Trackday Oil Starvation

[MikeE]

I booked onto the Bookatrack day at Goodwood next Monday and was wondering what the situation was ref. above on a Oct 2000 SuperLight 1600. I thought (I must have seen it in the Caterham advert for my car) that I had an anti-cavitation tank. However I went through the original build spec last night and couldn't find anything on there. I also looked under the bonnet and couldn't see anything obvious.

 

How do I know if I have got an anti-cavitation tank fitted?

 

Were/are they standard on this model?

 

If not what other protection does it have to avoid oil starvation (sump baffles?).

 

Is this likely to be a problem at Goodwood (I'm a relative novice and am running standard CR500 road tyres)?

 

thanks for any advice.

 

cheers,

Mike.

[DonkeyDave]

The anticav tank is a big silver turret type canister - looking like the apollo space craft in the left front part of the engine bay, might be just under the nose cone. I thought superlights had them as standard but am not 100% sure. Its connected to the oil filter housing by a sandwich plate.

 

Goodwood is a pretty straight circuit, if you are a relative novice I would have thought you would be ok - if you don't have one - it might be a worthwhile investment if you plan to do more track days.

 

Doesn't really help oil surge but stops the oil foaming too much -

[dino ferrana]

Anti-Cavitation oil tank is not standard superlight spec. It was only standard on SLR's. Having had the R300 spec. it is standard on that now. You can get one fitted afterwards I believe I don't know how difficult it is or the price.

[V7 SLR]

Anti cav tanks were not standard on SLRs or ANY Caterham. They were always an optional extra and don't help in the slightest if you want to combat oil surge. Only a dry sump, or at a pinch an accumulator-type (Accusump is one brand name), can help.

 

Anti cav tanks only de-aerate the oil which is what happens if your oil gets thrashed by your crank during high revving hard cornering. The symptom of this is rattley cam followers. The symptom of oil surge is a grenaded engine.

 

There's nothing standard about CR500s as a tyre. Whilst they're not the last word in race-traction they are pretty sticky and have been developed for the Caterham. They will probably generate enough cornering force to cause oil surge. In fact I've seen worse tyres cause it.

 

You can limit your potential for exploding-engine-itis by not wringing the last out of your car on corners. If you plan to do a lot of track days then you need to spend a bit of cash on engine protection I'm afraid.

[murph7355]

Be particularly circumspect on long right handers. That's where the K suffers most.

 

Anti-cav doesn't address oil surge per se but it does give you a couple of extra litres capacity and does make sure that what oil there is being picked up isn't full of air. Both good things that lessen the chance of you blowing it up.

 

I've only ever seen one Accusump and I'm pretty sure the engine that had it popped. Not exactly a huge sample size, but if you're going to go to the trouble of getting something like it, get a dry sump and do it properly.

 

I personally wouldn't be inclined to take it on a track without an Apollo tank. It's too easy to say you'll take it easy, then forget all about it when you start enjoying youself and finding a rythmn.

[Allen Payne]

I thought the problem was on long left hand corners?

 

Or is it just the the oil pressure gauge is more visable on left handers?

 

 

[murph7355]

I only ever notice it on right handers. A roundabout at the bottom of my road being a constant bane.

 

My engine could be in backwards I guess smile.gif

[V7 SLR]

Anti cav tank doesn't address oil surge at all. Despite the extra overall capacity, this "extra" oil is held outside of the engine sump, so if your oil pick-up comes clear of the oil then you get no pressure regardless of whether there's loads of oil held elsewhere.

 

Funny comment about the Accusump. I think I know whose engine popped that you refer to and can report that he believes that dry sumping is the only proper solution... and can add that another "development engine installation" in another car on tour last year lost an oil pipe and the pressure from the installed Accusump ensured that I, who was following, will never rust. smile.gif

[murph7355]

He's on the list for info on the Pace system anyway smile.gif Wanted to avoid conclusively rubbishing the Accusump route without confirmed details/suspicions. But I think it's safe to say they can be avoided in preference to a DS.

