Date:         Sat, 8 Mar 2008 19:58:44 -0800
Reply-To:     sam mccarthy <sfcompost@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         sam mccarthy <sfcompost@YAHOO.COM>
Subject:      I4 conversion exhaust
Content-Type: text/plain; charset=iso-8859-1

Neil, with my I4 vanagon I had 2 different exhaust designs with radically different results.  The first set up I had built at a exhaust shop using an old Dasher dual outlet manifold, which angles toward the front of the van. I had the shop follow the example I had seen on a German engine conversion site which ran the exhaust forward through the aircooled heater tube hole, forward to a muffler hung under the center of the van, into a 180 degree bend back toward the rear and then out to the driver side ahead of the rear wheel. This required a simple layer of sheet metal as a heat-shield to keep the heat away from the floor, but worked very well and was almost too quiet.  No vibration problems whatsoever.  My only concern was that the cat was a bit too close to the transaxle. And, I liked having the exhaust coming out of the side of the van, as it told those discerning van-heads that this was no normal air-cooled van.
When that exhaust began to fail, I had the same shop build another one. When I requested they build it further away from the transaxle, they suggested going to the stock location, and thought they could do it for similar costs.  It was a mistake.  Not only is this a much more costly design to construct, but vibration problems are a too often occurrence.  It took three redesigns, and a lot more cash before the vibrations and resulting cracking were solved.  And, with the short length of the stock design, it is often quite loud. I think the secret really is using a flexible coupling between the downpipe and the bend to the back of the van, and using rubber hangers to suspend the system along the back of the van.

With my TDI install, I would rather go forward once again, but the 1990 body I'm using, there is no heater tube hole to route through. I'll have to go rearward.
If you are looking for the right manifold to use, take a look at Frank Grunthaners' post in the archives, or within Vanagon.com as he has done extensive testing on the various possibilities and found that the Audi 80/90 dual outlet manifolds are the best.  The Dasher manifold I used worked well, but doesn't flow all that well.
Good luck, I hope this helps,
Sam M