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exhaust noise - solved

Started by flyinlow, November 17, 2008, 07:13:16 AM

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flyinlow

I am working on a cycling noise at 60mph. Maintaining speed (2500-2700rpm). Makes the same noise at those rpms in second or first gear. If you accelerate or coast noise stops. Turn off engine at 70mph and coast thru 60mph,quiet. Engine and exhaust installed in May (3000 miles ago), Did not make the cycling noise at first. Noise first noticed two months /1000 miles ago. Exhaust close to body,but does not touch.

73 Charger/446/auto/schumaker poly mounts/3in. jegs exhaust/magnaflows/jegs bullet mufflers used as resonators/headers.

Checked converter bolts,transmission bolts,no change
installed h-pipe, mellower sound
swapped 3.55 for 3.23 carrier, no change
Axle adjusters crosstread ed, replaced axle bearings with Green bearings, no change
put different exhaust hangers on, no change
Dove car with left /right side plugged ,less exhaust sound, still cycling


ideas?

acelondon

my car makes what i would call a cycling noise around 1800RPM, but its the water running through the heater core.

does is sound like water flowing through pipes?

try to describe it a little better, maybe even record it, and i think we will be able to help better.

flyinlow

Noise sounds like a twin engine airplane with its engines out of sinc. A beating or cycling sound at about 2 cycles per second. Seams to originate from the muffler area.

Normal exhaust tone is there,but this is on top of that.  55-65 mph.  I live 20 miles out of town so everytime I go somewhere I get to hear it alot.

You here it at steady  speeds, light throttle. There is some gear noise (normal) at around 45mph.

Years ago I had a similar noise in a BB Fury. It was trans to engine bolts had loosened. Checked that and converter bolts.

Will look for a way to record it.

Frustrating

thinking about trying an x pipe


flyinlow

Car has a/c with heater control valve shut . put clamp on heater hose ,same noise.

Thanks for the idea!

acelondon

long shot, maybe its like an organ, and one of your pipes is "out of tune"

no idea how u'd fix it. You have matching mufflers?

flyinlow

Same magnaflow mufflers both sides. Same resonators. pipes look about the same length.

I pluged each side with a dog food can and drove the car with the H-pipe acting as a y-pipe with all the exhaust going out a single side.

Car was quieter ,still pulsated..

mikepmcs

I agree, i think its a harmonic issue with the exhaust.
Life isn't Father Knows Best anymore, it's a kick in the face on a saturday night with a steel toed grip kodiak work boot and a trip to the hospital all bloodied and bashed.....for reconstructive surgery. But, what doesn't kill us, makes us stronger, right?

resq302

I also get the same kind of thing like a low flying airplane type nose.  I have found that if you have a solid mounted fan, in my case, a 7 blade fan, the fan is basically just that a propeller.  At certain air speeds, the fan can or will make that noise.  With a clutch style fan, this can not happen cause of the slipping and such involved with it.  Also had the same thing happen on my 85 Jeep.
Brian
1969 Dodge Charger (factory 4 speed, H code 383 engine,  AACA Senior winner, 2008 Concours d'Elegance participant, 2009 Concours d'Elegance award winner)
1970 Challenger Convert. factory #'s matching red inter. w/ white body.  318 car built 9/28/69 (AACA Senior winner)
1969 Plymough GTX convertible - original sheet metal, #'s matching drivetrain, T3 Honey Bronze, 1 of 701 produced, 1 of 362 with 440 4 bbl - auto

Steve P.

Back in the late 80's - early 90's Toyota or Honda had an issue like this and the fix was to cut out a section of exhaust pipe and replace it with a flexible joint. It was about a foot or more long and it did work.. It sort of looked like a rad. hose with stainless wire mesh around it.  I hope that isn't the case with yours as it would look like crap.
Steve P.
Holiday, Florida

firefighter3931

I've been thinking about this one for a few days scratching my head. Could it possibly be a lean surge issue with the carb ? Perhaps the timing curve needs some adjustment ? Are you running a vac advance ? Light throttle misfire ?

Interesting that the noise occurs under load, only.  :scratchchin:


Ron
68 Charger R/T "Black Pig" Street/Strip bruiser, 70 Charger R/T 440-6bbl Cruiser. Firecore ignition  authorized dealer ; contact me with your needs

flyinlow

Take away my Mechanics licence.

It was the alternator.

I installed a Jegs 100 amp alt. along with dual electric fans shorty after the Mopar Nationals. This is a single wire delco alt. It charges great, its chrome, and less than half the price of  a single wire 75 amp mopar alt.

It must be out of balance. It beat up the bearing in 1000 miles. Was not noisy under the hood.

Noise transmitted to rear of car. Sitting in the car it sounded like it was coming from the muffler or rear axle area. 

Still do not know why it was load sensitive.

Jegs replaced the alt. and the noise is gone.

my troubleshooting skill must really be rusty. I spent hours chasing this one.



Hey , thanks for all the ideas submitted!     :2thumbs:

FLG

You know and i was just going to mention if you had your muffler bearings recently serviced. But glad you solved the problem  :cheers: