Discussion
The 'God damn shunt' topic highlighted the problem of the full vacuum leak to atmosphere via the tee'd connection from the plenum to the crankcase ventilation pipe. However the suggested positioning of the valve, at the firetrap, didn't address that particular problem. And I'm struggling to see any point in the valve at the firetrap position.
As I understand it, some form of positive crankcase is a good thing. The thick pipe between the firetrap and the throttle body will always provide crankcase ventilation but it will only be positive ventilation under certain conditions. The tee'd connection into the plenum provides the positive aspect under the remaining conditions, that is at small throttle openings. The only problem, therefore, with the existing system is that the vacuum connection is uncontrolled and this is then should be where the PCV valve is required.
I bought one of the suggested valves as shown.
It appears to work by restricting flow as vacuum applied to the silver end increases. So the silver end faces the plenum.
So this is how I fitted it between the main pipe and the plenum and using some pieces of hoses of various diameters to provide a socket for the valve and a connection to the plenum.
Or have I got it all wrong???
As I understand it, some form of positive crankcase is a good thing. The thick pipe between the firetrap and the throttle body will always provide crankcase ventilation but it will only be positive ventilation under certain conditions. The tee'd connection into the plenum provides the positive aspect under the remaining conditions, that is at small throttle openings. The only problem, therefore, with the existing system is that the vacuum connection is uncontrolled and this is then should be where the PCV valve is required.
I bought one of the suggested valves as shown.
It appears to work by restricting flow as vacuum applied to the silver end increases. So the silver end faces the plenum.
So this is how I fitted it between the main pipe and the plenum and using some pieces of hoses of various diameters to provide a socket for the valve and a connection to the plenum.
Or have I got it all wrong???
Looks like I got it wrong anyway and I have the valve the wrong way around, clearly my suck isn't as strong as idle vacuum suck! I'll reverse it in the morning.
The google description:
The restricted hole is 3.3mm which I suppose gives a compromise of too much flow at idle and not enough under load?
The google description:
The restricted hole is 3.3mm which I suppose gives a compromise of too much flow at idle and not enough under load?
So looking at that diagram, the 'mushroom' on the n/s rocker cover does the same job as the pipe from air filter to filler cap ie admits filtered air. Then the hose from the fire trap on the o/s rocker cover should go direct to the plenum via the pcv valve and the connection to the throttle body removed.
The PCV valve is then doing the job of the plenum/small orifice vacuum ventilation at low load and the throttle body/large hose/venturi effect ventilation at high load?
The PCV valve is then doing the job of the plenum/small orifice vacuum ventilation at low load and the throttle body/large hose/venturi effect ventilation at high load?
ChimpOnGas said:
At WOT there is no vacuum, this is why venturi vacuum at the throttle body is used!
There must be some surely! I'll have a look at the Megasquirt logs from my Lotus to check, but I can't recall MAP getting that low and it's only getting vacuum from ITB's.I thought that there was insufficient vacuum at WOT due to the restrictor used to control closed throttle vacuum, and that was why the venturi vacuum was used. The PCV is an automatically adjusting restrictor.
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