 

I still think the Apollo is a good idea. As PC noted on another thread, the race cars used to use them to good effect. I even know of a few racers who removed their original Caterham dry sumps and used these instead.

 

That said, mine will be coming off when the Pace dry sump is finally fitted to the car (I have a buyer for it already).

[jonhill]

Anti-cav tanks do help keep the pressure up during oil surge conditions.

 

Technically you still get surge, i.e. the pick up is sucking air not oil, but instead of instantly getting no oil supply to the bearings, you still get some, albeit at a reduced pressure/flow. This is because the apollo tank still has oil in it, and it still being pressurised by the air that is pumped into it faster than it can escape out of the vent at the top.

 

On my previous car I used to see the oil pressure gauge dip on the track. Once I fitted the apollo tank this was very much reduced. You can argue all you like about whether or not they should make a difference, the bottom line is that imperially the evidence shows they do.

 

Anti-cav tanks were std on later SLRs.

 

Jon

[V7 SLR]

I even know of a few racers who removed their original Caterham dry sumps and used these instead.

 

Could this be for another reason though? I heard that the reliability of the belt-driven Caterham dry sump was questionable on some racers running at consistently high revs. Perhaps, faced with that as a problem, the Apollo was the only alternative?

 

This is because the apollo tank still has oil in it, and it still being pressurised by the air that is pumped into it faster than it can escape out of the vent at the top.

 

But the standard Rover pressure pump can't provide any air pressure... can it? I understood it to have NO scavenge ability. Are you saying that this is not true then?

 

There has to be another explanation. I wonder if there is a "weight" of oil that the Apollo provides. This weight is obviously not enough for the oil pressure to remain as it is, but might be enough to show a small reading on the gauge.

 

I have to say I remain sceptical about an anti-cav tank providing pressure in oil surge conditions. If it does, I don't believe it's anything other than a weight of oil showing pressure which could possibly be proved by the following:

 

1. If you mount the tank higher (I know there's no room) would this effect be greater?

 

2. If you continue to circle until the tank was empty (assuming the pick up never finds any oil) will this effect reduce as the oil level in the Apollo drops?

 

Obviously point 2 is a baaaad experiment as it means you will eventually run out of oil.

 

If the standard Rover pressure pump does indeed create pressure even when the pick up is high & dry, wouldn't it be a simple thing to reengineer it slightly to scavenge more effectively? I don't know much about pump technology.

 

Where's PC or Oily when you need them?

[V7 SLR]

Oh, and personally I believe an Accusump could be the answer if people could set them up right. Maybe they need to be bigger, but I believe the principle is sound.

 

Or, perhaps a combination of an Apollo and an Accusump? Still cheaper than a dry sump system. Provides both de-aeration and pressure-loss prevention/protection. An awful lot of oil required at oil change though...

[murph7355]

Bigger Accusump? It was enormous enough as it was IIRC. Think of all that weight. And then you slap in an Apollo as well. Easier to go dry sump surely, and perhaps with a reduced oil capacity the saving over time wouldn't be that great. And it'd be less Heath Robinson.

 

No doubt the racers changed because of belt failures or some other issue (the ability of the original dry sump is a matter of record I think). But the point is that if the racers entrusted their engines to the Apollo, then the merit of it as a means of saving your engine on track is proven. Albeit for 20 laps and frequent rebuilds maybe. And therefore for your occasional track dayer it has to be a viable, and more importantly cheap, option.

 

Surely with an additional 50% added to the oil capacity with an Apollo it would be hard to go in long enough circles to completely drain it of oil? Wouldn't the sump fill up and therefore cover the pickup pipe once more and therefore the bad effect of surge is no longer happening as the pipe's covered again?

 

Maybe that's why they help.

