Does the AJP include a PCV valve?
Discussion
There's no valve as such, just an open breather from the crank case that vents into an oil catch tank under the off side air box. The catch tank has a gause in it so that (in theory) the liquid collects and drains back into the engine whilst the vapours get sucked into the off side cylinder bank to be combusted. The reality is that the catch tank either leaks externally or fills with oil letting too much oil into the inlet.
its effectively using vacuum from the induction to relieve pressure in the crankcase. (positive Crankcase ventilation) i have been p!ssing about with mine, as on track days she was puking oil out the breathers. One standard breather is not enough for sustained high revs. I think i have cracked it now though. Similar thread running here already.
From what I've read, the PCV value reduces flow at idle when inlet manifold vaccum is high and oil mist low and increases it when as revs rise when manifold vacuum is low and oil mist high. Does this mean most cars vent their crankcase into the inlet manifold after the butterfly rather than into the air box. Is that why the AJP does not have one.
I only ask because the plugs on the offside bank seem more fouled than the nearside and I was windering if it was oil.
I only ask because the plugs on the offside bank seem more fouled than the nearside and I was windering if it was oil.
jonbarrett said:
From what I've read, the PCV value reduces flow at idle when inlet manifold vaccum is high and oil mist low and increases it when as revs rise when manifold vacuum is low and oil mist high. Does this mean most cars vent their crankcase into the inlet manifold after the butterfly rather than into the air box. Is that why the AJP does not have one.
I only ask because the plugs on the offside bank seem more fouled than the nearside and I was windering if it was oil.
Yes after the butterfly, i only have one. So it is alot easier to do. I am also putting a catch tank in this line, there are special baffled ones for this job, it also has to be sealed as it has to pull vacuum for the system to work. I only ask because the plugs on the offside bank seem more fouled than the nearside and I was windering if it was oil.
Edited by Brummmie on Wednesday 25th March 08:54
Edited by Brummmie on Wednesday 25th March 08:56
I may be wrong, but as I understand it the small pipe that attached to the catch tank goes to the 4- way connector in the middle of the v, which in turn runs back to the carbon cannister. I would imagine then that this smaller pipe is there to let the engine combust the vapours produced when the carbon can purges itself.
brogenville said:
I may be wrong, but as I understand it the small pipe that attached to the catch tank goes to the 4- way connector in the middle of the v, which in turn runs back to the carbon cannister. I would imagine then that this smaller pipe is there to let the engine combust the vapours produced when the carbon can purges itself.
My understanding was that the small pipe runs to a pressure sensor near or in the ECU...as does the small pipe from the near side air box...not sure what the ECU does with this 'information' though...? presumably it alters the fuel air mix? or maybe its monitoring / sampling the air temp in the air box...?I'm running a filter / catch tank arrangement that is vented to atomsphere...car doesnt use any oil...my understanding is that the vent is there to aleviate excessive pressure in the crankcase...the only reason the vent discharges into the off side air box is because its the closer of the two airboxs (closer to the vent outlet pipe that is) so that any discharge (urgh...), be it oil vapour or actual oil itself, is burned off...in other words it has nothing to do with the vacuum pressure in the air box...?
Could be wrong...any thoughts?
The small pipe from the nearside airbox goes through the bulkhead to the ECU where it measures air pressure.though displayed when connected to the PC the standard software doesnt use it for engine management.
The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.
rgds Peter
The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.
rgds Peter
V8CER said:
The small pipe from the nearside airbox goes through the bulkhead to the ECU where it measures air pressure.though displayed when connected to the PC the standard software doesnt use it for engine management.
The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.
rgds Peter
''The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.''The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.
rgds Peter
Really...so if the standard crank case breather assembly is removed from the underside of the air box (replaced by a breather and oil catch tank) there is no need for the small rubber pipe...? It could just be blocked of...? I was under the impresion it was for measuring the pressure in the offside air box...?
peteA said:
V8CER said:
The small pipe from the nearside airbox goes through the bulkhead to the ECU where it measures air pressure.though displayed when connected to the PC the standard software doesnt use it for engine management.
The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.
rgds Peter
''The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.''The pipe from the 4 way connector goes rearwards to the carbon cannistor and is called the 'purge' pipe both this and the smaller pipe from the oil breather feed to the 4 way connector and are consumed through both throttle bodies 'after' the butterfly.
rgds Peter
Really...so if the standard crank case breather assembly is removed from the underside of the air box (replaced by a breather and oil catch tank) there is no need for the small rubber pipe...? It could just be blocked of...? I was under the impresion it was for measuring the pressure in the offside air box...?
