Hi Gang-

My efforts toward eliminating inline 4 vibrations of the TiiCo kit became an obsession; but did produce some results.  First, regarding exhaust vibes, flex joints etc., I see by posts here that some kits had flex joints installed in the downpipe as delivered, some didn't.  Mine did. Though it had a flex joint, it was very stiff, couldn't possibly dampen vibrations. I had a race type ball & socket exhaust flex joint (btw:the typical VW connection w/the iron donut can't be made into a useable flex joint) kicking around (came from Techtonics, couldn't fnd it in thier online catalog though http://www.tttuning.com/index.html). I removed the flex joint that came installed, and  found it to be a type I had never seen before.  Outside is the same stainless wire mesh as usual, inside is spiral wound tubing like electrical BX cable.  Every flex joint I've seen is seemless corrugated tube on the inside like an accordian. No wonder it was so stiff.  Anyway, the ball and socket joint has been successful at interrupting the the transmission of vibes to the rest of the exhaust.  Problem is the joint is mild steel and will rust and seize sooner or later.  I plan to recreate the entire exhaust in stainless at some point and will use a stainless ball joint from Wicks http://www.wicksaircraft.com/showPage.phtml?pagenum=241.  Last tip for exhaust; I found that I had not used a "spacer" that TiiCo provided to move the right side exhaust mount more toward the center of the Van.  I installed it and found another improvement.  Something to do with frequency, vibration period etc. 

My last and strangest discovery was Sorbothane.  Yup, the stuff in the heel of your expensive running shoes. When I had posted to the list about trying stuffing the gaps in the motor mounts with foam, polyurethane etc., one response came back saying try Sorbothane.  Absolutely amazing stuff. Couldn't find it for sale in raw form, so I bought a Bell bicycle seat gel pad and cut 'er open.  To install it the mounts have to come out.  On the bench, I used a flywheel puller to open the gaps in the mounts.  This allowed an easier install of cut-to-fit pieces, and allowed the mounts to squeeze the Sorbothane a bit when released.  Sorbothane is strange stuff. It could make very convincing "alien flesh" at halloween. I had some fun grossing out my kids.

All of the resonant buzzing is now gone.  It's still an I-4 back there for sure, but the sound is consistent throughout the rev range.  No more brain scrambling peak at 4,000 rpm.  A side benefit of the Sorbothane: no more engine continuing to bounce after you hit a bump.  The rear end feels much tighter and more "tied down".

I did do some temperature extreme checks on this stuff.  All afternoon in our freezer didn't change it's consistency at all...ditto a drop into boiling water.  Should be OK year round. 

Now our TiiCo install is really fun.  I can wail it up to 5,500 rpm without wincing as I pass through 4k.

 

Gary