silent running

As the title says...

With a VTA breather system, I just cannot see how it can possibly work as well as the standard system which uses vacuum to draw on the crankcase all the time, replacing this with fresh, metered air from the inlet pipe. Putting the question of whether it is right or wrong to let the engine burn this all off to one side for the moment; someone please explain clearly how a vented system can even get close in efficiency to a sealed system which uses engine vacuum to scavenge out the vapours? And if scavenging becomes less efficient, what is the upshot of this? More contaminated vapours sitting around? Harder work for the pistons having to push out all that stagnant air without any help from intake vacuum? That's a hell of a lot of air to be shifting around in each cylinder. The other thing that strikes me is that as designed, the breather system is more a throughflow system than simple outflow. With an open breather system, I can't see what 'breathing' is actually going on as it can't replicate the in-one-end-and-out-the-other of the OE recirculating system. It's just blowing out a little when on boost, surely? The rest of the time you've got two or three pipes open to the elements going straight into your engine.

I know a lot of people vent out their breathers to atmosphere either straight out, or via a catchtank. I had a recirculating system going through a catch tank which worked fine, and I now have a VTA system which seems to work but then it's hard to tell. What I do know is now my fuel economy is 10-20% worse (although this could be something else), I've got oil residue all down my exhaust centre pipe and slight mayonnaise inside my oil filler cap, which I have never, ever had before. I run a sports cat, so the 'it's only the same composition as exhaust gases' argument is neither here nor there, for me at least.

So let's hear some opinions that can convince me I'm doing the right thing sticking with open breathers, before I go and spend £200 on a Samco inlet hose so I can plumb everything back to how it was before.

silent running

bttt

ZEN Performance

When does the engine breath the most? When it's on boost.

A little? No, a lot.

jd5217

Paul Daniels???

silent running

But is it better to let the engine push the crankcase vapours out, or to have them drawn out by a vacuum?

jasonius

iTrader: (1)

Can't say either way, but I had the same thoughts when I first did mine, +2yr ago..!

I the end I just stuck with it and everything seems fine 28k on. Don't get any drips/mayo nor did I notice a change in mpg. Certainly dosen't effect performance.. No longer get loads of oil residue gungeing (sp?) up inlet/IC either..

I would be interested to know more though, Paul, care to elaborate- if you have a spare few mins that is..

Northern Nick

iTrader: (1)

I have a total VTA, PCV delete breather system on mine, I've never noticed any so called "down sides" to doing this.

Car runs fine, no sludge, no smells, no leaks.

ZEN Performance

Where are you going to get this vacuum on boost?

silent running

Well on boost, surely there will be one hell of a draw/high speed airflow through the inlet pipe, therefore any smaller bore pipe teeing into it, will naturally 'see' a vacuum effect. This is exactly how the original recirculating system works when on boost, does it not? The PCV shuts as you've got boost in the manifold, meaning the only open route for crankcase ventilation is teed right into the inlet pipe, which is drawing vacuum on every open hole that it has along its entire length including of course, the filter on the end of it.

Have I misunderstood something here? Is that not a vacuum drawing out crankcase fumes while on boost?

I'm just interested in this kind of stuff, that's all. It seems to me that by opening up all the breathers, you're making more work for the engine - pumping losses IIRC? By keeping the vacuum/recirculating system, you're getting half of that work done for free. I'm not debating whether it's a good idea to have oily vapours blowing through your intake - that's a no brainer. But what I am curious about is the effect that it has on engine efficiency by making each piston move half a litre of air out of the way every time it descends. I'm not saying that with the recirculating system connected up you've got a hard vacuum in there, of course not...but it must make the work of the engine a lot easier.

In fact, don't some race engines use dedicated vacuum pumps to run the crankcase pressure right down without the disadvantage of having to burn the gases off?

saiklon

I VTAd my breathers 3 months ago and the car immediately - like within one hour - started leaking oil. I suspect my oil seals might have been on their last legs and the VTA breathers probably caused more pressure in the crankcase

I also did not notice any improvement in performance with the breathers VTAd. I therefore had the oil seals replaced and put the breathers back into the intake.

I'll just invest some time every few months to clean out the IC of the oily residue it gets.

silent running

Well I think all I need is a better designed catch tank that will actually do more to condense the oil vapours. But I must say the whole time I had my recirculating system plumbed in, interecepted by a catch tank, I had virtually no problems with oil in the inlet side.

Adam K

I had, for a while, a VTA via catchtank, and on rocker cover breather side, a filter, which happened to have a tray below it. I didn't notice any performance difference, but the tray got filled up with oily residues quickly.
When I fitted a return to inlet hose from the catchank that tray stayed dry (except in winter when sometime the hose to the catchtank froze, and on tracks with a lot of high boost driving).
In abt 2 years the catchtank filled up with a mustardy cream (yes I emptied it until it stopped flowing/dripping now and then).
I don't know what whatever does for performance or engine life, but there is a noticable difference.

Peanuts

iTrader: (15)

I used to run VTA breather mod, stops the oily crappy air being drawn back in, there is a huge thread over on 22b about it, I think its called "PCV delete".
Now I spend more and more time on track I had to install a catch device to prevent it pouring out onto the black stuff.
so I used an oasis bottle, 79p later and its all groovy.
5m or so of 1/2" B&Q domestic hose chopped off the end of a neighbours reel when he wasnt looking
its all good baby

Welloilbeefhooked

iTrader: (3)

When its on boost air is being drawn out of the rocker vents and the crankcase vent into the inlet pipe as the PCV is shut. Therefore there is NO air being drawn into the breathers at all.

Does this help?

Wayne.

silent running

I think we both agree on that anyway? The vacuum of the inlet pipe is drawing crankcase gases out while on boost, and the rest of the time the vacuum of the manifold is doing the same job, via the PCV valve. These effects are both lost when you open the breathers up to atmosphere.

Torben

You can also run a closed system if you are running high boost and trackdays, so the oil just is running back from a tank into the engine. Like this Crawford Performance

silent running

Now that's a nice idea. No mess, no waste, no burning off precious oil (Silkolene Pro S doesn't come cheap!)

silent running

Well I've done a bit of disassembly today and the results are; my twin breather vent pipes coming from the catch tank down to the gearbox area were full of oil/water residue, rather more like liquid batter mix than mayonnaise! The catch tank was virtually full of the same foul mixture and even the breather pipes into the catch tank from crankcase and rockers were wet with this stuff. Nice. No wonder I was seeing mayonnaise at the oil filler cap which I'd never had before. I dread to see what my oil will look like when I drain it.

Well at least that's decided one thing for me - opening my breathers up to atmosphere is a big no-no from now on - I'll go back to standard with my catchtank intercepting the return lines into the PCV and inlet pipe. Maybe it's just my engine has a lot of blow-by, maybe it's the cold weather, maybe it's the kind of driving I do, maybe it's down to lack of vacuum, maybe it's because with an open system you never have any actual fresh clean air circulating through...but whatever the reason, I think my doubts were justified.