Dry sump

[John Howe]

Whilst I wait, with fingers crossed, for Pace's dry sump kit to become a reality... does any one have any views on an alternative to Caterhams dry sump kit

 

 

[Rob Walker]

I think you are in for a bit of a wait and hope you are ready for some serious spannering. From my chat with Pace at the Autosport show the system is still in a developement stage and will require quite a lot of work to install the system.

 

One of the biggest jobs being removal of the engines oil pump internals " the Anulus and rotor" this will necessitate the removal of the Timing belt cover,crank pulley, timing belt, oil pump and blanking off of the existing oil feed gallery from the oil pump.

 

Patience.

[garyedwardc]

I don't see why everyone is lusting after the proposed Pace system. I see the main drawback of Caterham's version as the bellhousing tank. Put a proper crossflow type tank in and most of the problems go away. Suddenly you can have as much oil capacity as you want and the oil is de-aerated in just the same way as with an apollo tank so you dont have to add one of those. The oil tank doesn't fry your clutch which only leaves the question of whether the in-engine pressure pump is up to the job and whether Pace can design a better dry sump pan than Caterham. Thankfully Vx engines don't seem to be such a problem, except for the oil leaks.

[Jason Plato]

I agree that the solution to the caterham setup would be to fit a seperate sump tank as I suggested to Peter Carmichael , this would also mean you wouldnt have to remove the engine to fit a new system .

But there are other comprimises with the caterham set up - height location of scavenge pump , single scavenge .

Although many people are happy with the performance of this system unless you are using stratospheric revs for long periods .

 

dave

[Rob Walker]

I think the pace sump pan is techically a better design than the Caterham pan in that it has two scavenge pickups, however I didn`t like the thought of the external 3 port oil pump being driven by a rather flimsy toothed belt. Loose this belt and your engine is instantly spoilt.

[Peter Carmichael]

I don't like the sudden death belt driven pressure pump on the Pace system. The internal oil pump is up to the job - just about. It can be an idea to replace the rotor with a QED spark eroded one at stratospheric revs.

 

The Caterham pump location and single pickup arrangement are compromised. The tank isn't that bad, although extra tank capacity can mask a lot of other evils.

 

Running sealed is a silly idea and I don't do this any more. I have a filtered breather on the cam cover and this helps drainage from the head. - I have been able to measure this effect in the data logs, so it really is happening, but my engine has more problems than most. Scavenging directly from the head would be the ideal solution.

 

The packaging of the dry sump bellhousing tank is a strong point for me. I can keep the long passenger footwell and I can remove the engine without draining the oil.

 

A Pace system for half the price of the Caterham system will find a market, but for me I would be looking for a better pump and pickup arrangement to complement the bellhousing tank, rather than the other way round.

[Rob Walker]

Peter,

 

Running the system sealed is a bad idea, I don`t do this any more. Would you like to elaborate Peter. I have been plagued by a small oil leak from the area at the rear of the engine and suspect the crankshaft rear oil seal is been distorted by running sealed. This small leak occurs after the car has been stood for a few days and some of the tank oil has drained into the sump. I have resealed the sump pan three times but to no avail and now suspect this seal.

[The Pied Piper]

I run a sealed Pace dry sump system on my XE, in a rally car. The engine stays completely dry, no leaks at all except when I leave it standing between events. The oil from the tank which is higher up than the sump gradually fills the sump and then I get a leak from the rear oil seal. I spoke to Pace at the show and Neil suggested that it is the vacuum remaining in the engine that actually helps to pull the oil through the pump and into the sump. He suggests fitting a release valve to the block to release the vacuum during storage. Other than this the system has been superb over a the last 3 years, only failing when a damaged piston caused pressurisation of the block and blew out the half moon seal at the rear of the inlet cam cover. Also, I have never had any problems with the rubber band!

[oilyhands]

Dare I mention that the Pace system has a target price around 4-500 pounds less than the Caterham system...

