Date: Wed, 26 Feb 2003 21:30:26 -0500
Reply-To: Myron Lind <mdlind@RICA.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Myron Lind <mdlind@RICA.NET>
Subject: More diesel intake resonance
Thanks to all who offered ideas and photos regarding my last resonance
inquiry.
I have made a lot of changes, and have changed the resonance, but it is
still there. Any more "muffler" ideas?
Here is the current set up:
I fabbed an "intake box" out of 6 inch PVC, ala David Marshall (thanks,
David for the great description and photos). This is stuffed into the
passenger side cubby and wrapped in some B-Quite insulating foam. The air
comes out of the box and go across the back of the engine compartment with 2
1/2 exhaust tubing, cut and welded to fit around everything. Then, near the
drive side of the engine compartment it drops down and then forward into the
turbo. It has a total of three rubber connectors so it seems that I have
reasonable isolation between the turbo (motor) and the van body (air intake
box). "Seems" may mean that I don't have good isolation. Anyway, the air
come into the fabbed air box via two 2" PVC elbows that connect to two
original diesel vanagon air intake tubes. One tube hooks to the original
plastic "inlet" from the diesel vanagon, the other goes into a 2" diameter
8" long PVC pipe with various holes drilled into to hopefully help confuse
any sound waves that get set up. Both are right inside the passenger vent
right behind the rear side window. The original diesel intake is mounted
using several grommets to isolate from the van body. The PVC pipe is
insulated from the van body using a strip of B-quiet foam. The plastic vent
cover is not on at this time because the 2" PVC is in the way of the vent. I
have wrapped the metal intake piping and the fabbed air box with various
insulating materials. It is some quieter, but not enough. Wrapping the
intake piping did make the turbo whistle noise vanish. The motor is nicely
isolated from the carrier bars, has original and expensive VW mounts for the
alternator and AC, belts and pulleys are all aligned and straight, etc. The
exhaust piping does appear to have some vibration but no different than any
other diesel I have owned. I have a glass pack muffler attached same method
as original diesel vanagon. Exhaust tubing is various straights/bends welded
and connected with those Walker type stretch clamps that are about 4 inches
wide.
Here is the current noise situation:
The resonance seems to have moved up to the vent area, but seems very
persistent at finding it's way into the van. If I stand by the vent there is
a very deep throaty roar, not that different than before. Almost sounds like
a low pitched far away fog horn. Inside the van there is a low resonance at
idle that drowns out the motor noise. At various rpms it is not so bad. It
seems worst somewhere between 2800 and 3200 rpm--not sure exactly because I
don't yet have a tach. I am surprised by this, as I thought having two
"mufflers" of larger diameter, a different sized air box, and yet a
different size pipe between the air box and motor would have helped to
eliminate some of this noise. Adding a layer of insulation and the rear bed
did not significantly change the noise level (if it changed at all), nor did
swapping the metal deck lid with a fiberglass one.
So, any other ideas before I start trial and error?? Or, any sound wave
experts who can shed some light on how do reduce the noises??
Thanks for any help
Myron Lind
1982 Westy TDD/5 speed
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