Oil catch can

[ross_jsy]

When installing an oil catch can, is it recommended to run a line from the breather to the can, and then vent to atmosphere through a small filter or run a return line off the can back to the inlet, creating positive crank case ventilation?

[steve_k]

On an m20 the line goes from the breather on the can cover to the tank then from the tank to the inlet to make it a closed loop, I can't see why it would be any different on a m5x.

[ross_jsy]

Indeed that is a way of doing it, however a lot of installs I see have a small breather filter in the tank instead of the return line. This would be preferable for me as annoyingly I don't have a provision for another line to go into my inlet (alloy Samco jobbie). But if needs must I'll get another with twin ports.

[jimmyspeed]

its mainly for the fume smell in traffic that they get routed back into the inlet

[ross_jsy]

Awesome, little concern to me so I'll just stick a little filter on

[Mikey_Boy]

Be careful here guys - the whole point of an oil breather system is to ensure the oil falls out of the air (by virtue of the large volume in the catch tank) AND to create a small vacuum to ensure that positive crankcase pressure is avoided and all of the oil seals work better - they need a bit of suck in the crankcase to 'grip'. This is why there is a line back to the inlet. Also, be mindful of whether the oil breather is for naturally aspirated or turbo - completely different systems. Most people get oil breathing WRONG - there is horsepower to be had....

[Theo]

Hi Mike, What's the correct plumbing practice for a turbocharged engine?

[DanThe]

From what ive seen proper ones have a return to the sump for the oil

[steve_k]

From what ive seen proper ones have a return to the sump for the oil

That's what I've done on my m20, tapped a hole near the top of the sump (near the dipstick tube) & ran a return pipe into it, thinking about redoing it with a one way/non return valve in it at the bottom.

[jimmyspeed]

so the inlet on a stock m20 is the vacuum and the cylinder head acts as a catch tank ?

as for a turbo i thought it should join just after the air filter and before the turbo - also how does it it gain you power ?

[Mikey_Boy]

From what ive seen proper ones have a return to the sump for the oil

^^^ this...!

Crank case ventilation and piston ring blow by are managed in part by the oil breather system by maintaining the slight vacuum in the crankcase helping everything to seal effectively. Of course the mechanicals are the major factor here, so if you have a worn engine then oil breathing isn't going to save it...

Keeping a slight vacuum in the block helps keep the FMEP (friction mean effective pressure) of the engine to a minimum. Your rotating mass in the engine likes nothing more than to whisk up the hot oily air and keep it hanging in the crankcase - your crankcase is a closed system so air pressure rises here if there is no where for the whisked air to go - the resistance of this gloopy oil air mix rises non linearly with engine speed (if memory serves its the square of engine speed, but I could be wrong). Keeping that in check is a tough job and where effective oil breathing comes in, using the intake (or a dry sump system) to provide a good outlet and vacuum for all that whisked up oil air mix. Also, oil loves to hang in air that is moving, it won't fall out until the air speed drops significantly or the air is spun so the oil flies out. A good example was at Cosworth, the f1 customer engine of the time (HB variant) was down on power - excessive crank case pressure was identified - mods were made to the block to separate each main bearing and the breather system overhauled - net result was 60 yep, 60 extra horsepower on a base engine making about 540hp. For sure, your humble BMW road engine isn't going to see those kind of gains, but the principles are exactly the same - most road car breathers are massively compromised due to cost restrictions and packaging so a bit of thought will reap rewards. A good oil catch tank and the right plumbing should see at least 5-7 hp but, the reliability gains are where it's at - less blow by, seals that work and less horrid oily mess going into the intake lowering your fuel octane..

[Mikey_Boy]

[quote="jimmyspeed"]so the inlet on a stock m20 is the vacuum and the cylinder head acts as a catch tank ?

Effectively yes, the cylinder head is used as the separator and catch tank (the large vents and drains in the head back to the block) with the vacuum from the intake sucking the 'separated' oil in to be burnt...

[jimmyspeed]

sh!t, you know your stuff !!!

i had read about the divided cranks in race engines , but had no idea it was such an important factor on a run of the mill or fast road build, i even thought the only reason it was in place on a turbo car was because you couldn't re-connect to the inlet manifold

edit - thanks mikey, where you the guy who build 2rally cars the end result a white one?

[Mikey_Boy]

No, not me - I just spent my formative years designing and developing race engines...

But thanks for the kind words!!!

[NoTurbo]

Hi Mike, I am trying to install a catch can on my m42 engine. My plan was to run it off the rocker cover vacuum hose and filter the vapour before the throttle body.

You are mentioning crank case ventilation. Should I be plumbing the can into the bottom end instead?

[MillRat]

So, I am correct in understanding that the correct installation should be something like this;

- cam cover breather to an oil catch can
- The oil catch can at negative pressure (presumably by a vacuum line plumbed into the throttle body, with a filter or something in that line to prevent oil vapour entering the intake).
- The overflow from the oil catch can to the sump. Assuming the system was sealed, this would keep the crack case under vacuum.

Or did I miss interpret the above explanation?

