- One of the modifications we'll quite often see on racecars is the move to a dry sump
lubrication system.
In stock form the sump is referred to as a wet sump and basically all of the oil to
lubricate the engine is contained in the sump at the bottom of the engine.
This is a simple oil pickup that goes down into the sump, there's a built in pump,
normally driven off the crankshaft and then this draws the oil out of the sump and it
forces it through all of the oil galleries on the engine.
Now that lubricating oil is an essential part if you want to keep your engine intact
and in one piece.
Now that all works really well for a road going car and it's cheap to manufacture which is why
we see OE cars generally are wet sump lubrication.
On the other hand though when we take that car, start modifying it, start pounding it
around a race track and pulling in excess of 1.3, 1.4 G in corners
and under brakes for that matter, all of a sudden the wet sump system doesn't work
so well.
What happens is that the oil ends up sloshing away from the oil pickup under hard
acceleration, lateral or braking for that matter and then the oil pickup is going to
be able to draw in air instead of oil.
Now that can result very quickly in metal to metal contact between the bearing
journals and the crankshaft, or the bearing surfaces I should say and the crankshaft
journals and quickly results in destruction to your engine.
On the other hand the dry sump system addresses this by remotely mounting
a tank which contains all of the oil.
Let's go over some of the components though and we'll talk about what they are and how
they work.
We've just received all of our dry sump parts for our SR20 from Ross Performance
Parts over in Australia and the key to the whole system really starts with this billet CNC
machined alloy sump so this replaces the factory SR20 sump so one of the advantages
with a dry sump system is we can see it's relatively low profile so this actually can
allow us to mount the engine a lot lower in the car.
In our case we've got the engine mounted just about as low as we can with this sump just
about 5mm off our cross member.
Couple of other features with the sump, as we can see here, there's this o ring groove
that's machined into the sump where it contacts the engine block.
So this means that we don't need to use sealant to seal the sump to the block.
Particularly with a race engine, they tend to come apart for inspections and freshen ups
relatively often so this just makes the job a little bit easier for the engine builder,
you don't need to go through and break that seal and then reseal it again, we've got that
o ring there that is reusable.
Another aspect here we can see the scavenged pickups machined into the bottom of the sump
so these are the lowest part of the sump and these draw the oil as well as blow by gases
out of the sump and on the side of the sump we have these scavenge pickups.
So these are for an AN fitting to screw straight in.
Interestingly a little, nice little feature here is we can see that they have screens
inside them as well so these are called scavenge filters.
While we don't really want to think that our expensive new race engine could fail,
unfortunately sometimes that is part of racing and when we do have a catastrophic engine
failure with a dry sump system, you can also end up damaging your expensive dry sump
pump if parts of piston or bearing get sucked out through the scavenge stages and into
the pump itself so those little filters stop that from happening.
Next up we've got the pump itself, now this is referred to as a four stage pump.
Simply put we've got three stages, one, two, three, which are called scavenge stages.
So as we've already talked about, those suck the oil as well as the blow by gases
out of the sump.
The fourth stage which is actually at the front here, this is our pressure stage.
So this is responsible for drawing oil from the reservoir and then pumping it through
our engine.
Now there's no golden rule as to how many scavenge stages your dry sump system
has to have but this actually brings us to one of the other advantages with a dry sump
system, it's not just about improving engine reliability, done correctly it can also
improve engine power, engine performance.
By scavenging the oil and the blow by gases out of the crank case we can actually end up
creating a vacuum in the crank case.
And this has a couple of advantages, between creating that vacuum and also
scavenging out all of the oil, that means there is less oil mist in the crank case
and with a wet sump system we've got a oil mist in there that the crankshaft
has to spin through and it's actually harder to turn the crankshaft through the oil mist
so we can what is referred to as windage losses.
So getting all of that oil mist out of the crank case means that it's easier for the
crankshaft to spin, we end up with a small gain in power.
The other aspect is if we can create a vacuum inside of the sump, what it does is it creates
more of a pressure differential across the rings as we go through the intake stroke.
So this means we're less likely to see oil migrating up into the combustion chamber
during the intake stroke.
During the intake stroke we've got a low pressure inside of the combustion chamber.
So if we've got a low pressure above the piston, we've got a high pressure below
the piston, we're likely to see oil actually migrate past the rings up into the combustion
chamber, that's not good for performance and it's not good for engine reliability.