 

PS Allen - maybe it is left handers and I was entering the right hander backwards! Stranger things have happened teeth.gif

[jonhill]

Regarding the ability of the Rover pump to pump air, I have to say I honestly don't know for sure. I'm hypothesising, and it seems reasonable to me that a pump will suck whatever it's input pipe is immersed in. In this case air, which has to go somewhere, which means into the apollo tank. I'm prepared to stand corrected, but there is something going on, and this is my best guess. Also, as has been mentioned, what oil flow you do get should be nicely free from any air which will help pressure.

 

Weight of oil? Hmmm, seems unlikely to me given that at least 2 bar is usually required to push the oil into the oil ways. Also the top of the apollo is no higher than the top of the engine, so how far would the oil get anyway?. It's higher than the pressure gauge though...

 

Whatever, there is a beneficial effect, especially under marginal surge conditions, which are likely to be less severe on a lower power, lower revving cars, which *generally* tend to generate less g-force. I fully agree that an SLR should have a DS, and it seems so do Caterham, as they now fit the R400 with one as std.

 

To answer the question about cost of the anti-cav, mine was about £200, and was fitted in an evening. Not too difficult, though it's tricky to tighten the pipes on the sandwich plate once it is on the filter housing. They are attached off the car, but mine leaked and needed further tightening once the system had been run up to temperature.

 

Jon

[Rob Walker]

Jon stand corrected the Rover oil pump cannot pump air it relies on the oil being non compressable in order that it can create pressure by forcing a higher volume of oil through the engines oil ways, this restriction causes the pressure. Pure Air would not be moved through the pump at all.

[jonhill]

OK Rob, thanks for the clarification. A few thoughts on this I have:

 

1) Surely the pump must be able to suck air into it, even if it can't pump it out of the other side. If this wasn't the case, once the input pipe to the pump was uncovered and then emptied, the pump wouldn't be able to re fill it when the pickup is resubmerged.

 

2) I understand that the oil pressure comes from resistance to flow, but I don't see how this prevents the pump from moving air. What is it about air, as opposed to oil, that stops the pump from moving it? Why isn't there high flow of air because there's little pressure? Maybe the seals in the pump rely on the viscosity of the oil?

 

I'm not doubting you, if you say you know for sure, just trying to understand what's going on here.

 

Jon

[Peter Carmichael]

Rob, you are not right. The Rover pump pumps air just fine. The air gets transported from the low pressure side to the high pressure side and heh presto, it may compress a bit, but some volume still crosses the pump and some volume gets pushed through the oilways.

 

Somewhere in the archives you will find my description which deals with the balance between the incompressible and compressible fluids.

 

The net effect is a reduction in pressure. What happens next depends on whether you have an Apollo tank or not. If not, the air gets happily pumped through to your big ends forcibly ejecting the oil film and resulting in bad sh1t. If you have an Apollo tank, the air pressure is enough to keep some oil moving rhrough the galleries - the air gets separated out in the Apollo tank and the oil in the tank makes up the reduced flow into the engine galleries. This oil supply situation has been shown to be quite adequate for keeping modestly tuned engines lubricated. While it is at it, the extra oil coming into circulation helps re-immerse the pickup at the earliest opportunity.

 

Rob, your mistake (and it is a mistake) is to think that the pump creates pressure. It doesn't, it just transports volume.

[groutledge]

I've used 4 pint accusumps before as has two of my friends as I think they're fine. Just put about 17psi in to make sure there's plenty of pressure. Also the manual ones have a faster flow rate (bigger valve). I used to have the tap poking into the cockpit so I could open it from inside.

 

They will deal with corners like Gerrards at mallory and i would expect they would do the job for you.

The trick is to give it about 3000rpm to build up the oil pressure, shut the tap ( hence the manual tap ). and then fill up to the normal full mark.

 

At least that was the trick with Xflows. They will also pre-lube the engine before start up.

