Thought I'd write a quick article on how to build a dry-sump system that doesn't cost heaps and is not too hard to make. Too many people either get it wrong or pay way to much for them, and that shouldn't happen.
This is a rough schematic of how most systems look.
You can see that there's a lot of oil lines running around the engine bay (seven) and that opens you up for excess weight in a racing car and also excess complexity and a greater chance of leaks and things going wrong.
Fortunately, there's ways to reduce the number of oil lines and simplify things somewhat.
With a little clever engineering, you can end up with this, or even a little more simple again.
Three oil lines, and maybe even down to two. Having less oil lines also reduces cost, which is good for the car owner/builder.
So here's how to do it ....
Firstly, you don't need one of those expensive three-stage external oil pumps to move the oil around. They need Gilmer belts and so on to drive them, and while you may well still want to go that way you really only need a single-stage scavenge pump for most applications.
You don't need an external pressure pump as the factory one that often sits at the front of the engine is good enough, again for virtually any application. All you have to do is change the oil feed into it from the sump to an external line. On something like the crank-mounted pump on a 4AGE it's pretty easy as they have a gallery already running up the side of the pump that you can tap into.
Not the best photo, but this is what the oil feed to the pressure pump on my racing car looks like.
There's a blanking plug on the side of the pump that you remove, and then attach a fitting for the oil line from the oil tank.
What then normally happens on most dry-sump systems is that there's a remote oil filter fitting that has two oil lines, to & from, the big oil filter. With modern filters you don't really need to do that, so I'd recommend just leaving it on the side of the block as they come from the factory. However, what I'd recommend for a lot of cars that do club work (i.e. sprints of no more than say 10 minutes or so at a time) to fit a water-to-oil intercooler between the block and the filter. Pictured below is a Subaru WRX unit, and it's very easy to fit.
All you need to do is to add two water lines, one from the cool pressure side of the water system and the return from the cooler to the hot water from the engine to the radiator. (For my new engine I am going to fabricate a small pair of alloy sleeves that go in the radiator hoses, one with a small scoop to get some of the cool water and the other a small venturi to help suck the water through the cooler back into the hot water return)
Okay, so now the oil has gone through the engine and it's time to get it to the sump and then out and back to the tank.
This is one of the cool bits of a dry-sump system, because the sump on such an engine is much more compact than a regular wet-sump one. They can be made 30mm deep on most engines, and that's a great help if you're tight for space. The other benefit of course is that even a good wet-sump will be very unreliable for getting oil to the pressure pump with lateral G's more than about 1.0 or so. All it takes is less than a second of no oil when cornering, and you've done thousands of dollars worth of damage - more than the cost of a dry-sump system!
Fortunately it's not too hard to make one. The one below is the one we ehave made up for the SR16 that's going into the Mallock. It's about 30mm deep and it's made from a standard steel sump. The bottom is cut off and an angled plate is welded on to form a shallow V, running down in this case to the right side of the engine. That's important because most of the oil tends to end up on the right side of the sump, so that's often the best place to collect it.
If you like, you can add scraper plates and so on to help get the oil off the crank. In this sump, we only have the single suction line, but a lot of people like two and there's nothing wrong with that, other than you typically need two scavenge pumps, one sucking from each end of the sump.
Here's my Fraser's sump, and it has the oil collector running down the middle of the sump and two collectors.
I can't see why you couldn't run a single scavenge pump with two collectors though.
Also most important is to have a coarse steel mesh in the sum, to stop the odd bit of broken engine go through the scavenge pump and shred it. (Even so, if the engine goes BANG you have to very carefully inspect and clean every oil line thoroughly. More than one friend has destroyed a brand-new engine because of crud in the oil lines, left over from the last blow-up)
Here's the current racing car's sump, with some off the mesh I was talking about.
Also in that photo are a couple of magnets, to try to help pick up the little bits of metal that float around.
From the sump, you then have to suck the oil out with a scavenge pump.
This can be a little tricky, and is likely to be the most expensive part off the home-made system. Virtually all of them are belt driven by a toothed Gilmer belt and there's not a lot of ways around that. So this is the setup we have on the current racing car.
As you can see, it's driven off the front of the alternator. That's a fairly easy way of doing it, though they are often setup to run on their own belt. They need an additional toothed pulley graften onto the front of the engine pulley, and that takes a little elegant engineering. No way around that unfortunately!
