I think it is illusory to try to get a 100% sealed exhaust system. Metal to
metal
joints are not perfect, especially when they are subjected to thermal expansion
and vibrations. They can be improved using some sort of sealant but that
will not last for long due to the huge temperatures involved. Leaks are more
likely
on the 914 due to the higher back pressure caused by the turbo when it is
working at full boost with the waste gate fully closed. Leaks are also likely
on the 912 with the CKT exhaust when the springs age and become weaker.
One solution to prevent fumes to get into the cockpit is to make sure cockpit
pressure
is always higher than both cowling pressure and outside pressure. To achieve
that, the cowling should be well vented with small air intakes and an exit
area big enough to suck the airflow. Fresh and/or heated air vents should
be at least partially open to create a pressure build-up inside the cockpit. I
still have to perform some CO measurements to determine if I was successful at
achieving that.
Remi Guerner
F-PGKL
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