Breather Question?

[Chris Wilson]

If the engine, unlike, say a GTR or GTS-t Skyline RB2*DET lump, does not push oil out of the cam box breather(s) due to excess oil in the top end or excess blowby, it's a good thing, from the point of view of less oil contamination, or intake charge contamination, to vent to atmo, probably via a catch can. The ONLY reason a PCV valve and vent to intake system is used is to reduce emissions. It contaminates the sump oil and adds water content, unecessarily. It reduces det resistance by lowering effective ocatne due to oil contamination of the intake charge. I always vent my own engines to atmo.

 

A true race engine, with a dry sump system with BIG scavenge pumps, can create a high vac inside the engine, even at high loads and RPMS. In these very specialised cases the venting is done totally differently. The vac is used to aid ring seal at mega rpms (over 10,000). It doesn't apply to road car, wet sump engines.

 

If I were running a 2JZ-GTE engine I'd block off the PCV valve port at the intake side, remove the valve, and vent the engine to atmo via a catch can. In the case of the RB2*DET engines in Skylines, run on a race track, a lot more needs doing, as they pump oil into the top of the engine faster than it can drain back, as a result of very poor drain area in the head and excessive crank pressures, as the block isn't very good at stopping blow by at high cylinder pressures. I had to go to extreme lengths to cure this on my R33 GTS-t, which cost a packet in materials and development time, but it's now sorted!

 

HTH.

[Tricky-Ricky]

If the engine, unlike, say a GTR or GTS-t Skyline RB2*DET lump, does not push oil out of the cam box breather(s) due to excess oil in the top end or excess blowby, it's a good thing, from the point of view of less oil contamination, or intake charge contamination, to vent to atmo, probably via a catch can. The ONLY reason a PCV valve and vent to intake system is used is to reduce emissions. It contaminates the sump oil and adds water content, unecessarily. It reduces det resistance by lowering effective ocatne due to oil contamination of the intake charge. I always vent my own engines to atmo.

 

A true race engine, with a dry sump system with BIG scavenge pumps, can create a high vac inside the engine, even at high loads and RPMS. In these very specialised cases the venting is done totally differently. The vac is used to aid ring seal at mega rpms (over 10,000). It doesn't apply to road car, wet sump engines.

 

If I were running a 2JZ-GTE engine I'd block off the PCV valve port at the intake side, remove the valve, and vent the engine to atmo via a catch can. In the case of the RB2*DET engines in Skylines, run on a race track, a lot more needs doing, as they pump oil into the top of the engine faster than it can drain back, as a result of very poor drain area in the head and excessive crank pressures, as the block isn't very good at stopping blow by at high cylinder pressures. I had to go to extreme lengths to cure this on my R33 GTS-t, which cost a packet in materials and development time, but it's now sorted!

 

HTH.

 

 

Sounds like a man who knows what hes talking about! best come and join the stupid club with me! LOL

[Digsy]

If the engine, unlike, say a GTR or GTS-t Skyline RB2*DET lump, does not push oil out of the cam box breather(s) due to excess oil in the top end or excess blowby, it's a good thing, from the point of view of less oil contamination, or intake charge contamination, to vent to atmo, probably via a catch can. The ONLY reason a PCV valve and vent to intake system is used is to reduce emissions. It contaminates the sump oil and adds water content, unecessarily. It reduces det resistance by lowering effective ocatne due to oil contamination of the intake charge. I always vent my own engines to atmo.

 

A true race engine, with a dry sump system with BIG scavenge pumps, can create a high vac inside the engine, even at high loads and RPMS. In these very specialised cases the venting is done totally differently. The vac is used to aid ring seal at mega rpms (over 10,000). It doesn't apply to road car, wet sump engines.

 

If I were running a 2JZ-GTE engine I'd block off the PCV valve port at the intake side, remove the valve, and vent the engine to atmo via a catch can. In the case of the RB2*DET engines in Skylines, run on a race track, a lot more needs doing, as they pump oil into the top of the engine faster than it can drain back, as a result of very poor drain area in the head and excessive crank pressures, as the block isn't very good at stopping blow by at high cylinder pressures. I had to go to extreme lengths to cure this on my R33 GTS-t, which cost a packet in materials and development time, but it's now sorted!

