View Full Version : The perfect PCV solution?
Guys,
For those of you who aren't members there has been this mega-thread raging on supraforums about PCV's (http://www.supraforums.com/forum/showthread.php?s=&postid=2043064#post2043064). Now, I'm interested because I'm just about to fit an HKS SSQV and I've been warned that the oil from the stock PCV will blx up my new BOV.
The arguement seems to be:
On the one hand, Positive Crankcase Ventilation helps your piston rings seal and, therfore, makes power and increases the longevity of your motor. So you have to have a sealed system with a vacuum source.
On the other hand, nothing could be more EVIL (that's an Austin Powers' EEEVIL) than pumping hot, oil vapour laden, gas into your throttle body, and worse, your air intake.
Has anyone come up with a sealed system which doesn't pump oil into your intake, your IC, your BOV and your turbo? What about a stock NA PCV fitted on a 7MGTE? Would that work? Can the oil be filtered out? Does a catch can on a sealed system actually remove any of the oil?
What about stuffing some kitchen roll in the stock hoses? :) It's what Brenda would do!
Just a few points that might be of interest. This is only my own opinion and observation so please feel free to contradict me. Sorry that it's a bit long.
The PCV system is a good thing. Apart from blow-by gases, the movement of the pistons and crank creates negative and positive pressure that needs to be relieved.
There seem to be 2 main schools of thought regarding whether a vacuum source aids crankcase ventilation. Additionally there is the argument of whether to use a catch-can or not.
First of all what is a catch can? Basically it is a container into which the PCV gases are fed. The walls of the container need to be kept as cool as possible so that the oil vapour will condense and be taken out of suspension so mounting in cool airflow is a good idea.
Should I vent to atmosphere or follow the stock PCV routing and vent back into the intake? If you vent to atmosphere then the use of a catch can is optional. If you follow the stock system and want to remove the oil from your intake then a catch-can is obligatory.
Points about venting to atmosphere, either with or without a catch-can: It is not very environmentally friendly, although no liquid oil ever seems to come out of mine, oil vapour and other noxious gases are escaping. It can occasionally give an oily whiff when you stop after driving. It does not use a vacuum source to pull the vapours from the crankcase and relies on the crankcase pressure to push/pull the vapours as required. In theory it is better to have the vacuum than not to aid ring sealing.
Points about the stock system and a catch-can: This solution is an improvement on how Toyota designed the PCV system. However, the system is there to help reduce emissions, not to improve performance, so that does not mean that it is the best solution. One point to note is that under boost conditions some boost is lost back into the accordion hose though the PCV link at the throttle body (TB). This boost in theory passes over the valve covers to create a crankcase vacuum. Whether this works in practice I do not know.
Which is the best solution? To keep your conscience clear you should improve the stock system by adding a catch-can. You should also buy a Smart car and recycle your household waste, rainwater, etc.
If you think that the Supra is probably not the most emissions friendly car on the road, but certainly not the worst, then you will vent to atmosphere. The catch-can may ease your conscience but in real terms the noxious gases are still going to escape. Your inlet will definitely not have any PCV oil or gases in it to clog things up or cause detonation. You will save some more boost. This was my final solution.
Further to Lofty's excellent comments, almost every engine has some form of crankcase breather system, which usually vents back into the inlet somewhere, to recycle the blowby gases and help the motor not pressurise itself. (pistons moving up and down obviously create pressure below as well as above, it's a big pump)
Yes, there is an argument to say that the oil in the gas will help to lubricate the bores etc, but in fact the oil just gets burnt, creating carbon build up. It's an emmisions thing, and in fact has pretty much been proven to do more harm than good to an engine. (ever taken your plugs out to find them pretty coked up? mainly oil does this, as most modern fuels burn pretty cleanly)
I've bodged a catch-can setup on mine, initially as a diagnostic aid (If you get a *lot* of oil coming out that pipe, your rings are screwed!) but in fact the motor runs far more consistent. It vents to atmosphere, and yes you do get a smell of hot oil sometimes, especially after a blast.
The best compromise would be a catch can vented to atmosphere, so it would remove the oil vapor before venting.
Also on a side note, venting to atmosphere has the advantage that you are minimising air leaks on the inlet side. As the PVC is in effect a direct pipe from the engine, *any* air leaks anywhere on the engine will result in a lean mixture, crap idling etc. -- eg if your dipstick is a loose fit, or the big rubber crankcase breather pipe (from the crankcase to the front right of the head) is perished/leaking...
Every bike i have ever owned (bar the max) has had crankcase gases vented to atmosphere, either due to original design, or due to mods..
Edit: I went and read the supraforums thread.. hmm. ok, as for vacuum aiding the breathing process, not true. in fact, the crankcases typically are pressurised slightly in pulses with each piston movement, but actually reducing pressure could potentially lower compression (sucking gases past the rings).
As for sealing rings, nope. If the rings aren't sealing, then they are dying/bores are shot.. if you need oil to seal them, then its rebuild time.
lower ring on a piston -- 'oil scraper' -- is designed to remove oil before it gets into the combustion chamber.. why would you want to add oil to the process again?
"PCV" is nothing more than a crankcase breathing system, whatever Toyota/supra nuts/guy in the pub says... (Of course this is my opinion, so feel free to shoot me down .. :) )
(sorry for the long post!)
