
Member
Richie Cat  Offline
Member

Joined: May 2009
Posts: 1,833
Lake Ronkonkoma, N.Y.
Originally Posted by 87ChooChoo
Supposedly the two headers running into the cat should do the same thing as an H-pipe for balance. Didn't have the issue with the stock MCSS mufflers, so may go back.


Then I think you should. Maybe the aftermarket mufflers gave up the ghost.
And yes the Y connection splitting one into two is a type of "X pipe" after the Cat.

Last edited by Richie Cat; 06/06/18 06:10 PM.

83 SC, 355 w/TPI
#1057702 - 06/10/18 02:30 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: May 2007
Posts: 4,601
Buick Runner Offline
Member
Buick Runner  Offline
Member

Joined: May 2007
Posts: 4,601
Dharma station 1 the Hydra
That spliter, even without the welded on third tube is a lot different from the spliter in my exhaust.

[Linked Image]

Maybe there are two styles of post cat exhaust y pipes available for these cars?

Last edited by Buick Runner; 06/10/18 02:31 PM.

SBC powered 1987 Regal with TES headers, ZZ4 intake, ZZ4 PROM chip, mini starter, THM2004R, 2500 stall converter, 2040 cam, CCC system, and 3.73 posi rear.

2008 ex NPS P71 Crown Victoria, cop motor, cop shocks, cop brakes.

Never argue with an idiot.
They will just drag you down to their level and beat you with experience.
#1057703 - 06/10/18 02:51 PM Re: Exhaust Drone Eliminated! [Re: Buick Runner]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
Originally Posted by Buick Runner
That spliter, even without the welded on third tube is a lot different from the spliter in my exhaust.


That is quite possible. The Vehicle I drive is an El Camino, but the guy I bought it from had an '87 Aerocoupe. He installed the Aerocoupe Engine and exhaust into the Elky. I know my pipes have an extension just ahead of the muffler, to account for the different wheelbase, but I thought the balance of the system was just stock Monte ( I have no other point of reference). Same principle would apply to yours, but you would likely need two resonators- one for each side.

Sorry to all if my system is different from stock. I figured this would be the only G-body forum I frequent where this might work brick


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057704 - 06/10/18 05:31 PM Re: Exhaust Drone Eliminated! [Re: Buick Runner]  
Joined: May 2009
Posts: 1,833
Richie Cat Offline
Member
Richie Cat  Offline
Member

Joined: May 2009
Posts: 1,833
Lake Ronkonkoma, N.Y.
Originally Posted by Buick Runner
That spliter, even without the welded on third tube is a lot different from the spliter in my exhaust.

[Linked Image]


You can see where one is a Y pipe, where the other is a one into two configuration which would help with harmonics (header theory)
His work was done to help this, but again I think adding a balance tube would been a simpler route to go for his exhaust.


83 SC, 355 w/TPI
#1057708 - 06/10/18 08:34 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
well, I still haven't resolved all of the resonance issue, so I may go back and try a balance tube. I definitely believe in the balance tube when you have true dual headers. I always thought that having two headers dumping into one cat, that the cat would tend to blend the pulses and thus the balance tube would have been superfluous.

One other possibility, for which your opinions would be appreciated. My system is currently hung with only 1 support aft of the muffler on each side, and one support at the tip of the tailpipes ( stock MCSS Tailpipes and brackets). There is no support at the cat ( I know stock there was one that came over from the trans mount). I'm thinking adding one or two additional supports each side wouldn't hurt?? Maybe one just in front of the mufflers ( maybe half way from the muffler to the Y at the cat, and then one just aft of the Cat Converter?? ( 3 more total?)?? Thoughts?


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057709 - 06/10/18 08:55 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
I was looking at the Walker Exhaust catalog, to see if they had a bracket for the cat, and noticed that their diagram of replacement exhaust parts showed the y pipe like the one I have- 1 pipe coming off the cat, turning almost 90 degrees, and then the two pipes to the mufflers coming off that pipe. That is different from the one showed above, where the two pipes coming out of the cat come out as a Y, splitting directly at the cat. That style of Y is certainly a more performance oriented method, and may be an aftermarket system??


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057735 - 06/12/18 03:14 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Jul 2003
Posts: 9,188
SickSpeedMonte Offline
10+ Year
SickSpeedMonte  Offline
10+ Year
Member

Joined: Jul 2003
Posts: 9,188
MD
Very interesting!

My post-cat y-pipe looks like the one in the OP. Both my '85 and '86 SS stock systems were like that. I think the other style might be aftermarket.

I have a terrible drone with flowmaster 40 series mufflers. Where my 1 to 2 junction is, the weld broke and the car is currently down until I can get to it. I was thinking about changing to 50-series delta flows, but for the price, this might be a better option. I can do all the welding at home. I had the same thoughts about a balance tube and I also felt that it would be superfluous. I think the problem is just the resonant frequency of the exhaust volume matching up with the driving frequency from the engine. You could do the same thing by making the tailpipes longer or shorter, but I think that's harder to do and still have it exit where you want.

So do you still feel that you reduced 90% of the drone?

