Dry sump ... moving from a sealed crankcase to vented ...?

[SLR No.77]

I'm planning to swap my sealed dry sump install (Rover K) to vented. I ran my last car vented and I believe it puts less strain on the seals and will stop the "clucking" that exists at tick-over. It should be a straightforward job by teeing off the hose that runs from the tower to the catch tank, and linking it to one of the 2 vents on the cam cover ..... but unfortunately I can't remember which vent is the in and which is the out!

I seem to recall the forward one is the correct one to use but can anyone confirm?

 

Stu.

 

Edited by - sforshaw on 6 Mar 2013 11:32:23

[7 wonders of the world]

Keep it sealed, vented only allows more air to be pumped around the scavenge circuit, meaning more de aeration is required, there will be less of a partial vacuum in the crankcase too which will increase windage.

[SLR No.77]

Why?

 

Stu.

[Englishmaninwales]

Stu

Run it vented.

If TBs, then front vent to catch tank. Rear vent filtered air in. Swirl tower vent to catch tank.

If plenum, front vent to plenum rather than catch tank.

Fix the catch tank low down on chassis and vent under car.

Run these ways for years, no probs

 

Edit to add: vacuum/partial vacuum in crankcase must surely reduce the ability of the scavenge pump to work efficiently. Remember this is a poorly designed DS system, it requires ALL components to be at maximal performance to lessen the risk of oil starvation

 

Edited by - Englishmaninwales on 6 Mar 2013 12:28:15

[SLR No.77]

Quoting Englishmaninwales: 

Remember this is a poorly designed DS system, it requires ALL components to be at maximal performance to lessen the risk of oil starvation

This features strongly as well .... having already lost the engine due to oil starvation anything that will improve scavenging quickly moves to the top of the "must do" list.

It's a VHPD, Caterham "Gold" dry sump system and running roller barrels. Only one vent on the swirl tower, 2 vents on the cam cover and I have one inlet on my catch Mocal tank (second is the vent). The catch tank is below the outlet from the tower but getting it lower than the cam cover may prove difficult due to limited space ... might need to do some head scratching on this one.

Quoting Englishmaninwales: 

If TBs, then front vent to catch tank. Rear vent filtered air in. Swirl tower vent to catch tank.

Why does it need both a filter and a catch tank connection to the cam cover?

 

Stu.

[TomB]

My DS system only has the two breathers on the top of the cam cover, one goes back to the DS tower and the other goes to the catch tank. Cant remember which way round they are, will check later.

[Englishmaninwales]

[pQuote]Why does it need both a filter and a catch tank connection to the cam cover?

 

Stu.

The rear vent is connected to TB airbox and draws filtered air in (or from TB on old supersport plenum) and the front vent blows out, safest place is to the catch tank.

 

Edited by - Englishmaninwales on 6 Mar 2013 13:21:25

[skydragon]

Mine (K-series with TB's and CC dry sump with Pace tower tank) has the rear vent blocked off and the front vent run back to the 2nd connector on the Pace tank. The centre top connector on the Pace tank then feeds into a remote catch tank. An outlet on the catch tank then feeds (via a long pipe fed down underneath car) to open air.

 

Good simple system and has worked perfectly for 2 years and is system used on many other cars.

 

Have a look at this photo here

 

Edited by - skydragon on 6 Mar 2013 13:43:26

[TomGaval]

Here is an old post that discusses the issue and solution that I consulted with on my system. Hope it helps. Tom

 

here

[SLR No.77]

Thanks all

Tom(G), I've read that thread before and it was Peter's comments that convinced me to run vented. I've still struggled to fathom the correct pipework though!

So ....

1. Malcolm, I'm running a large airbox therefore I assume you're suggesting to pipe from the pack of the airbox/backplate to the rear vent on the cam cover to create a filtered air input?

2. The second (forward) cam cover vent should then be piped to a catch tank.

3. The d/s tower should be vented to a catch tank.

4. The catch tank should be vented to atmosphere somewhere below the car.

 

But, for 2 & 3, can these somehow be linked? My catch tank only has 1 in, 1 out.

 

Edited to add ..... my Mocal catch tank actually has 2 inlets although most people use one as the inlet and one as the breather. If I re-piped my setup to use both as inlets, is the "vented cap" good enough to vent the system or do I need to get my drill out? This would solve 2 & 3 above.

 

Stu.