 

Not as good as a dry sump but a lot less agg to change the oil.

 

Graham

[Julian Thompson]

V7 SLR is slightly wrong about the anti-cav tank:

 

Anti-Cav tank WAS standard on SLR from 2001 onwards. I know because I had to negotiate to get the price of it knocked off when I specced my dry sump!!

 

(I know it's not much of an issue but there you go!)

[Peter Carmichael]

I have strong opinions that Accusumps are *a bad thing*.

 

Scenario A: "You drive along and cast occasional glances at your worry gauges. Every now and then with your wet sump, under brakign and right hand turns the oil pressure needle wavers. Oh no! Surge! Better fix it with an Accusump. There we go. Drive along, brake and turn right, oil pressure stays good just like a dry sump. Problem solved thumbsup.gif"

 

No. Wrong. The conclusion is based on the wrong assumptions. thumbsdown.gif

 

You don't actually need good oil pressure. Oil pressure is a symptom of an oil system running into problems. What you need is just enough oil flow to keep up with the bearings appetite for oil. What you really don't need is a blast of air at high pressure flushing the oil film out of your bearings.

 

Accusumps treat the symptoms, but do not stop air getting to your bearings. I don't like them.

[V7 SLR]

The accusump is filled with oil (I'm guessing you knew that), so doesn't it depend where you plumb it in which determines whether you push air through the system or oil? I know what you meant though... if there's air between the accusump and the bearings, then regardless of whether the accusump is filled with oil or not, the result would be a period of air flushing the bearing. But surely the only place air can be introduced is at the oil pickup, and once that happens you get immediate pressure drop and the accusump, which is between the oil pickup and bearings, jumps into action.

 

Now, if the accusump had been pressurised with froth over the last few cycles, then you surely would be sending that through the bearings. Couldn't an apollo AND accusump be pressed into service to combat this (this is a theoretical arguement, as no-one could afford to change the oil at "God-knows" how many litres at a time)?

[Peter Carmichael]

Nig,

 

It is much simpler than you are trying to make it. The oil system is sealed apart from the pickup and the bearings. If air gets in at the pickup it comes out at the bearings - whether it comes out when the accusump is operating or not is entirely irrelevant. The pump pushes more oil volume in behind a slug of air and that pushes the air on through the galleries.

 

Normally the oil system is full of incompressible oil. At 4 bar this has the same volume as at atmospheric pressure. If you put volume in at the pump, that volume has to be equalled by flow out at the bearings. If you pump in a volume of compressible air, the air (at approximately atmospheric pressure in the sump) becomes compressed as the pump chamber opens on the high pressure side. As it compresses, its pressure goes up. Equiibrium is reached where the rising pressure of the air is enough to push the *compressed air's volume of oil* out through the bearings. This approximately happens on the k-series at 2 bar. In other words, the pumped air goes from atmospheric pressure to 2 bar above atmospheric (3 bar absolute) and compresses to a third of its original volume.

 

The fluid flow from the outlet side of the pump has two choices: 1. it can flow to the bearings, 2. it can flow back to the low pressure side of the pump through the pressure relief valve. Under surge conditions, the pressure relief valve closes completely, meaning that all of the one third flow is directed to the bearings.

 

Bearings are funny things. They have tiny clearances. If you just ran a pump and tried to push oil through them, you would get hardly any more flow at 20 bar than you get at 2 bar. This is important. When a bearing is rotating, it acts as a little oil pump in its own right, the circular crank journal runs at an offset position in the bearing shells. Oil is supplied to the large gap left on the one side and is dragged down into the working area of the bearing by the bearing's own rotation, generating upwards of 700 bar of hydraulic pressure. Oil gets sucked in at one side and squirted out on the other. The bearing also has a fixed volume that likes to be full of incompressible fluid, so the oil flow in only needs to match the oil flow out. If The bearing's oil supply needs were not being met, the bearing would be sucking oil rather than being fed it and the oil pressure in the galleries would drop to ZERO. The pressure measured by the pressure gauge would reflect the pressure loss of the oil flow through the galleries and through the filter, so would be above zero, but would be a lot less than 2 bar.

