I have a couple of spare MAP sensors already hooked up but unused on my car. If one day I buy a spare rubber plug for the timing cover, then I can connect up a spare MAP sensor through there. I can also put one into the airbox. Then we can see the pressure in the crankcase, the airbox and in the manifold when the car is started, as it warms up and how they move about during a test drive.
kind regards
Marek
Just for fun I have re-plumbed the fresh-air source, to the clean side of “A” bank air cleaner. Where the extra air valve used to live. Now if there is excessive blow-by it will wind up in “A” air cleaner. (Or “B” air cleaner, by displacing magnet.) We shall see. No trace of blow-by anywhere so far.
Then you aren’t going over 100mph! 
As you are the only person showing any positive interest in this PCV adventure, I thought I would go over the final version with you.
The only change made to the existing PCV is to remove “B” bank air cleaner and put a fridge magnet over the port you can see. Now the engine HAS to try to pull air from the crankcase.
You will need some 3/8 tubing and two barbed 90 degree elbows. A new timing cover plug with a 3/8 drill bit run through it will give a good tight fit for the first elbow. I ran my tubing vertically beside the coolant fill tube to another elbow, and then a right turn towards “A” bank air cleaner. I was able to put a 90 degree fitting in the back part of the “A” air cleaner, as the final photo will show.
If there is blowby, it will go to “A” air cleaner, not “B” . The system is totally contained, and environmentally friendly, and it works!
If the pressure inside the A aircleaner is the same as the pressure inside the B aircleaner and the pressure inside crankcase is the same at the plug as it is at the B cam cover, then is all you have done is delete the PCV valve?
kind regards
Marek
Marek, nothing has been “deleted”. Jaguar’s PCV design has simply been modified so that the routing of the air to the PCV valve no longer comes from “B” bank. Instead, it is pulled through the crankcase, and then through the oil separator, from the extra plumbing installed in the timing cover plug, (the air intake) which is connected to the air cleaner on the “A” bank side. Self-contained to catch any blow-by as before.
It works. Tested , per Greg’s specifications, to at least 100 MPH.
Hey Dave, still here. A fairly simple test that would be very interesting is. Replace your upper brass 90 with a tee. Connect a length of hose to this extra port and then to vacuum / pressure gauge and place under your windshield wiper so you log readings while driving. This will show what happens at different rpm ranges.
OK, let me see if I understand things correctly.
On the original system (arrows indicates air flow):
On idle/part throttle the engine sees vacuum through:
Crankcase breather → PCV valve → Balance pipe → Inlet manifolds.
On WOT engine sees vacuum through:
Crankcase breather → Opening behind the air filter at B-bank.
So, at least in theory, in both cases there is some negative pressure inside the engine.
So, you closed the port that provides some negative pressure at WOT (created by the restriction of the air filter) at the B-bank air filter housing.
You substituted this by connecting the A-bank air filter housing (behind the air filter) to the inlet at the Chain tensioner plug.
Correct?
At idle you would have:
A-bank air filter housing → Tensioner plug inlet → Engine → Crankcase breather → PCV valve → Balance pipe → Inlet manifolds
So inside the engine you have air circulation instead of pure vacuum.
At WOT:
Tensioner plug outlet → A-bank air filter housing.
What I see is that the tensioner plug serves as inlet at idle/part throttle and as outlet at WOT.
So there must be a transition point when the PCV negative pressure and the Air filter housing negative pressure are the same, so air circulation stops and there is only vacuum from that point on.
Looks like that at WOT the system works pretty much as before, only difference is the engine output tube location (chain tensioner plug) and the absence of the screen filter/oil separator.
As I am not familiar with highlighting various paragraphs posted , this may take some time.
So, Correct? Yes.
“At idle you would have” Mostly correct, but I don’t see how any vacuum could be created at idle, or cruise, for that matter, considering the open chamber at the back of “B” air cleaner. Air circulation? Yes. Pure vacuum? Unlikely, at idle or cruise.
“So at least in theory, in both cases there is some negative pressure inside the engine”? Totally disagree.
Your last two paragraphs are accurate.
My objective in all of this was to get some fresh air moving through the crankcase. As long as there is some vacuum in my intake manifolds, that will take place.