 

The dry sump kit on the QED stand for the Elise looked very good.. £1100 buys you a system with a three stage pump which looks powerful enough to give a fair vaccum in the sump, a cunningly designed sump pan with two take-offs and all the necessary oojamaflips to make it all work including a toothed belt pulley, spacer to replace the pump rotor etc.etc.

 

Rob, the rear seal is particularly vulnerable on the K, early ones have a very fat lip (.. pardon?) which is largely unsupported by the outside of the seal. This makes it prone to 'popping' when crankcase pressure is different to atmospheric.

 

Oily

 

Edited by - oilyhands on 17 Jan 2002 14:05:11

[Peter Carmichael]

Here is a posting that I wrote for another forum that describes why sealed systems are a bad idea. I really don't care that much about the oil seals when there are much larger concerns at work:

 

If the R500 engine is sealed, it *always* runs with an internal vacuum. My plugs on the cam cover are not restrained so if this wasn't the case they would pop. I have not yet heard a decent explanation of why a sealed system and a vacuum are advantageous. People (including Pace Products who design dry sump systems) have a very strange idea about the physics of vacuum pumps believing that the pump will always succeed in scavenging oil even when *there is hardly any crankcase pressure pushing the oil into the pump chambers*.

 

Forget about absolute pressure. Look for the pressure gradients in the system. Look for where they are desirable and where they are undesirable.

 

There are two pumps (scavenge and pressure) in the system. The pumps are fixed volume pumps. For one revolution of the crankshaft, a fixed volume is transferred from one side of the pump to the other. However in the pressure pump's case this isn't quite true...

 

The engine's running oil pressure is developed by trying to squeeze a flow of oil through the galleries and into the bearings - the flow is resisted until the pressure builds up to the point where the pressure relief valve opens, bleeding off some volume back to the low pressure side of the pump. In this way, the flow of oil into the engine is regulated to meet the demands of the engine. At higher revs, the bearings need more flow of oil (the oil spills out of the side of the bearings quicker), the pump is turning quicker and the pressure relief valve modulates to maintain the 4 bar (or so) that are required.

 

For the scavenge pump there is a subtle twist in its behaviour...

 

There is equilibrium - if this wasn't so, the engine would either fill up or empty of oil. The amount of oil pumped into the engine must, on average, equal the amount pumped out. The scavenge pump pumps oil and fumes and any foaming combination of the two it finds at the pickup. Sometimes the scavenge pump sucks only air and fumes. When the pickup is next immersed in oil it has to *catch up* and pump oil out of the engine at a faster rate than the oil is being pumped in. This process is regulated by making the scavenge pump of a larger fixed volume than the pressure pump (approximately double) and scavenging until the sump is dry.

 

What this means is that the *volume* exiting the engine is larger than the *volume* coming into the engine. We know from the principle of equilibrium that the *mass of oil* exiting the engine is the same as the *mass of oil* entering the engine. The scavenge pump is of fixed larger volume, but the fluid it is pumping is variously made up of oil and fumes, the proportions of which balance out until equilibrium is achieved.

 

There is another flow of matter into the sealed spaces of the engine - blowby of combustion gasses past the piston rings. Let us first imagine that this blowby did not exist:

 

The scavenge pump evacuates, on average, the volume of oil as pumped into the engine and additionally some fumes/air. If the blowby gasses did not exist, the accumulated evacuation of fumes would eventually lead to an almost complete vacuum. At this point we have to look at how the oil gets from the pickup to the pump chambers which are mounted half way up the block. The scavenge pump chambers open on the pickup side essentially with a complete vacuum. If the sump itself has been evacuated to the point of a complete vacuum, there is no pressure gradient up into the pump - there is no push of air pressure forcing the oil up the pipe and into the pump. Without blowby, the engine will scavenge itself to complete vacuum and then the scavenging will stop. BANG!

