: What are possible causes of exhaust resonance?



Playdrv4me
04-16-08, 10:56 PM
This is relating to the H2...

I've noticed ever since I picked it up that the exhaust drone is QUITE loud at exactly 1500RPM. It practically doesn't do it at all when it's cold, but once it warms up the exhaust makes it a little uncomfortable in the cabin, especially since 1500RPM falls right in line with about 45-50mph which is where most driving time is spent.

To the best of my knowledge this is the stock exhaust and has not been modified. It does sound kind of throaty when you listen to the idle, moreso than I remember my Escalade being.

Ideas?

I~LUV~Caddys8792
04-16-08, 11:30 PM
It's probably just the way the exhaust is manufactured. My S320 has a constant intake drone at 2500 RPM. At 2400 it's not there, and at 2600 rpm, it's not there. Which sucks because 70-75mph usually falls in right at 2500 rpm.

dkozloski
04-16-08, 11:42 PM
That's why a Caddy has exhaust resonators; to dampen that kind of noise.

Jesda
04-16-08, 11:48 PM
Is the noise coming from front or rear? You may be able to alleviate it with exhaust modifications.

Playdrv4me
04-17-08, 12:11 AM
Is the noise coming from front or rear? You may be able to alleviate it with exhaust modifications.

Definitely an exhaust sound, you can even hear it trail off when you release the pedal. Couldn't really pinpoint exactly where.

EcSTSatic
04-17-08, 08:36 AM
Definitely an exhaust sound, you can even hear it trail off when you release the pedal. Couldn't really pinpoint exactly where.

FWIW - Drivetrain sounds will die off too once torque is reduced. i.e. you let off on the gas.

Playdrv4me
04-17-08, 09:50 AM
FWIW - Drivetrain sounds will die off too once torque is reduced. i.e. you let off on the gas.

Yea I thought about that already, it's definitely the burble of the engine you can hear dying off when you let off the gas though.

Submariner409
04-17-08, 10:07 AM
Exhaust resonance is the moving example of an organ pipe: the frequency of the gas pulses from the engine excites the exhaust pipe length as a function of "tuning". By experimenting with tailpipe length and diameter it is possible to move the resonant tone quite a bit up and down the engine rpm scale. Back in the old days, with a set of true duals using glasspacks on, say, a Chevy Impala 327, you could tune the rpm range of the power "rap" not only on the way up, but also on the coast-down rap by using longer or shorter tailpipes. That art is all but dead in today's instant gratification world.

Resonance tuning is why the CORSA systems can perform as quietly as they do at part-throttle cruise, with absolutely no baffles or packing anywhere in the system: it's all straight pipe, so no flow restrictions, none, nada, nowhere.

Rolex
04-17-08, 11:55 AM
A quick and inexpensive fix would be one of the cone shaped resonaters that can be fitted into the tail pipe. They reduce noise and drone significantly without hurting performance. I think zoomers makes one, but I know I saw some in the Summit catalog yesterday.

dirt_cheap_fleetwood
04-17-08, 12:16 PM
At least you can fix your problem relatively easily. I am stuck with that damn main bearing thump for life.

Playdrv4me
04-17-08, 01:03 PM
At least you can fix your problem relatively easily. I am stuck with that damn main bearing thump for life.

Well, I'm hoping the exhaust resonance is not the symptom of some sort of engine problem.

Playdrv4me
04-17-08, 01:04 PM
A quick and inexpensive fix would be one of the cone shaped resonaters that can be fitted into the tail pipe. They reduce noise and drone significantly without hurting performance. I think zoomers makes one, but I know I saw some in the Summit catalog yesterday.

I'd be interested in finding out more about this if you locate it!

Thanks!

Rolex
04-17-08, 05:32 PM
http://store.summitracing.com/egnsearch.asp?Ntt=dynatech+vortex+cone&x=0&y=0&searchinresults=false&Ntk=KeywordSearch&DDS=1&N=700+115

Worth a look. :)