 

Remember pressure is the symptom, not the problem.

 

So anything significantly above ZERO bar pressure is OK as long as it is still oil that is going through to the bearings. You would be amazed at how low a pressure is normal in some race engines.

 

When an Accusump comes into action, it maintains the appearance of healthy oil supply, measured in terms of pressure. Because the pressure is high, the flow rate out of the system remains high, but *MOST OF THE EXTRA FLOW IT PROVIDES EXITS OUT OF THE OIL PRESSURE RELIEF VALVE*. Air remains in the system, albeit compressed to one fifth of its original pumped volume (5 bar absolute). When it arrives at the bearing, the air disrupts the oil film; the air can rush through the small clearances much more quickly than viscous incompressible oil.

 

To my mind, it looks like the Accusump was designed by someone who knew how an oil pressure gauge worked but didn't know how engines work. I think they are right up there with snake oil for unsubstantiated claims. Mostly they are fitted to engines that are running at specs that wouldn't fail *without* an Accusump.

[Peter Carmichael]

Nig,

 

I re-read you posting and can clarify:

 

An Accusump cannot *push the air back out at the pickup*, which seems to be your suggestion, because the pressure drop is only evident after the air emerges on the high pressure side of the pump.

 

Once it is through the pump, it needs to be separated from the oil, otherwise it is going to get to the bearings in due course.

 

[ashaughnessy]

I've just been through a thought process that I won't bore you with (or embarras myself with) but the result was this:

 

Does the effectiveness of the accusump depend on

a) How good the oil pump is at pumping air (i.e. can the pump pass enough air to keep the apparent pressure high until the air reaches the bearings)

b) How long the accusump takes to pass all of its oil (I presume Peter thinks all the accusump charge goes out of the pressure relief valve because of the pressure in the accusump)

c) The length of time the oil pickup is in open air (because of b).

 

Is it the case that different mixes of a, b, and c would mean that sometimes an accusump would work (in some engines, on some corners) and sometimes it wouldn't (in other engines on other corners).

 

If you don't understand why I came up with these things, I'll tell you my thought process but I'd rather not display my ignorance straight away.

 

Also Peter, what do you think about the usefulness of the accusump on engine startup?

 

...but, thinking again, I guess all oil pumps on all engines need to be capable of pumping air reasonably well, otherwise how would it suck the oil up the pick up pipe in cases when the pick up pipe had been exposed to open air (e.g. during an oil change). You wouldn't want the pump to take too long to suck the oil up so it would have to pass quite a lot of air.

Anthony

 

Edited by - ashaughnessy on 2 May 2002 14:47:55

[V7 SLR]

Fabulous..!! I hadn't twigged your last point, that about the pressure drop only manifesting on the non-pickup side of the pump, nor had I considered that air could be introduced BEFORE another dollop of oil, thus creating a "slug".

 

I had thought that as soon as the pickup found nothing but air, it would cease to move any oil at all, therefore "no oil delivered from pump yet engine using oil equals pressure drop allowing accusump to fill the void", so to speak.

 

I had also thought that even if the pump tried to push some air through, owing to the inefficiency of the pressure pump at moving air, the resultant pressure would be significantly lower than that which charged the accusump, so the accusump would release its contents and push the air out from where it entered (the pump). Both are flawed arguements.

 

I have another question, this time regarding the Apollo. As the Apollo requires pressure for it to work it must therefore be sealed, so over time won't it fill up with air as more and more aerated oil passes through it. I realise that it is supposed to vent the air from the top, but how does that work without dropping the internal pressure of the whole oil system?

 

 

I love it when I'm "almost" there. It's so exciting chasing those last few details. smile.gif