 

But we do have blowby, so the scavenging doesn't stop. What we must be wary of is people telling us that deep vacuums in the crankcase are a good thing. With the pump mounted high up on the side of the block they are very dangerous indeed.

 

These same people happily tell us that the vacuum also helps the head to drain down to the crankcase - "there is no air in the way". WRONG!

 

Let's picture our perfect equilibrium. Oil in equals oil out. This is as true of the head as it is of the sealed engine as a whole. Oil is getting pumped into the head and is draining out at an equal rate.

 

You then go around a corner and the oil drainage halts for a while with all the oil trapped in the side of the head - all the while oil is still being pumped into the head. After the corner, the oil drainage now needs to catch up with the extra retained oil in the head. The oil sloshes back to cover all the drain holes and the head is effectively sealed off from the crankcase, but having just been open to the crankcase, both head and crankcase have the same equilibrium pressure. Oil coming into the head pushes oil down the drains. If the oil drained any quicker, it would cause a pressure drop in the head and there would then be a pressure gradient holding the oil in the head, matching the depth of oil (say 1 inch of oil = 0.75 inches of water = 0.002 bar). 0.002 bar is not a lot of pressure and it is all that it takes to hold the oil in the head.

 

If the drains are appropriately large, this won't be a problem. In the K-series I think there is reasonable evidence that the drains are too small and there are problems with oil retention in the head at high rpm.

 

So how do you prevent this? Simple really. Fit a filtered breather to the cam cover. In any circumstance where *all the head drains* are immersed with oil, you will get accelerated drainage of the head. Its by no means perfect but it may help in critical conditions.

 

In truth, all you need to do is guarantee that some extra volume of air gets into the cam cover. If you know what the normal, sealed equilibrium vacuum is, you can arrange a spring loaded valve with a pressure drop that will open just above the equilibrium pressure. You know the flow is always going to be into the engine, so this can be a common one way valve with a rated pressure drop.

 

 

[Peter Carmichael]

At my first track event with the new engine I ran sealed, with fixed (low) rev limits and gradually upped the revs with close monitoring of the logs looking for the Apollo tank coming into play. The Apollo was coming into play at the end of long straightswhen using above 7900 rpm.

 

I fitted a filtered breather and the oil pressure drop characteristic disappeared

[oilyhands]

One advantage of running a partial vaccum in the sump is in the reduction of windage, at very high RPM this can be a power sapper, whether it costs you more in parasitic losses to maintain the PV than you gain from reduced windage is hard to say.

 

Some motorcycles employ a device attached to the exhaust to help evacuate the crankcase.

 

Oily

[murph7355]

I thought I'd posted this before but must have dreamt it (oh no!).

 

Anyway. I'm sure Pace said to me, when I took the car up for measuring as a template, that you wouldn't *have* to remove the internal pump (by "disabling" a stage of the pump?). They were also trying to do it so the engine didn't have to be removed.

 

The pan, as mentioned, has two pickups which I believe is good. And the pump will be better situated (due to the pump design and a modified engine mount), which I also believe is good.

 

You can run them sealed or not, whichever suits.

 

And the original target was for all the bits to come in at around 1100 notes which is 600 less than the Caterham system I believe. Maybe more.

 

As there are going to be loads of options for tanks, I'm sure you could retain the bellhousing tank if it suited and swap the pan/pump? This'd reduce the Pace system in price by a good chunk.

 

They also state that they may be able to do something for head scavenging (extra cost mind).

 

The only problem is that they had some issue with the first castings which has delayed the project. How much delay, I don't know yet.

 

I wonder where the Elise one's pump was mounted and how.

 

My reason for looking at Pace is that I don't want to spunk 1700 notes on something that is known to have flaws that can, theoretically be overcome. Then again, I bought a 7! Pace's operation also seems top notch to my inexperienced eyes, and if people like TWR use them. Well who am I to argue.