I did some investigation a while ago - the thread is here
OK, so the pipes coming off the fourway connector go to: the carbon canister, both inlet manifolds after the butterfly and the offside airbox/oil catch can.
At idle, the manifoilds are at maximum vacuum, sucking air down the tubes from the carbon canister (provided the purge valve is open) and the air box.
Why connect the airbox to a vacuum at that point? Is it to draw the crankcase gasses into the manifold after the butterfly at idle.
At idle, the manifoilds are at maximum vacuum, sucking air down the tubes from the carbon canister (provided the purge valve is open) and the air box.
Why connect the airbox to a vacuum at that point? Is it to draw the crankcase gasses into the manifold after the butterfly at idle.
I wouldn't worry about this stuff too much, its all geared around crude emissions control. I've removed the carbon cannister (fuel tank vents to atmosphere via one-way rollover valve and filter) and blocked off both manifold tapping points.
A PCV valve is associated with a recirculating crankcase breather which the Cerbera doesn't have as standard. It's effectively a one way valve, and amongst other things acts as a flame trap to prevent a backfire igniting combustable gases within the crankcase.
Although a vacuum (as generated behind the butterflies at idle) would be good for extracting crankcase gases (as in the small pipe on the stock setup on the AJP8 Cerbera), it serves little other purpose than to reduce emmissions by way of burning the noxious crankcase gases (blowby and oil mist), largely at idle only. The problem I've found with the Cerbs standard breather is during sustained high rpm driving such as on say the autobahn, or on a trackday. Another thread is running with reference to that. Basically during these conditions, all of the crankcase blowby (much much greater volume than at low rpm) is fed directly into the offside intake. Many people have experienced (going back years and years) oil dripping out the airbox, oil dripping onto the offside manifolds and as someone has mentioned in this thread, spark plugs on the offside bank being more sooty.
A PCV valve is associated with a recirculating crankcase breather which the Cerbera doesn't have as standard. It's effectively a one way valve, and amongst other things acts as a flame trap to prevent a backfire igniting combustable gases within the crankcase.
Although a vacuum (as generated behind the butterflies at idle) would be good for extracting crankcase gases (as in the small pipe on the stock setup on the AJP8 Cerbera), it serves little other purpose than to reduce emmissions by way of burning the noxious crankcase gases (blowby and oil mist), largely at idle only. The problem I've found with the Cerbs standard breather is during sustained high rpm driving such as on say the autobahn, or on a trackday. Another thread is running with reference to that. Basically during these conditions, all of the crankcase blowby (much much greater volume than at low rpm) is fed directly into the offside intake. Many people have experienced (going back years and years) oil dripping out the airbox, oil dripping onto the offside manifolds and as someone has mentioned in this thread, spark plugs on the offside bank being more sooty.
Edited by longbow on Thursday 26th March 07:43
brogenville said:
There's no valve as such, just an open breather from the crank case that vents into an oil catch tank under the off side air box. The catch tank has a gause in it so that (in theory) the liquid collects and drains back into the engine whilst the vapours get sucked into the off side cylinder bank to be combusted. The reality is that the catch tank either leaks externally or fills with oil letting too much oil into the inlet.
Has anyone managed to improve on the standard catch tank, because it seems undersized for what it is supposed to do. I would totally agree with your real world description, it definitely does leak, but perhaps that is more a symptom rather than the underlying problem.ukkid35 said:
brogenville said:
There's no valve as such, just an open breather from the crank case that vents into an oil catch tank under the off side air box. The catch tank has a gause in it so that (in theory) the liquid collects and drains back into the engine whilst the vapours get sucked into the off side cylinder bank to be combusted. The reality is that the catch tank either leaks externally or fills with oil letting too much oil into the inlet.
Has anyone managed to improve on the standard catch tank, because it seems undersized for what it is supposed to do. I would totally agree with your real world description, it definitely does leak, but perhaps that is more a symptom rather than the underlying problem.It really is one of those cases of "they all do that sir".
gruffalo said:
It really is one of those cases of "they all do that sir".
Yes, I'm sure you're right.But the thing is, I reckon the lack of PCV valve (and the excessive blow by) is in part responsible for my continuing pinking issues.
Since this only happens at low revs (and therefore high vacuum) I've been wondering whether the absence of PCV valve is messing up the mixture and causing the pinking.
The smoking gun as it were, is the oily plug on the cylinder that suffered head gasket failure - which is the cylinder RIGHT NEXT TO the crank case breather/catch tank - I can't believe that's just by chance.
pic courtesy of SteveStrange007 who's had a pair of airboxes for sale on eBay for as long as I can remember
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