injection timing

[Wilkrod at aol.com]

Hi Dan,

To answer your question pop off valves are simply spring loaded trap doors on
the inlet tract. Porsche 911 is the first car that comes to mind which uses
them, although I believe they are aftermarket. Positive pressure in the
intake plenum caused them to pop open venting the pressure prior to damaging
the plenum.

I believe they were only required on the early C.I.S. cars, what happened
usually was after a cold start the engine was shut down prior to warm up, and
then restarted. This resulted in additional fuel from the cold start injector
causing an extremly rich mixture which would explode in the air intake
plenum.

If you are interested I can give you the names of some aftermarket companies
which sell a generic valve which can be inserted in a plenum.

Regards
Jeff