 

HTH.

 

I think this is worthy of a bit more discussion (especially now that CW is involved )

 

Surely its stilll true to say that the Skyline lump isn't a great example of how to or how not to change the breather system for high power is the engine has such poort blow-by and oil hang-up characteristics from stock? If the engine is that poor then no wonder its common to see oil catch tanks with atmospheric breathers attached. Likwise, you could say that a 2JZ running high boost with knackered rings needs to be vented to atmosphere because the blowby will carry over so much entrained oil that it will dilute the intake charge.

 

The common factor here is that something is wrong with the engine, and in either case it is something different. It still doesn't automatically follow that because a lot of Skylines use open catch cans then its the best solution for the Supra as well.

 

We all know that CW comes from a race car background, so catch cans and externally vented breathers are second nature to him. Conversley I come from a road car background so all I usually get to see are closed systems and I know that its perfectly possible to design a breather system that does not need to be vented to atmosphere because even at the worst case the carryed over oil is in the 1-2g per hour region. We wouldn't have cars like the McLaren F1 and the Bugatti Veryon if this wasn't possible.

 

I've said before on here that if your car is carrying over enough oil to warrant using a catch tank then I'd be more concerned about the state of the ring pack than the breather system.

 

With proper oil separation and a decent bottom end to start with I don't see why you couldn't run a closed breather system even on a highly boosted engine,but If I've learned anything at all about oil separation and breathers its that what they need is space and IMHO most of the aftermarket catch cans are way too small to get anything like the amount of oil out of the system to get back to OEM-spec levels of carry-over.

 

I still reckon that most people run catch cans once they get to a certain level of tune because most other cars run catch cans - not because of any great understanding of whether or why they are really necesary. From Chris's post alone it seems like the Skyline and 2JZ engines are very different, and may require similar breather mods but for different reasons.

 

[JohnA]

Race engines get rebuilt often and their blowby is negligible compared to aged and tired overboosted supras.

 

I would never want my sump to be connected straight to atmosphere --- not in a turbocharged engine where there is an additional serious issue of turbocharger lubrication once sump pressure exceeds a minimum (small fraction of a psi usually)

 

A scavenging pump would be better, yes, but who's gonna do this on a road car?

Next best thing is to use the intake vacuum and separate the oily crap in the process.

A good catch tank will provide sudden volume expansion, sudden cooling and a torturous path for the oily mist, forcing the crap to solidify and stay away from lowering our octane.

[Tricky-Ricky]

Digsy and Chris Wilson, my previous posts where based on going back through a lot of old posts regarding engine breathing and i noticed a lot of comments about the amounts of oil that was being ejected through BOVs and observations on the amount of oil found in intake pipework and intercoolers, which lead me to believe rightly or wrongly that A, there are either a lot of worn out Supras out there, B or that there was a breathing problem! so my reasons for daring to suggest a catch tank and possible vent to atmosphere, where based on that, and the fact that i have seen the results of other engines running a closed system, and when venting to atmosphere, and it has been the difference between passing an MOT and not!

The only reason i have now replied now is that you and Chris Wilson seem to be the only people who have made an effort to reply without casting aspersions about peoples intelligents!

[supra matt]

hi tricky how did you get on with this in the end? as im looking to add a catch tank to mine . and would like to no where is best to connect up to ? pics would be nice if any one got some .

[Kranz]

I used to do oil carry over & blowby tests on development engines during durability runs on test beds.

 

If you want to actually measure the amount of oil & blowby out of an engine with different breather systems then let me know & I'll give anyone the heads up on what kit to use (can be done on the cheap).

 

Steve

[Tricky-Ricky]

hi tricky how did you get on with this in the end? as im looking to add a catch tank to mine . and would like to no where is best to connect up to ? pics would be nice if any one got some .