As for sealing rings, nope. If the rings aren't sealing, then they are dying/bores are shot.. if you need oil to seal them, then its rebuild time.
lower ring on a piston -- 'oil scraper' -- is designed to remove oil before it gets into the combustion chamber.. why would you want to add oil to the process again?
"PCV" is nothing more than a crankcase breathing system, whatever Toyota/supra nuts/guy in the pub says... (Of course this is my opinion, so feel free to shoot me down .. :) )
(sorry for the long post!)
You know, this occured to me.
If you've got a sodding great piston creating pressure in the combustion chamber and you add to that, a vacuum on the other side, then surely the result can't be that you'll "seal the rings". Surely the vacuum will encourage the pressure from the chamber to leak past the rings? After all they do call them "blow-by gases".
I didn't want to say anything 'cos I thought I'd missed something and I was being stupid! :) Come to think of it I propbably am missing soemthing and am stupid! :cheeky:
Thanks to both of you for your incites. I now have a plan.
Jaz Can (with the dinky little baby K&N filter :gay: ) mounted in the cool airflow somewhere with SVH back to a NA PCV pipe. With the throttle body and the accordion hose inlets sealed off.
Now, where can I buy a Jaz Can?
as for vacuum aiding the breathing process, not true. in fact, the crankcases typically are pressurised slightly in pulses with each piston movement, but actually reducing pressure could potentially lower compression (sucking gases past the rings).
I can appreciate how a vacuum in the crankcase could help the rings to seal better in the same way that modern plastic plumbing fittings work, and if there were only 1 piston in a non-vacuum environment I could see that it's movement would cause air to be pumped in and out of the crankcase. But there are 6 pistons and whilst some are pushing air, some are pulling air and I would be willing to bet that for the most part they will cancel each other out leaving a reletively small pressure difference. After all older vehicles from single cylinders to V16s used to use vent to atmosphere systems using relatively small diameter pipes. I'm sticking with my vent to atmosphere until someone can show me proof that vacuum is best.
Good luck with your PCV project, Ian. Bailey Motorsport do a nice polished aluminium 20mm plug for the accordion hose that only needs a small bit of modification (with a hacksaw) if you need one. Part of a plumbing fitting from B&Q provided the other plug for the TB.
nigel w
08-07-04, 05:52 PM
Edit: .....the crankcases typically are pressurised slightly in pulses with each piston movement.....
Hence the name PCV (POSITIVE Crankcase Ventilation)
I agree with Bryank on this one.
I can't see any other reason why you would want to vent the muck from the crankcase into the intake other than to stop it going into the atmosphere as anything other than carbon dioxide or water.
...And as for the vacuum assistance of the PCV theres just no point....the pressure in the case is most likely regulated by the oil filler cap (so don't buy the cheap TRD replicas off ebay!) to ensure that too much pressure can't build and blow oil out of your rocker cover gaskets :) . Plus, the flow into the intake is probably 'metered' by the thingamyjig inside the top of each rocker cover and the diameter of the holes out of the rocker covers.
Search for Crankcase Ventilation on google, it comes up with loads of hits
eg: www.teglerizer.com/triumphstuff/emissions/
torque of the devil
08-07-04, 06:32 PM
lofty, your dead funny. can't beleive you know all that stuff. do you talk to your friends and family about such topics in similar, great detail?
damo_mk3
08-07-04, 11:35 PM
now i've been thinking about fitting a catch can for a bit now and will do in time but
do u think the lenght of the pipe to from the can will have a impact on how the car runs?? i would think so as its more space to suck/vacum thruogh
damo
lofty, your dead funny. can't beleive you know all that stuff. do you talk to your friends and family about such topics in similar, great detail?
He's cool isn't he? :) I love him. :) My Soop would be a pile of doodoo without Lofty! :crybaby:
now i've been thinking about fitting a catch can for a bit now and will do in time but
do u think the lenght of the pipe to from the can will have a impact on how the car runs?? i would think so as its more space to suck/vacum thruogh
damo
Pesonally, can't see it'll make any difference at all. After all, we're venting to atmosphere now and the pipe has a decent diameter.
lofty, your dead funny. can't beleive you know all that stuff. do you talk to your friends and family about such topics in similar, great detail?
I'm certainly no expert. I've been interested in cars and engines for a long time. I try to research the theory behind something and make a judgement whether it be cars, DIY or whatever. I enjoy discussing Supra stuff but I also don't like to bore people so I try and keep it within the community.
do u think the lenght of the pipe to from the can will have a impact on how the car runs?? i would think so as its more space to suck/vacum thruogh
I would imagine that the length of the pipe would have a bearing on the movement of the gases (think of trying to suck water through both a long and a short hose - more effort is required for the long hose) but I wouldn't think that it would make a difference in practice.
He's cool isn't he? :) I love him. :) My Soop would be a pile of doodoo without Lofty! :crybaby:
You are too kind Ian. Thanks.
Wise words there mate!
Lofty is cool! He's a bu**er when he's piss*d tho! :yes:
nigel w
12-07-04, 08:41 AM
...most likely regulated by the oil filler cap....
Nah...had a look this weekend...ignor me! :)
vBulletin® v3.8.7, Copyright ©2000-2012, vBulletin Solutions, Inc.