 

Edited by - sforshaw on 6 Mar 2013 17:07:49

[Shaun_E]

Dry sump tower to rear vent and front vent to catch tank is how I ran mine.

[Willie.]

 

 

Edited by - Opposite Lock on 6 Mar 2013 20:19:25

[Willie.]

Hi Stu,

 

For what it's worth, in the original setup of K breathers on standard engines, one goes to the atmospheric side of the butterfly, and the other to the plenum side of the butterfly.

 

In my understanding of it, this means the crankcase always has an atmospheric breather, but it also can see a depression in the plenum (Throttle closed at revs). The depression means the atmospheric breather is a higher pressure, and so it'll circulate clean, filtered, air into the crankcase from atmosphere, and out into the lower pressure of plenum and into combustion process.

 

On some cam covers you'll actually find a tight wire gauze behind the out (Plenum) breather. This is to stop too much oil mist being drawn into the plenum. I once ran a cam cover without the gauze, and very high oil level (So lots of windage & mist). If you were doing high revs then shut the throttle, next time you gave it throttle a Jame's Bond style smoke screen was activated. Plenum was coated with oil inside. I concluded it was being pushed in by atmosphere when plenum in depression (Poor plenum 😬), pooling in the plenum as no real air flow until you opened the throttle when the airflow carried it in.

 

That's just my experience/conclusion on what the breathers are doing. Just might help you understand what's going on a bit better so you can work out how to route your breathers.

 

For example, if you put one to your airbox backplate, and the other ends up atmospheric, you'll be replicating the original system, so what you might assume to be a "filtered clean air into crankcase" is actually the crankcase oily mist out (And into your roller barrels).

 

I could never really understand why you would need the one connected to the plenum in the original setup; but just read that Peter C post and that makes sense. It's been said that K heads tend to be slow at draining oil, and so the plenum breather would be the way of helping this. When you've beeing lacing it at high revs and there's a pile of oil in the head, when you shut the throttle, the depression means it'll get it all back into the sump quicker than it would if purely atmospheric.

 

Hope some of that helps; just in from a wet single speed commute, so in a waffling mood. Sorry.

[david nelson]

I have run mine as per Chris's photos but we both have the pace easy clean tank.

 

David

[SLR No.77]

A bit more research done and also some information from a very interesting article in Racecar Engineering magazine (thanks Sean ) which was written in conjunction with Graham Fuller (Minister Power), added to all the information here and I think I've an idea of what might be ideal ... which as with anything Caterham & K-Series usually results in a compromise! Amazing the difference a day makes in the learning process!

 

I'm assuming a throttle body (non-plenum) install only:

1. Sealed is better to reduce windage and minimise aeration …. but may not be viable when considering the limitations of the scavenge pump!

2. Particularly with a cold engine it's possible that the cam cover output breather tries to blow oil out ..... this can be fed back to the main oil tank (bell-tank) or a catch tank. If running sealed this needs a non-return valve.

3. The oil tank (belltank) is vented to a catch tank.

4. The cam cover inlet breather is either blanked off (sealed) or can be fed with filtered atmospheric air (unsealed).

5. The catch tank is vented under the car.

 

The various suggestions include a combination of most of these, but for a standard Caterham K-Series install using a bell-tank ....there’s not enough inlets/outlets to do everything! Ideally an oil tank is needed that has twin breather inlets (like Chris’s photo) or a catch tank with 2 inlets and a separate breather. My Mocal tank would do this if I accepted the breathing was purely through the cap but that would result in some nasty fumes in the cockpit.

 

So I have an idea ..... there’s a second inlet on the Caterham bell-tank that was used prior to the addition of the tower – I’m going to investigate linking back to this from the cam cover output breather, similar to Chris’s install. The breather on the tower can therefore remain fed to the catch tank with the second catch tank connection working as a breather and fed under the car.

Any oil expelled from the head will return to the bell-tank, and additionally any excess oil in the whole system will be expelled via the tower into the catch tank as per usual.

 

With this plumbing done I have the choice of running sealed or not. Sealed would be achieved by blanking the inlet breather on the cam cover and fitting a non-return valve in the cam cover feed back to the bell-tank. Unsealed would need (as per Malcolm’s suggestion) a small pipe from the airbox to the cam cover inlet. I think even if not sealed the return to the bell-tank should have a non-return valve. So no acid fumes going into the engine and no oil being fed back through the TB's.

 

For now I need to give my head a rest! Thanks all for the suggestions

 

Stu.