 

Can of worms mate:rolleyes: i presume you have read the preceding pages?

i am currently still experimenting, and at present have a catch tank plumbed into the so called full throttle breather on the exhaust/turbo side which goes back into the intake at the original connections, was open to atmosphere but since blowing the front main seal, i thought it would be prudent to get to the bottom of why the seal went first, (which i still think was down to oil pressure problems rather than blow by) if you want a pic, look for my last engine bay pic, you can see how its done from that, PM me if you need anymore info:)

[Tricky-Ricky]

double post

/vbb/images/smilies/bbcode_oops.gif

[Digsy]

I used to do oil carry over & blowby tests on development engines during durability runs on test beds.

 

If you want to actually measure the amount of oil & blowby out of an engine with different breather systems then let me know & I'll give anyone the heads up on what kit to use (can be done on the cheap).

 

Steve

 

We just use plastic bottles big enough to let the oil drop out. One hose in, one hose out.

 

Bit tricky to get meaningful measurements in a car, though, isn't it? To do anything meaningful you would want to run fixed speed / load points and measure oil carryover for each.

[supra matt]

thanks mate ill be intouch :-)

[Kranz]

We just use plastic bottles big enough to let the oil drop out. One hose in, one hose out.

 

Bit tricky to get meaningful measurements in a car, though, isn't it? To do anything meaningful you would want to run fixed speed / load points and measure oil carryover for each.

 

Yep, thats the only way to do it properly.

 

I used to use the AVL blowby meter and take readings at idle & peak torque.

 

Blowby itself was through 2 glassfibre circular filters (emissions papers for diesel emissions tests particulate measurement) that were in a holder in line with the blowby system. There were switched with pneaumatics so the blowby gasses at peak torque were going through them for 1 minute. Then they were dried in a humidity controlled room and weighed to a high resolution to get the oil carryover in kg/hr.

 

Pretty complicated.

[b_have]

Just seen this, have to say I'm with tricky. I can't see any valid reason for not venting to atmo. I have just increased my hotside breather to half inch pipe exiting near the compressor intake (until I find a suitable catch tank).

Was also considering removing the pcv valve and vent this side similarely.

[Digsy]

Just seen this, have to say I'm with tricky. I can't see any valid reason for not venting to atmo. I have just increased my hotside breather to half inch pipe exiting near the compressor intake (until I find a suitable catch tank).

Was also considering removing the pcv valve and vent this side similarely.

 

Well, in a nutshell, if you route to atmospheric you'll be running your crankcase at a positive pressure, which is bad. If you route to the intake system you'll be running at a negative pressure, whichis what its designed to do and is good.

 

By "bad" and "good" I mean for the life of your oil seals, turbo oil drain, etc. which ultimately means bad for durability.

[b_have]

Well, in a nutshell, if you route to atmospheric you'll be running your crankcase at a positive pressure, which is bad. If you route to the intake system you'll be running at a negative pressure, whichis what its designed to do and is good.

 

By "bad" and "good" I mean for the life of your oil seals, turbo oil drain, etc. which ultimately means bad for durability.

 

So I'm good at the mo Was wondering exactly how much vacuum is created right in front of the compressor?

(I would guess not much with a free flowing filter) Maybe I will leave the plumbing there as seen very little evidence of oil injestion (no smoke at wot/7000+revs) Also the PCV is shut except on over run, so not effecting any blowby issues.

[dandan]

....

[Tricky-Ricky]

Unfortunatly having lower pressure below the rings is a pretty tall order;)

[Digsy]

All IMHO....

 

We all know the idea is to try to have lower pressure beneath the rings than above and minimizing emissions, octane dilution and loading on seal areas. As CW said, certain dry sump setups can be tailored to give the added benefit of some vacuum in the crankcase - obviously does not apply to us. We have to make the best we can with what is either in place or economical to change – maintaining a beneficial pressure differential whenever we can.

 

The purpose of a closed breather system is to maintain a negative pressure in the crankcase. not to maintain any pressure "balance" across the piston rings. The depression in the crankcase wil only be 20 to 50 milliibar at WOT (assuming a stock setup) so in the induction stroke at part throttle the pressure above the rings will certainly be lower than that below.

