| On
the 931, the stock lower charge tube bracket is NLA from Porsche. It is
secured to the block using a 90° bracket as depicted in this
excerpt from PET (item #4):
From PET:
Illustration 107-30
The
two bolts that secure the bracket to the block have a tendency to back
out or shear off. We have seen many 931s where this bracket is
completely missing. Since the lower charge tube is only an
interference fit onto the turbo outlet, if this bracket is missing, the
car will suffer from massive boost leaks. Forced air exiting the
turbo causes the lower charge tube to lift off of the
compressor
outlet, resulting in boost leaks, dangerous air-fuel metering problems,
and dramatically reduced performance.
In early 2009,
we
collaborated with a 924board forum member to have a small run of
replacement lower charge tube brackets fabricated. These items were
plasma cut from .125" mild steel. The plasma-cut bolt holes are not as
clean as we would prefer, and the .125" steel is just slightly thinner
than the OEM 3mm material. However, these brackets are
completely
functional and in an area where cosmetics are of little concern. When
the current supply is exhausted, we will commission another run with
mounting holes drilled on a press. In the meantime, we are offering
these functional, if not pretty, replacements for reduced price.
We
recommend priming or painting these brackets for corrosion protection.
We also recommend using high-strength M8x20 bolts, since the failure
mode on the OEM version was bolt shear, presumably due to vibration and
fatigue. Lock washers should also be used, along with blue loctite to
minimize the likelihood of the bolts backing out.
| | CTB-001
Lower Charge Tube Bracket
3
available
For
1979-82 931
CTB-001
Lower Charge Tube Bracket
(original OEM part in background)
CTB-001
Lower Charge Tube Bracket
Comparison
of material thickness (OEM part on top) |