WOT is a lesser concern for me. My “B” air cleaner has remained clean over several thousand miles, and I don’t expect to see oil to suddenly start to appear in my “A” bank air cleaner. If that should happen I will put a filter/screen in the intake/exhaust line from “A” bank.
Hope that addresses your concerns.
Finally- the changes I make to my car might not suit everybody YMMV!
In “The Book” the PCV system is mentioned. Interesting reading.
Cool, now I know I’ve understood the complete system and your modification.
I guess that’s easy to check.
Did you see any difference on idle rpm when you blanked the chamber?
Even if they are not, it’s always very interesting to see them David, and thanks for taking the time to share them.
All the best.
“Difference in idle RPM when chamber is blanked?”
Once the whole system was finished I could not see any difference -BUT when I cover the hole to my fitting on the back of “A” bank air cleaner, the RPM slows down noticeably. I suppose some air could enter the crankcase through the two-piece oil dipstick tube, though, which is not air-tight. I really don’t want to bother with that!
I agree, but with one small edit… instead of “On WOT”, I would say “At any heavy engine load, when there is insufficient vacuum in the manifold to pull the pcv valve open…”.
(I say that because WOT only means “100% open throttle” at redline rpm. At half redline rpm, WOT equals roughly half open throttle and at idle rpm, WOT is achieved at ~35% or less open. This is because at low rpm, the engine already gets all of the air it can use at a partially open throttle. You only need the maximum amount of air (as provided by true 100% pedal to the metal WOT when you are at max rpm.)
I also think that the air pressure at the airbox connection is always going to be lower than that of atmosphere, sometimes not by much, so this will explain why Dave’s hose remains clean. Logic says the blowby, if present, would thus mostly rather still go to the airbox than out to atmosphere. It’s not a measure of “success”, but simply one of less efficacy.
As I see it, all that is going on with the new setup is rather than evacuate the crankcase fully, air is pulled into the crankcase via the new hose in addition to any that was pulled through the crankcase anyway. The total amount of air pulled in at idle is the same, because the idle speed hasn’t changed. Effectively, all that has been done here is that the crankcase is evacuated less, which is why less oil is pulled through. You have simply made the pcv system less strong.
I also think from the way it is being described, that it is not obvious that t is understood that significant vacuum is generated at idle and at cruise. Plenty of manifold vacuum is generated at any time when the engine is not heavily loaded. Driving “at 100mph” is a red herring because maintaining a steady 100mph isn’t necessarily heavy loading. Accelerating hard and going steep uphill are situations when the engine is heavily loaded, i.e. no vacuum generated. This is such a powerful engine that it spends very little time heavily loaded and thus it is generating vacuum (and evacuating the crankcase) a lot of the time.
I reckon you could achieve the same (detune the amount of crankcase evacuation) simply by restricting the orifice size between the pcv valve and the manifold or between the Bbank and the path to the pcv valve. That’s how Jaguar did it on the carburettored v12 cars and on the 6litre models.
The abundance of oil in the Bbank manifold is a measure of the success of the pcv system, rather than a sign of its failure and the modification that I’d suggest is to simply have a catch can inserted between the extraction at the Bbank cam cover and the pcv valve. This would give you maximum crankcase evacuation (and thus fewest leaks through the seals) but stop oil from reaching the Bbank airbox.
Put bluntly, the problem Dave is fixing is a Jaguar design fault that the pipe from the Bbank collects oil in it because it sits there through gravity when the manifold vacuum is not high enough to pull it through the pcv valve into the manifold - it has no choice but to then drain into the Bbank because that is lower down and it won’t flow back uphill once extracted! The way this oil puddling problem is being solved is to have less crankcase evacuation, rather than to fit a catch can somewhere between the Bbank cam cover and the Bbank air cleaner.
The 6litre cars solved this design flaw by taking their evacuation from the jackshaft cover, passing through a huge gauze mesh (much bigger than the little Bbank metal cone) and then making the oil path go upwards a long way (i.e a sort of gravity catch can) with vacuum provided by two broad pipes (with restrictors in them for tuning) to the undersides of the 6litre badged manifolds. The jackshaft cavity (left empty because of the coilpack ignition now replaced the distributor) was stuffed full of metal gauze and any oil which got through that drained back into the centre V. That got you full crankcase evacuation without too much oil getting all of the way to the manifolds.