 

For me, optimization of the breather system is for the purpose of removing any possible chance for octane dilution, and minimizing crankcase pressure under the most damaging conditions for the seals.

 

Fair enough. as far as I am aware no-one has really ever quantified the octane benefits of running open versus closed breathers. Ian C has just changed his 600+ big single from an open WOT breather to a closed one so maybe he'd be a good one to comment. Many people, on the other hand have blown out crank seals due to running a positive crankcase pressure.

 

Max blowby (worn rings blah blah, put to one side) will occur under boost.

 

Not necessarily. A newly run-in ring set will tend to seal better when under load. However, as the revs rise, the sealing gets progressively worse. The worst case for ring sealing is actually max speed / low load.

 

Ring blowby in this instance will put crankcase pressure higher than atmospheric - venting to atmosphere therefore, is not a problem.

 

Think about what you've written here. The problem is not the gases finding their way out of the engine, its whether they create a pressure rise in the crankcase. Just because the crankcase is connected to atmospere doesn't mean it will be at atmospheric pressure. Starting with a crankcase at atmospheric pressure and then allowing blowby gases to enter it will create a positve pressure, whereas starting with a crankcase below atmospheric and then adding blowby gases will (hopefully) still leave you with a crankcase below atmosperic prressure.

 

The pressure differential is in our favour. In this instance the stock system is feeding oil laden vapour into the turbo intake – not something I’d wish to do (for the sake of keeping the intake system oil mist free).

 

Breathers do carry oil vapour (and water vapour and other constituents) 'tis true, but if the engine is on good nick the rate should be in the order or 1g maybe 2g per hour. That's not a lot of oil. As I've said many time son here, if you are carrying over enough oil to make you worried about diluting yout intake charge then you have a bigger problem with ring sealing. Don't malign the breather system - its not the root cause of the problem.

 

On the overrun or at idle, chamber pressure will be lower than atmospheric. Vapours from the crankcase can be drawn past the rings into the chamber. The pcv’d connection to the intake attempts to balance the pressure above and below the rings minimizing the vacuum pumping of oil into the chamber, minimizing over run emissions.

 

Not quite. The PCV is only there to ensure that you don't pull too much of a vacuum into the crankcase at part throttle. Too much vacuum is just as bad as too much prressure. The excess vacuum is balanced by reverse flow through the WOT breather.

 

I intend to run a large breather hose from both cam covers to a breather box/catch can, minimizing backpressure in the breather system and reducing crankcase pressure to as close to atmospheric as possible (under boost). Under boost this should hopefully function with less restriction than the stock system.

 

Even if you reuce the restriction in the external parts of your breather system to zero, the blowby gases still have to make their way up from the crankcase through the internal galleries. It will still build up a positive pressure in there. Maybe not as much, but still some.

 

I may run a pcv type connection to the intake to keep some sort of pressure balance on the overrun. However, some sort of filtration will be needed on the catch tank vent to prevent dust/crud being drawn into the catch tanks (and arguably into the intake). This is the main reason for the location of the exh cam breather vent - nicely filtered already.

 

All true, but in a closed system any air flowing into the engine through the WOT circuit on the overrun has already passed through the stock filter

 

For me, saying that.. “Toyota did it that way, so why mess with it” is not a good reason to leave the stock system in place if it can be improved. People don’t keep the seq twins, the cats or stock exhaust “just because Totota spent £xxxxx developing those areas”

 

Very true, but I think the closed breather system has got a really bad name for no good reason. Adding a catch tank or venting to atmosphere seems to be one of those things that people do simply because lots of other people do. As I said above, adding a catch can or venting to atmosphere to stop the oil getting into your intake is treating the symptom, not the disease. Don't forget that all mass-production high powered cars right up to the Bugatti Veryon will have a closed breather system.

 

Just my 2p worth, not trying to tread on any toes.

 

No probs Out of interest, have you read my breather system writeup in the downloads section?

[dandan]

I have.