The shielded stovepipes described below are designed to preserve and extend the life of a new or good used upper intake manifold (UIM) that is not protected with a metal sleeve (heat shield) in the EGR bore.
1995-2003 non-supercharged GM Series II 3800 engines (Regular Production Option L36). Large base pipe fits 95-98; smaller base fits 99-03.
Techinfo article 38 provides the background and current repair options for L36 owners contemplating repair of their (UIM) and lower intake manifold (LIM) gaskets. http://www.bonnevilleclub.com/forum/...e=article&k=38
While I recommend the APN UIM mail-order repair kit as the best off-the-shelf fix for this common problem, I understand that many are not willing to invest $115 to purchase the APN kit in advance or are unable to wait on the part to be shipped when the UIM or LIM gaskets fail. The result is that most owners buy a replacement Dorman UIM kit (for about $150) from a local parts supply house like NAPA or Autozone when they experience a failure. The problem is that unlike the APN, the EGR bore of the Dorman is not protected with a heat shield. The shielded stovepipe offers a lower cost, advance purchase option that raises the quality of the Dorman repair to a level comparable with APN.
The addition of a shielded stovepipe makes the widely available Dorman UIM repair kit a much longer-lasting repair option. By combining in one component a reduced diameter aluminum stovepipe and a stainless steel heat shield for the plastic EGR bore, the most critical features needed for a long-lasting UIM repair are provided. These beautifully made prototypes and several more were machined by Bonneville Club member Bob Keyes from the drawing below. (Thanks Bob!)
A few of these shielded reduced diameter EGR stovepipes will be made available upon the successful completion of some in-vehicle tests. Marketing options will be pursued if there is sufficient demand. Estimated cost: $25 or less.
A thin-wall stainless steel heat shield is pressed onto the machined shoulder of a one-piece, machined aluminum stovepipe. Bob Keyes solved the problem of securing the shield in place by dimpling the base of the shield into the aluminum shoulder with a sharp center punch.
This design offers the following advantages:
1. Because of the shield'* tight fit and the direct contact of the base of the pipe with the LIM bore, both the pipe and the shield are cooled by conduction by engine coolant. Aluminum, the same material used by GM for 99 and newer stovepipes, is a better heat conductor than steel used in other designs.
2. The one-piece stovepipe design allows installation by simply driving the top of the pipe into the LIM bore.
3. The insulating gap between the hot pipe and the integral heat shield is 0.100". This is .030" larger than the gap provided in 99 and newer engines by GM.
4. The shield protects the vulnerable plastic EGR bore of the UIM without the need to cut away any plastic between the EGR bore and the coolant passages.
5. The top of the pipe is exposed to allow intake air to cool the top of the hot pipe, yet the shield effectively covers the plastic EGR bore in the UIM.
6. The shield extends to the deck of the LIM thereby providing protection for the LIM/UIM plastic frame gasket.
7. Installation of the shielded pipe only takes a few minutes and it can be placed in service immediately.
Thanks to Bob Keyes for his excellent machine work; thanks to Archon and MyLittleBlackbird for their help in testing prototypes.