[Neilios]

So, I am correct in understanding that the correct installation should be something like this;

- cam cover breather to an oil catch can
- The oil catch can at negative pressure (presumably by a vacuum line plumbed into the throttle body, with a filter or something in that line to prevent oil vapour entering the intake).
- The overflow from the oil catch can to the sump. Assuming the system was sealed, this would keep the crack case under vacuum.

Or did I miss interpret the above explanation?

Thats how I have read it but it would be nice for some kind soul to do a pictorial to show us laymen.

[NoTurbo]

From what ive seen proper ones have a return to the sump for the oil

^^^ this...!

Crank case ventilation and piston ring blow by are managed in part by the oil breather system by maintaining the slight vacuum in the crankcase helping everything to seal effectively. Of course the mechanicals are the major factor here, so if you have a worn engine then oil breathing isn't going to save it...

Keeping a slight vacuum in the block helps keep the FMEP (friction mean effective pressure) of the engine to a minimum. Your rotating mass in the engine likes nothing more than to whisk up the hot oily air and keep it hanging in the crankcase - your crankcase is a closed system so air pressure rises here if there is no where for the whisked air to go - the resistance of this gloopy oil air mix rises non linearly with engine speed (if memory serves its the square of engine speed, but I could be wrong). Keeping that in check is a tough job and where effective oil breathing comes in, using the intake (or a dry sump system) to provide a good outlet and vacuum for all that whisked up oil air mix. Also, oil loves to hang in air that is moving, it won't fall out until the air speed drops significantly or the air is spun so the oil flies out. A good example was at Cosworth, the f1 customer engine of the time (HB variant) was down on power - excessive crank case pressure was identified - mods were made to the block to separate each main bearing and the breather system overhauled - net result was 60 yep, 60 extra horsepower on a base engine making about 540hp. For sure, your humble BMW road engine isn't going to see those kind of gains, but the principles are exactly the same - most road car breathers are massively compromised due to cost restrictions and packaging so a bit of thought will reap rewards. A good oil catch tank and the right plumbing should see at least 5-7 hp but, the reliability gains are where it's at - less blow by, seals that work and less horrid oily mess going into the intake lowering your fuel octane..

When you say crank case do you mean under the rocker cover or the bottom end of the block?

[swainerjim]

pictures would help alot of people here including myself cheers

[Mikey_Boy]

So, I am correct in understanding that the correct installation should be something like this;

- cam cover breather to an oil catch can
- The oil catch can at negative pressure (presumably by a vacuum line plumbed into the throttle body, with a filter or something in that line to prevent oil vapour entering the intake).
- The overflow from the oil catch can to the sump. Assuming the system was sealed, this would keep the crack case under vacuum.

Or did I miss interpret the above explanation?

^^^ yes, you are correct in stating this - you can delete the drain back to the sump if you like (if the separator in the catch can isn't great then some nasties can end up back in the sump, the only problem with not having a drain is you need to regularly empty the catch can).

Let me try and dig out some pictures to show a schematic...

[Mikey_Boy]

@NoTurbo - when we talk about crankcase breathing, generally that means the whole engine system, so the block and the head combined - most road engines link the block and the head somehow so your pick up point is pretty irrelevant - most BMW engines have had a fair crack at it and any improvements will always help - others (e.g. ford pinto, Austin a series) are utter rubbish - both are seriously compromised!!

[Mikey_Boy]

And in the ideal world, you would have a pick up from both, the block and the cam cover. Positioning is key though, otherwise you just end up whisking and force feeding oil from the bottom end through the breather - not ideal!!

[NoTurbo]

And in the ideal world, you would have a pick up from both,

Thanks for the feedback Mikey_Boy Currently on my car,the top end breather pipe from the rover cover is connected to the catch can and I vent back via the TB boot. Where would I take the bottom end feed from?

Excuse the question, but its not really obvious where I would take the breather feed from..

[Mikey_Boy]

No worries - let's see if we can make things a bit better!! Which engine are you running??

[NoTurbo]

M42 318is.

I need all the horses I can get ! Haha

but, in all seriousness my car gets pushed quite hard in Autosolo, sprints and track days so I am looking for a solid solution.

[Mikey_Boy]

Not an engine I know a lot about if I am honest. However, I would suggest improving the current set up by incorporating a catch can into the cam cover breather hose as a start. I would go for the largest volume can you fit in to the engine bay (ideally 2 litres or more) and plumb it effectively(a few sharp turns in hoses as possible). The catch can needs to be part of the closed circuit as I outlined above - the return from the can needs to go back to the intake system as defined by BMW. At first I would NOT put a drain back to the sump, instead I would suggest monitoring just how much gunk and oil gets collected in the catch can. It's also worthwhile to monitor your overall oil level after fitting a catch can to see if any oil consumption issues improve or get worse.

Good luck and post some pictures if you do decide to go down this route...

[NoTurbo]

Thanks for the help. This is the route I was thinking too. Pics to follow soon

[MillRat]

Thanks for the help. This is the route I was thinking too. Pics to follow soon

Any luck with those pictures?

[NoTurbo]

Not had time to fit it yet. I have been busy with other parts of the engine. Fitted itb's cop and new disks pads etc.

I need to make a bracket for the catch can which is holding me up.