The oil line from the sump comes out of the front of the sump and there's a short flexible line from there to the scavenge pump, then from the pump either (typically) through an air oil cooler or directly to the oil tank.
The scavenge pump in that photo is one we made at home out of a chunk of alloy and two sets of Holden 308 oil pump gears, sitting end-to end. It's driven at about 2/3's engine speed. More on how fast to drive the pump shortly.
An off-the-shelf alternative is one like this, from BDG in Perth.
They're several hundred dollars but saves a lot of machining. (and oil leaks until you figure out how to make the damn seals work) Being a gear pump, they pump a lot of oil and so are a very good thing. Quick tip - try to orient the pump so that there is always some oil left in it, so the gears stay wet when they spin again, and so make suction. It's a pain in the arse having to prime the pump each time you want to start the engine otherwise.
To work out how fast to drive the pump isn't too hard, all you need is a lathe os some other machine that has a constant speed output. You have to get the pressure pump from the engine and time how long it takes to fill a five litre container at such-and-such an rpm, then do the same with the scavenge pump. Then you run the scavenge pump so that it pumps 50% to 100% as much more as the pressure pump - The reason for that is the scavenged oil is full of air and very frothy, and so takes up a lot more volume. The scavenge pump, to do a good job, should also create a partial vacuum inside the engine so 100% more volume is just fine. The partial vacuum also helps increase power as it helps get the oil off the crank as it spins around.
We came up with another solution that with a little patience and machining should work well - Mount the scavenge pump right on the front of the crank and spin it at engine speed. here's one we made for the Suzuki in the current racing car, and it has the troichoidal gears from two oil pumps in it, so it pumps exactly twice the oil as the pressure pump.
There's a couple of small brackets that hold it to the front of the engine, and a small fitting attaches it to the front pulley. Thus we are able to lose the extra belt otherwise needed to drive the external scavenge pump. Also, if you make the steel line(s) that come up from the sump just right, all you need is a single clamp to hold them to the scavenge pump, thus again eliminating another one or two oil lines .... and so down to a total of two.
From the scavenge pump, the oil then passes to the oil tank.
Some time ago I drew up a rough diagram of how they're supposed to look and it'll do for now.
#1 is the filler cap.
#2 is the breather. It should go to a catch-can in case of overflow.
#3 is the oil return from the scavenge pump. It comes in tangentially, to spin the oil around the inside of the tank to help de-airate it. Also cross-section 'A'.
#4 is the plate that helps stop the oil swirling and fall down into the lower half. Also cross-section 'B'. Note the large hole in the centre, and smaller holes around the sides. It's also coned a little though this isn't too important.
#5 is the oil line to the pressure pump.
The oil level with the engine off should sit about 25mm below the plate. That level should be checked not long after the engine has stopped, as quite often oil will sneak back through the scavenge pump into the sump, so leaving the oil tank looking drier than it really is.
There's no real minimum oil quantity with an oil tank, as long as is never comes close to running dry at high revs and there's enough running around for the oil cooler to work on. If the oil cooler isn't working well enough, no matter how much oil you have it'll eventually heat up too much.
The really clever systems have the entire tank sitting inside the bell housing! But they're a lot harder to maching and keep cool.
Here's another photo of my racing car engine, and it's got a few things that aren't right.
It's got a breather from the crankcase to the oil tank, and another from the cam cover. Those aren't needed, as the scavenge pump does all the breathing. On the new engine I'm building, it'll have a valve in the cam cover that maintains a preset vacuum in the engine. It's best to let the air in from the top, as the air will then travel from the top of the engine to the bottom, which helps the oil return from the head to the sump. The vacuum will be so good that for the twin-cam type engines that have the small semicircular rubber plugs in the back of the head, they have to be turned around so that the lip on one side is on the outside, or they will be sucked into the head.
Back to cooling the oil for a moment - A water-to-oil intercooler is a good thing for road cars and cars that only run for short-ish periods on the track. However, if the cooler is a good one (Setrab in-line type, etc) then they should be more than enough to do the job longer term. They also have the benefit of getting the oil warmer faster after startup, which helps reduce engine wear. The downside is that the water radiator must be able to shed the extra heat that has been added to it.
If in doubt, a conventional air-type oil cooler will be fine, but make sure it get good airflow through it.
That's all I can think of right now, more later maybe.
Hope this is of interest.