 

Still, will see what they come up with and make a call then I guess (which'll give me time to figure just why my engine seems to be drinking a lot of oil at the minute! More expense no doubt).

[oilyhands]

The Elise pump is mounted on the exhaust side down low.. but above the filter housing.

 

Oily

[robmar]

would you have to fit the smaller alternator - like the one on the qed stand at the autosport show to fit the pace system

 

and just out of interest is that the side PACE suggest fitting in a caterham?

 

rob

[Rob Walker]

No Rob the Pace Pump is mounted in virtually the same place as the Caterham . On a modified engine mount off side. Andy, doubt you could use the Caterham bell tank with the Pace sump pan as the Caterham Bell tank is clamped/bolted through the sump pan. It is possible to remove the oil pump internals from the stock K oil pump with the engine in the car. The point is this requires some fairly technical spannering which may be beyond some peoples abilities.

[Rob Walker]

Pied Piper, your posting makes sense and is a possible explaination for my oil leak. I had trouble getting my head round why the seal should be distorted whilst running because the seal will be pressurized by the oil pump to whatever is normal oil pressure. The problem must occur the moment the engine is switch off and oil pressure will imediately decay allowing any remaining vacuum within the engine to pull the seal in or away from the crank surface. Then after a few days as the sump pan fills we have a small oil weep. I shall release my cam cover oil filler cap and allow air into the engine before switching off and see if the problem goes.

[Lawrence_Z]

FWIW

The QED Elise pump is fitted in place of the oil filter housing and therefore requires a remote filter. at extra cost :)

 

The old Lotus twincam had problems with oil retention in the head and they fitted a bypass hose from the head to the sump.

 

Why can't the K have an extra return pipe fitted externally?

 

just my 2p

Lawrence

[oilyhands]

Lawrence,

 

an oil drain could be fitted, but the design of the head and the angle of installation means that oil collects in several discrete places, each would need a drain.

 

On some of the heads I have done I've mad a mod to the drain holes /bolt holes to allow oil to drain more rapidly from the areas where it pools. It's hard to measure its effectiveness though.

 

Oily

[Rob Walker]

Oily,

 

I recently measured all the oil retained within the head after running the car and quickly removing the cam cover. 750 ml of oil was removed using a syringe . This represents about 12% 0f my oil capacity, obviously the retention will be greater when the engine is running and at higher revs.

[Johnty Lyons]

I don't think the spannering will be a problem to anyone on here who is contemplating a pace system most of us and I believe [andy correctr me if wrong]there are a fair few are in the middle of major engine mods anyway, The bit which worries me is location and capacity of the oil tank I would like 5ltrs but am having major problems in finding a suitable location, It mat be possible to slightly shorten the pasenger footwell at the top only where it protrudes around 40mm past the batt tray without actually shortening the foot space [the top bit is unused inside the car]and thus squeeze in a tank behind the headers, the other option that Mick and I discused was a special tank rect at bottom and circ at top betwen the rad and the timimg cover. Any other bright ideas???

[Rob Walker]

Johnty,

 

If you don`t run with a heater or could do without one then mount the tank directly above the gearbox within the transission tunnel sort of halfway through the tray infront of the front bulkhead/scuttle. Alex Wong has this installation. It necessitates cutting a 9" hole in the tray and having a tank mounting plate welding on the tank half way up its height. Very neat when done.

[murph7355]

Whenever anyone has a problem with tank position it's because they want to keep all this nice stuff.

 

I find it easier to only carry short passengers. Also gives me an excuse never to end up as the passenger myself.

 

Next step is to fit a 20 gallon fuel tank where the passenger seat used to be.

[Alex Wong1697456877]

I can e-mail pics to anyone who wants to see the installation. It's done 10 trackdays and 6,000 road miles with this drysump arrangement and has been fine.

 

Alex

[Alex Wong1697456877]

There's always the brise 2 tired tank - search in techtalk.

 

Alex