[jwmarc]

To any and all.....

I have a 930 turbo and would ask the assistance of the board to provide me with a little tutorial on the operational elements. I have read a book ( read not studied) about turbos.. Corky Bells Maximum Boost.

So here goes.. As air enters the air cleaner housing and moves the CIS air/volume plate ( feedback to the FD head) it passes out the bottom and into the ducking which attachs to the BOV plenum housing. This plenum is massive and I removed it recently to replace the plastic O rings which muffle the slamming of the internal cylinder piston part. The air flow continues to the air inlet side of the turbo and passes ithrough the compressive outlet which then passes into the intercooler and then exits into the throttle body/ intake/cylinder manifold. When not under boost does the air bypass the turbo/ through the BOV plenum which feeds directly into the throttle body/intake manifold ? when boost spools up the air takes the longer route through the turbo/intercooler route.... The BOV operates when I punch the throttle I can hear the ram hitting the plastic O rings. At what point does the BOV operate when running and under boost? Can someone describe the Porsche BOV implementation?

I have heard/read that you can do away with this massive plenum and BOV by installing something like a KoKeln intercooler. Does the after market approach detract from the legacy engineering...Why did Porsche make such a huge assembly for this arrangement? Was it the state of the art in 1987?

The boost pressure switch that connects to the yellow over boost relay switch and cuts out the fuel pumps. At what pressure level - what PSI ? ( it sits in the intake manifold or BOV plenum..I cant remember). Could someone explain the operation...... At this point I would like to acknowledge Mr. John Walker who responded to a post about fuel cut-off and directed me to the overboost relay as a culprit... sure enough under a microscope there where cracks and fissures in the solder welds which I re-soldered and havent had any more random fuel cut-outs and side of raod events...Mr. Walker thank you again.

AFR is a function of the fuel metering spec associated with the FD head and air volume plate. The frequency valve dumps more fuel based on lambda feedback. What are the contolling conditions of this? I am comfortable with the CIS operation basics but had a question about the fuel enrichment relay... is this the power source to the frequncy valve? is it the control for the cold start injector? Does the CIS controller have anything specific to Turbo based CIS Porsches?

I know I have thrown allot out ..I will welcome responses., and will appreciate your advise....