The fix presented will have more likelihood of oil leaks out of the engine block than either of the two others put forward.
kind regards
Marek
P.C.V. Positive crankcase Ventilation. I have not seen anything positive about Jaguar’s design, nor is there any “ventilation”. The engine could have 20 ins/HG applied to the crankcase, and unless there is some way for air to enter the crankcase, there cannot be any ventilation.
I really do not agree with much of your presentation, but I respect your right to present it.
As for my engine leaking oil- it does not leak now, and I do not expect it to in the future.
I think I will now leave this topic.
Cheers, Dave.
Just wondereing. Engine vacuum (from inlet manifold) is also used fo actuate the bellows of the cruise control. Doesn’t this mean that there is always some vacuum? Cruise control is not failing when you drive uphill/at other high load, right?
I was also wondering about this terminology…!
The Cruise Control never goes to WOT, but if it did I guess it would be a point that it would not have enough vacuum to operate.
Nevertheless, even at full WOT there will always be some amount of vacuum in the manifolds due to friction and the restriction of the air filters, albeit very small/close to zero.
This is the reason that the brake servo and climate control vacuum inputs have check valves.
Don’t be cross Dave, we like you and we like to see what you have done.
We all experiment and try to improve things, sometimes successfully, sometimes not, but in the end mechanics and physics will have the last say. As Richard Feynman said, you can’t fool nature.
I know that all modern engines provide ventilation, and the Jaguar V12 does not, so I can very well see your point. It’s also a very elegant solution for the problematic chain tensioner plug.
On the other hand Marek also has a point, you substituted Vacuum with Airflow.
But the V12 has a rope crankshaft seal that relies on vacuum to keep the oil in, and not to mention a general predisposition by design to leak oil.
This would be my one and only concern.
There is lots of vacuum, almost all of the time.
Here is an Excel table summary from a one hour drive down windy B roads taken last month.
The cruise control probably tries to maintain its pressure setting via a one way valve in its path which gets vented to air when you want to turn the cruise control off. That’s probably what the bellows are for - pressure and volume are exactly inversely correlated.
As for ventilation, what Jaguar had was a two stage crankcase evacuation mechanism:-
1/ at moderate to high vacuum (i.e. low to medium engine loads), the crankcase was subjected to vacuum because the manifold vacuum pulled the pcv valve spring open. This will have attempted to draw out vapours from the crankcase into the manifold.
2/ When manifold vacuum was not strong enough to pull the pcv spring open, the crankcase was now at the same air pressure as the Bbank airbox, i.e. a much poorer vacuum source. Any oil between the Bbank cam cover and the airbox now just pooled in the pipe and slowly drained into the airbox. Not a fantastic design.
What Dave has done is go directly to the second stage but also make that even weaker, by deliberately admitting air into the crankcase. Instead of the engine air coming from the two inlet trumpets, now a bit less air comes through the inlet trumpet because a bit has been pulled through the crankcase instead.
So what does the pcv valve do now? If it is just left connected to the airbox, then it simply provides a spring controlled bleed of air when manifold vacuum is high. I don’t see much point in that.
If the crankcase is kept under (some) vacuum by the manifold, then any air that can get in via the dipstick tube, the rear main seal or any gap it can find, will get in and then by pulled into the manifold. This means leaks will tend to come into the engine, rather than out of the engine.
I’m sorry Dave feels offended, but he is no longer evacuating the crankcase. Crankcase evacuation has been replaced with crankcase ventilation.
kind regards
Marek
The problem would be when it would want to accelerate, then the bellows would be connected directly to the manifold.
I agree that the vacuum will be much weaker, but that doesn’t render the PCV valve useless.
At idle the manifold has 15-18 inHg of vacuum.
The opening at Dave’s A-bank filter box has a tiny bit less than atmospheric pressure.
Air will go in and the PCV valve will moderate the flow same as before.
I think this was the exact logic behind, the inappropriately named, Jaguar’s PCV design.
