Head Breather Pipe Investigations

[Thuppu]

Many set the crankcase ventilation system to atmosphere. But aren't you supposed to suck out the blow-by using vacuum?
If you route it to atmosphere, there is no more vacuum.

So is there any difference using vacuum or vent to atmosphere? Is there some reason that the vacuum suck is better?

[andy10v]

Any suggestions for a reasonably priced seperator pot?

[Acidburn]

Any updates to this?

[gnutz2]

So is there any difference using vacuum or vent to atmosphere? Is there some reason that the vacuum suck is better?

Yes vacum is great in the crankcase, the bigger the pressure difference between the combustion chamber and the crankcase the harder the piston rings are pressed out, the better the seal.

The rings also pass a lot of heat from the piston crown into the cylinders and water jacket so your killing two birds with one stone.

Now imagine on a high boost high horsepower car, small breathers and a lot of blow-by could get out of hand and easily get bogged down with high crankcase pressure if not thought through properly.

Thats how i see it

Also throw in a good bit of oil surge into the sump and it's a wonder any oil maneges to stay in the there

[4WheelDrifter]

Less pressure in the crankcase reduces windage losses. Think of the air under the pistons resisting the downward stroke, as it has to move to another place in the crankcase.

Less pressure = less loss = more power to the crank.

The problem is you don't want oil vapour in your intake, as oil doesn't burn as well as petrol and increases the likelihood of detonation.

So really you want plenty of suck-age from the intake, but without sucking up oil vapour. So that's why a cyclone/oil separator is a good solution, without going as far as a dry sump system.

[Thuppu]

Hmm, the orginal block breather is quite small so maybe the vacuum is needed. But if you upgrade the breathing..? I'm gona try to do a couple of extra breathers on the camcover like BlackS2 has done here: http://www.s2forum.com/forum/showthr...t=47923&page=3 I already buyed a second camcover I can use for the mod and order some AN12 alu weld bungs and 90degree fittings. Had also to made the oil separator/catchtank... The idea is to draw two 15mm hoses from the camcover and one 19mm hose from the block, to the tank. The tank is breathing to atmosphere thru a filter, but the oil is returning to the sump. How do this sound?

[newsh]

Nice work Rusty
Another thing worth thinking about, if you get crankcase pressure during high boost (and right hand cornering) then the oil is just as likely to come up the drain-to-sump as it is to come up the block breather pipe so a suitable one way valve would be a good idea.

For the cam cover, I wonder if there's a way of making a spacer to go under the filler cap with a take off? A K24R product perhaps?

[Rusty]

As long as the drain to sump remains below the oil level then you're fine. IMO, the oil is forced up the pipe due to the flow of air from teh breather system to the inlet / catch tank. The amount of oil that I collected on track is only slightly more than the oil that was leaving the head under hard acceleration (admittedly in lower gears) so treating each problem equally should solve the problem 99%.

I will be fitting a swirl pot and some 30mm pipe, this will be more than adequate to prevent the oil from the head entering the air stream and will be combined with a catch tank for double protection.

On a 3B, where space is tight, I'd suggest that a suitable swirl pot will be ample in many cases, perhaps yours being the exception there John, just feed the swirl pot output into your current catch tank, it shouldn't have much to do once the SP is installed.

[Rusty]

Vacuum created at the inlet boot under full boost isn't that large and as that's the only source of vacuum under load (i.e. plenum is greater than atmosphere) it's worth using but not really that big an effect. Better to retain the sealed system from a fumes point of view IMO.

Under idle conditions the plenum can be used but your system has to be sealed to ensure that there isn't an air leak and also retain the one-way valve (that's still working) to prevent the oil breather becoming pressurised, oh, and there's hardly much blow by or losses at idle anyway and if you're dragging oil into the cylinders due to high vacuum, then that sort of defeats the point of having a catch tank setup in the first place. The PCV valve prevents too much scavenging of the vented gases at idle and means that fresh air is drawn from the inlet boot.

[Rusty]

Speaking with a friend who worked at Landrove/Jaguar on cooling and crank case ventillation, you're looking at between 50 and 100mBar vacuum due to the flow of air at full chat. I would need to confirm this with testing. Obviously much less than the 0.6 Bar in the plenum under idle.

[JP]

Totally forgot about this post, get sidetracked too easy when doing too many things

Will sort a sketch out today. Can confirm that my current setup all I drain out of the catch tank every 3-4mnths is coloured water moisture no oil at all. The condition of the oil is as I would expect on a mildly driven car on the 5000mile oil change that I do (approx 4 times per year). Likewise I rarely pop the bonnet to check oil levels now thanks to the return to sump.

[JP]

OK bit of a sketchy diagram but hopefully makes sense without drawing the engine in there.

First of I disconnected the crankcase to Intake Manifold but left the evap canister connected.

Next I took the fire trap and all the original plumbing from the crankcase junction box and binned it as this lot replaces it.

In the case of my car I wanted a little extra so I routed the back of the rocker cover to it's original location at the crankcase junction box and made an extra outlet from the rocker cover to the oil separator.

You can eliminate the need for the extra outlet and just route the back of the rocker cover direct to the oil separator. I took the approach of the extra outlet as I'm a belts and braces type of character and can weld.

Other than that the connections are as the dodgy picy shows. I know it works 100% as the catch tank only catches oil coloured water, my oil is good condition when changed, my boost pipes are dry and my oil consumption is next to nil.

I'm not sure how much more basic I can make it before it becomes un effective because as it is working I'm unwilling to try. However in theory if you eliminate the catch tank you will get the water vapour it is collecting back into your intake but still no oil as it isn't collecting any. As to how saturated the pipes then become is difficult to tell without trying it but like people say if it aint broke don't fix it.

[Rusty]

My design uses a large bore pipe to allow plenty of airflow at a slower speed, as well as allowing the excess oil to drain back.

Going from 19mm to 30mm pipework increases XSA by 250% and so slows the air by 2.5 times, the ID or 63.5" for the swirl pot means the XSA increases 11 fold! Overall, this should work to a decent % of JP's system but without the complexity of adding a sump return. More for occasional track use then.

Just thinking about it, I'd be as well sorting out a head breather that runs from the filler cap as the head breather seems to be what's overwhelming the system and the swirl pot is an attempt to deal with that...

[Thuppu]

Here is one quite nice diy catch can/separator build: http://bbs.scoobynet.com/projects-40...catch-can.html

[JP]

^^^^ that's just a very extravagant catch tank with filtration. An oil separator is much more simplistic than that but only works if it has a drain back for the oil it separates.