Tim968

Attached pic shows the diaphragm valve that drafts air through the carbon canister to the intake. Paul and Theo describe this as follows;
Operation: A diaphragm valve controlled by the throttle valve is located in the line off the carbon canister. This valve is operated by the LH ecu when he engine is at operating temperature. At idle, no vacuum is applied, and the valve is closed. When the throttle valve is opened, vacuum is applied at the diaphragm valve, causing the valve to open and allowing the gases to escape to the dia- phragm valve. This valve is timed by the LH control unit with a frequency of 6 Hz. Similar to the trigger signal of the injection valves, the duration of this signal is dependent on the intake air flow rate. When the intake air flow rate is low, the tank ventilation valve receives only a short timer signal, when flow rate is high, the timer signal length increases. This ensures that the correct purge air quantity is added in accordance with the intake air quantity.

So, is this a very large volume compared with the volume that is drafted through the 2mm diam orifice from the oil filler that tees into this line on its way the to the intake manifold? What flow volume (crankcase vapors or fuel vapor recovery circuit) dominates this line?

How big is the tube port diameter on the throttle body where this guy ties in?

Leon Speed

The ID is very small. Without actually measuring I would estimate it at appr. 2 mm. So I would guess flow is about the same as through the oil filler neck port. The ID on the throttle body is about 5 to 8 mm I'd guess.

Crank case pressure might be of influence but there are more vents to relieve this pressure. Furthermore the charcoal canister always sees 1atmosphere because of the permanent vent to air.

Why would you want to know?

Tim968

I am working through the concept of putting in Positive Crankcase Ventilation, opening up the valve cover events and oil filter vent. There is an adjustable PCV valve recently added to the market, and I am working through the idea of integrating the Provent inlet to include the valve covers and oil filler neck, and sending the cleaned/filtered air back to the intake manifold via this circuit (part-throttle) and alternatively via check valve to the existing venturi inducer 928 110 690 01 when throttle opening is large and manifold vacuum is low.

Alternatively one could send the Provent cleaned/filtered air to the passenger side of the intake manifold, through a sealed bulkhead fitting like the existing power brake booster connection.

Still a thought exercise at this point.

Tim968

opening up the valve cover events and oil filter vent should have read " opening up the valve cover vents and oil filler vent ( Dragon speak doesn't like me today)

GlenL

Classic PCV has vent to let air into the engine. That's what you're planning? Why?

Leon Speed

I did the latter route.

Tim968

My 928 has the early GTS crankcase vent design, with no venting on DS cam cover, restricted air inlet vent at rear of PS cam cover, and normal size vent at front of PS cam cover, tied in at top right of oil filler via ~10mm hole. I like both Herman K's design and Greg R's design, just weighing alternative approaches to my needs.