#1057736 - 06/12/18 04:32 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: May 2009
Posts: 1,833
Richie Cat Offline
Member
Richie Cat  Offline
Member

Joined: May 2009
Posts: 1,833
Lake Ronkonkoma, N.Y.
If you want to get creative build an X pipe and see the difference. I always had H pipes on my cars and it really didn't matter where that junction was. The car I have now I made up a X pipe. The sound is more "mellow" with it. Yes I'm running true duals without cats. Not the same boat as you. But isn't hot rodding what it's all about?


83 SC, 355 w/TPI
#1057737 - 06/12/18 04:36 PM Re: Exhaust Drone Eliminated! [Re: SickSpeedMonte]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
Originally Posted by SickSpeedMonte

So do you still feel that you reduced 90% of the drone?


I still have just a little drone that starts exactly at 2000 rpm, which for me is about 55 mph. It causes just a little vibration, but nothing I couldn't live with. It is significantly better than it was. I can induce the drone easily by just moving the Helmholtz 1/4" either way, so I am sure it is helping. I can induce the same drone in 3rd gear at 2000 rpm as well, but the internal vibrations are much less. Getting new tires today, so we'll see if that helps too ( reported failures on the Firestone's I'm running). The vibrations could be speed related because of a tire being bad, and just coincidental. Tires get hard here after about 4 yrs, so time to change them anyway. This process is like peeling an onion!

The resonance was at 107hz, now it is at 70 hz, and a much lower DB. ( I use an app on my Android- "Spectroid". It allows me to see audio signals real time). I think my issue now may be with the choice of muffler ( Dynomax VT). The valves in them may be failing, so that is going to be my next resonance "fix". I also think I may need more supports ??( see above post). I'm going to keep chipping away at this until I get it fully resolved.

All that being said, I have heard so much about the Flowmaster 40's being bad on drone, I'm not sure how much it may help. I have seen some other posts where it did a very good job, and the cost is so minimal it's certainly worth a try. Since you have welding capability, cost may only be $10-20 for pipe. If it doesn't work, just cut it off and cap it ( or put in a cutout yup ) .


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home
#1057744 - 06/13/18 11:56 AM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Jan 2002
Posts: 1,263
basemonte Offline
15+ Year
basemonte  Offline
15+ Year
Member

Joined: Jan 2002
Posts: 1,263
Old Bridge, NJ
Have the daughter's Monte/SS with a Walker cat back system, (2.25 dia tube), and never any drone issue with Flowmaster Super 40's.

My A body Malibu uses 2.5 tube, Dynamax (Walker) Super Turbos, also with no drone issues.

Both use Edelbrock TES headers and gutted stock Monte SS bell mouth converters.

Neither use the factory converter support.

#1057800 - 06/15/18 10:43 PM Re: Exhaust Drone Eliminated! [Re: 87ChooChoo]  
Joined: Oct 2003
Posts: 1,472
87ChooChoo Offline
10+ Year
87ChooChoo  Offline
10+ Year
Member

Joined: Oct 2003
Posts: 1,472
las Vegas, NV
More news! I was doing more research, and one site suggested installing under-hood insulation. I had removed mine when I installed my Cowl Induction hood, so I figured - why not. 5 minutes later, I went for a test drive, and WOW- another big reduction in drone. I still have just a little drone, but nothing like before. I could live with it as is, but I am going to keep pursuing the holy grail.

Today, I visited a Performance Exhaust shop to ask their opinion. They suggested installing a couple of Glasspacks in front of the mufflers. I asked if they could go at the tip of the exhaust pipes, but they said they would do more good before the mufflers. So I'm going to order a couple and see what happens.


85 El Camino Choo Choo with L31 350 Crate, TPI, Serp, TES Headers, GN 200-4r, 3.73 8.5 GN Posi, Acura Buckets, '04 GP Console, Electric Mirrors, Electronic HVAC, ZQ8 wheels, Blazer front brakes, LS1 rear brakes, and more....
https://sites.google.com/site/darbyselky/home

Random Images
784/thumbs/MiniTub2.jpg
by John B
550/thumbs/c4_3.jpg
by stonecoldtim
939/thumbs/IMG00015.jpg
by ehgn87
500/thumbs/IMAG0175-1.jpg
by 8phil8
500/thumbs/CAM00141.jpg
by JMonte7892
Help MonteCarloSS.com


Recent Contributors
Rob Forbes
techjay

Site Maintenance Fund
Annual Server Fee
Fund Raiser

FrankOC
ratbuddy
mmc427ss
FinallySS
witness86ss
Gbguy
WB of NOLA
Tomh115
oemtech
CDN87EH
Fred_SS
thepezking639
Chevelle502
Akron Aero
Pacheco
Crusher
MC87SS
cwest01
Jayhawk88
stew'86MCSS396
Hey-O
1987 T56 AEROCOUPE
spoon
PA85SS
dns87ss
Kawaiikeno
86ttop
Mikes84
wilsoab
wreckrunner
intmdatr3
Bubsy83
Authorized Vendors
Tell them you saw it
on MonteCarloSS.com!


CustomMonteSSParts.com
Dixie Monte Carlo Depot
GSI Interiors
HRpartsNstuff
Mikes Montes
Savitske Classic & Custom
Powered by UBB.threads™ PHP Forum Software 7.6.0