Re: Wastegate Diaphrams

[orin@netcom.com (Orin Eman)]

> 
> >I'm looking into manufacturing these...
> 
> >Who would be interested if I can get the price down to around $75
> >each?
> 
> 
> >From my understanding, all turbos will need one sooner or later. If this is the
> case and they are as hard to get as everybody says, I'll be in for one (or
> course it needs to work on my car)

So far I've looked at two wastegates, the one on my car, an 86 5kCSQ and the
one I got from the junkyard.  The junkyard part seems to be an older part from
the date on one of the castings.

Time for some bad ASCII art.  The junkyard wastegate actually has two diaphrams,
arranged as follows:


     __C                 C__
     ||C                 C||
_____||C       SS        C||_____ Upper diaphram
_____ |C      NSSN       C| _____ Lower diaphram
     ||CCCCCCCCSSCCCCCCCCC||
     ||________SS_________||
     |_________SS__________|
     PPPPPPPPPPSSPPPPPPPPPPP

Key:
C - metal cup
N - nut
S - shaft to actual wastegate
P - support plate

The wastegate from my 86 only has the lower diaphram.  The upper diaphram
I have has two holes at it's weakest point, the 180 degree fold.  I suspect
this is the first failure point.  Both lower diaphrams are weak at the upper
90 degree bend and mine had a small tear here.

The metal cup and support plate are identical between each wastegate.

I don't believe the upper diaphram is necessary - the diaphram(s) are not
providing support for the structure, most of the upward force is provided
by manifold pressure against the support plate, downward force is from the
spring and sideways by the shaft in its bore.  The diaphrams are flexible
but do not stretch.  In addition, I believe the upper diaphram will always
fail first due to the extreme fold.  The two diaphrams are not in contact
with each other at their respective failure points, so they don't
reinforce each other's failure points.

SO, I am investigating manufacturing the lower diaphram, fitted to the cup,
the same as exists in my car.  This should fit most all Audi wastegates
and be as reliable as the two diaphram system.  Maybe there is better
material I can use...

As far as the economics are concerned, tooling will be expensive, but not
too bad for the lower diaphram.  I don't want to think about the upper...
Once the tooling is done, each diaphram will be very cheap.  I should have
an idea how much tomorrow.

Hope that helps!

Orin.