So there's the advantages of the dry sump system.
We've got a couple more bits to have a look at here.
One of the tricky parts with setting up a dry sump system is actually mounting the
pump so again Ross have done the hard work for us here, we've got this nice CNC
machined alloy plate and this is going to bolt to the turbo side of our SR20,
mounting the dry sump pump down below the exhaust manifold.
We also need to drive the pump and this is going to be driven off the snout of the
crankshaft.
Now that actually requires a little bit of work too so this is splined, this drive pulley
here is splined so it can actually move in and out in order to align the belt correctly.
Let's have a look at our front pulley here.
We're running the Mazworx ATI front damper and this is already drilled and set
up for a dry sump drive mandrill which is this little unit here.
So this bolts to the front of the crank pulley and it's got a matching drive for
our dry sump pump.
Generally what we're going to end up doing is driving our dry sump pump at half
of engine speed so the ratio between this pulley and the one on our dry sump pump
achieves that.
One problem we've got though, the Ross drive mandrill for our dry sump pump
unfortunately doesn't fit on our ATI damper.
Uses a different pitch circle for the three bolts and the little locating lip that
goes inside of it is also the wrong size.
We knew that this was going to be the situation when we ordered these parts from Ross and
of course Ross do make a matching harmonic damper which would have bolted straight up
to that drive mandrill.
Unfortunately due to our trigger system we are going to have to retain the ATI damper so we're
stuck with that, we're just going to end up modifying the Ross mandrill to suit our ATI
damper and that should be hopefully relatively plain sailing.
There's one other part to our dry sump system which is the actual reservoir, that's where our
oil sits.
So when the scavenge stages draw the oil and blow by gases out of the crank case,
they're pumped back into our reservoir which in our case in our Toyota 86 sits inside of the
passenger compartment behind and to the side of the driver so we can actually use
this for helping with our weight distribution.
Let's have a quick look at that reservoir and we'll have a look at some of the features.
Here we've got our oil reservoir and as you can see the general design of that reservoir,
they're relatively narrow but quite tall.
The idea behind this is even with a low oil level, there's always going to be oil down
the bottom near the pickup regardless of the G forces that the car's experiencing.
Let's have a look at a few of the features.
So at the top we've got a simple filler and the filler on this particular tank also includes a
dip stick so you've got an idea of the level.
We've actually got some external AN fittings welded on here so when this is installed we've
got a clear tube that runs down the side of the dry sump tank so we can get a visual idea
of the oil level without needing to take anything out of the tank.
At the top here we've got the oil return, so this is where the scavenge returns into
the tank and you can see it comes in basically on an angle along the side of the tank,
we'll talk a little bit more about why that is in a moment.
Down the bottom here we've got our oil pickup.
So obviously this is picking up oil from the lowest point.
Right at the very bottom which we can't see here, we've also got an oil drain, obviously
handy when we're doing oil changes.
Up the top we've also got a breather so this will go to a catch can which will be mounted
in the rear of the car.
Let's pull it apart and have a look at a few more of the details.
So first of all, if we look inside the top section of the dry sump tank we can see
the scavenge return goes in there and then it runs around, we've got this serrated tube.
Because each of the scavenge pickups is removing both oil as well as blow by gases,
we end up with a sort of aerated mess of oil and air getting returned to the tank.
Now one of the jobs of the dry sump reservoir or dry sump tank is to remove the air or
separate the air from the oil.
We don't want to be pumping aerated oil back through the engine, that's not going
to lubricate our engine particularly well so this is part of the process of beginning to
remove the oil from the air.
Let's have a look at the rest of it.
We've also got some internal baffling which we can remove from our tank so we can
get a better look.
So again this is just aimed at helping to remove the oil from the air, making sure
that when it gets down to the bottom, we've really only got oil available to be
pumped through the engine.
If we look into the bottom we've got our oil pickup.
Looking on the side, there's our AN fitting for our oil pickup.
You can see that's actually sitting quite a bit higher than the bottom of the tank so
this little angle pickup tube does the job of getting that right down to the very bottom so
we can pick up oil even with a very low oil level.
While a dry sump system like this could be considered an essential item at the top
levels of competition where very high G forces are being experienced, unfortunately
they do come at a price.
They also do add complexity to the installation and they're generally going to add a little
bit of additional weight over a conventional wet sump system.
It's all about understanding the pros and cons of each approach and deciding on the best
compromise for your particular project.
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