Re:<E28> Exhaust - catalytic - recommendations?

[Robert T Chafin <rtchafin@xxxxxxxxxxxxxx>]

At 09:57 AM 8/25/98 -0400, Kim Hensley wrote:
>Date: Tue, 25 Aug 1998 06:45:34 +0000
>From: khensley@domain.elided
>Subject: <E28>  Exhaust - catalytic - recommendations?
>
>On my 1985  535i  I need to replace the exhaust from the end of the 
>exhaust manifold back.  What's there has rusted out.  For the last 
>"half" of the exhaust I plan to use a stainless steel system 
>recommended by some of you.  For the first "half" - which includes 
>the catalytic converter - what do you recommend?  And what about the 
>oxygen sensor?  Thank you for your time - private replies are fine.
>

Best material for the front half of the system, the so-called 'hot end', is
also stainless steel, but not necessarily the same grade as for the rear.
Front end requires high temperature strength, and, depending on where you
live (whether or not you drive in salt), it may require hot salt corrosion
resistance.  For unsalted areas, 409 or 439 stainless are fine materials
which are usually much less expensive than the austenitics like 304, 321,
309, etc.  The 409/439 steels also are very resistant to intergranular
corrosion,  something that most of the "pretty" stainless steels like 304
are very susceptible to (but 321 is NOT susceptible to). If available, an
aluminum-coated 409 or 439 would be a superior material for the 'cold end'
(Aft of the converter) also, deriving wet-salt corrosion resistance from
its' aluminum coating, while still having intergranular corrosion resistance.
Cost no object?  321 all the way, and you can even polish up the visible
parts.  Its' only drawback (aside from cost that is) is that it will
heat-discolor.   301, 302, 304, etc are to be avoided, because of the
distinct possibility of intergranular corrosion.
If you are using clamps instead of flanges or welds for your joints,  use
Heckethorn (also known as "Heco") guillotine-style clamps; no other clamp
will seal on stainless. None.  And tighten the clamps to 40-50 ft-lbs (yes,
 40-50 ft-lbs). Removal will require your basic blue-tipped wrench, but the
clamp won't let you down.
- - Robert

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