- It doesn't matter how much power our engine makes if we can't keep the thing cool and
that's been a big consideration right from the time we decided to start this project.
Given that our original V8, initially we had a lot of trouble keeping that cool,
we're now putting a smaller capacity engine in it, albeit one that's going to be making
significantly more power.
When we make power, that creates heat, we've got to dissipate that heat so this
requires a pretty significant rethink of the cooling system in the car.
I'm talking here not just about the radiator but we've also now got to add an intercooler,
that's going in front of the radiator so that of course is going to affect the airflow
through the radiator.
We've then got our oil cooler for our engine oil as well as our transmission cooler and last
season even with the V8 we were starting to see the oil temperatures in the transmission
creep up so we want to keep those under control and make sure that's going to be
reliable.
It's also not just about getting airflow into those coolers, it's also about getting
airflow out so in this episode, we're going to go through the design strategy and the
construction of our cooling system.
- So today we're here working on the ducting for the cooling system, doing some mock ups.
I'll show you what we've got going on here.
So the first part we've started with is the inlet for the intercooler and radiator which
are stacked together.
So the general concept here is that you want to do an expansion from the inlet to the outlet
where it meets the cooler.
The idea here is when the flow's coming in, 'cause you do an expansion it slows down
and when it slows down the pressure goes up.
Just basic fluid dynamic principle and the advantage in reducing the velocity is it means
the air molecules that are in contact with the coolers spend longer in contact so they do a
better job of transferring heat.
The other advantage when you increase the pressure is that it effectively increases the
density and means more molecules are in contact with the heat exchangers which again
helps your heat transfer.
One of the other things that's important when designing a duct like this is to keep
the rate of expansion as gradual as possible.
In theory you don't want any angles greater than roughly seven degrees of expansion ratio,
that's a theoretical number, in reality it's really hard to achieve most of the time.
You can see we've got some pretty aggressive expansion on the top.
That's really just limited by packaging so at the moment the inlet for the bumper is
somewhere around here, this extends slightly past the inlet so there's just not enough room
to do an expansion as gradually as we'd like to.
There is one thing that happens, the closer you get to the cooler, the more aggressively
you tend to be able to expand and that's just due to the blockage effect.
So obviously in here the flow's pretty free but when it comes through the coolers it
essentially has a blockage and that allows you to get away with a slightly more aggressive
profile as you get closer to the coolers.
So that's what we're trying to take advantage of there.
The other thing that's important with your duct is that the front face and these inlets
here which is a little bit hard to see but essentially that's the line of the tangent
of the front of the duct is in line with the flow as it approaches the guard.
That helps again with getting everything lined up and keeping the flow attached 'cause
the last thing that you want is the air coming in and detaching and starting to tumble
because it ends up reducing the effectiveness of your heat exchanger.
This at the moment, this is a bit of a, just was a sort of first concept, I'm not sure if this is
exactly what we'll end up with.
We may try to reduce this angle a little bit more, we'll just have to see how
everything fits.
One of the other things that's really important when it comes to ducting is getting
the sealing right.
So we're trying to direct the air to go in a really specific direction here and the air will
always take its line of least resistance so what we'll end up doing in the final version
which probably initially is going to be in aluminium is running a flange 90° all the
way around with some foam seals so it can be rigidly attached to the front of the
intercooler there and that'll mean that any air that enters this duct will actually be
forced to go through the intercooler and the radiator.
I should have said before, what you see here, this is just bracing at the moment to keep the
cardboard square, these sections here won't be here, it'll be a relatively sharp edge at the
top and bottom there without these pieces of cardboard which are just there for the
mockup.
We'll also be adding seals in between the intercooler and the radiator.
That allows us to stop some direct heat transfer between then both from the
radiator to the intercooler which is obviously running, the radiator's obviously running
pretty warm having engine coolant in it.
And the next step we're looking at mocking up is the outlet duct from the back of the
radiator.
In principle it's essentially a reverse of what we had at the front.
We're going on from a large area to a small area so we're trying to recover the velocity
by going from a large duct to a small duct.
This is the shape that we're mocking up for the air outlet on the bonnet.
So the bonnet line is a little bit above the rocker cover here so this surface area here is
around about 40% of the area of the front area of the radiator so going from this
surface up to this surface means the velocity will increase and that helps draw
air through the entire system.
What we really want is a velocity on the outlet of the duct similar to the free
stream velocity of the air coming over top of the bonnet.
That's the ideal, obviously very difficult to validate that without a wind tunnel or some
CFD but that's some basic working principles of ducting for heat exchangers.
So the other thing we have to consider when bringing the duct out of the back of the
radiator here is clearing everything on the front of the engine.
So we've obviously got the oil pump drive for the dry sump.
And the water pump pulley which is just roughly mocked up here as well.
The alternator's down here but that's not really a problem because it's lower down and
these are sort of the worse case scenarios for us to have to avoid on the front of
the engine so like I said before, we want to keep these angles as gradual as possible
but just because of the space restriction here it's going to have to be a relatively aggressive
bend right out at the bottom of the radiator.
Because that's air running into a wall rather than running the other direction we can
probably get away with that without causing too many problems as opposed to if we
were trying to do it really aggressively out the top here you would end up with a
lot of separation where air coming out of the radiator wouldn't want to follow that wall.
Probably the most challenging bit that we have to fit through is running from the
outlet of the radiator core down here in this section because of the inlet pipe
and to some extend the intercooler pipe as well but we did have the guys that fab'd it,
Vinny Fab, we had them run everything hard this way as much as they could which
they've done a really good job of.
It just means that we'll have to have somewhat of a kink coming through here
which isn't ideal but that's just what we've got, that's all the room we've got so
ideally we'd be joining up with these corners to the duct but that's just not
going to be possible and it's not really worth having an aggressive bend right at the top
here to rejoin.
So I spent the rest of the afternoon getting the outlet duct for the new radiator setup done.
So the concept we've got, the same thing that we had on the inlet to the radiator.
Here we've got this duct starting at the back of the radiator and it contracts down to the
outlet.
So this area here represents the hole and the bottom of the duct that we'll have in the
bonnet but we've just got it sitting like this just because it gives a bit more
rigidity, helps it hold its shape a little bit better.
We'll add a flange to the top of the radiator and this will have a face that it will seal
against.
So my plan is to make this, we're just going to make this out of thin aluminium sheet
metal to start with.
Makes it quick to prototype and also if we need to change any geometry it's pretty
quick to cut and weld and maybe further down the track when we've got a bit more time
we'll turn these into composite instead.
I'm sure we'll have some mods we want to do to them as well.
But before the aluminium ones are ready, we are going to need to do a little bit of
clearancing so my plan is to make the duct geometry quite simple and then come in
afterwards and take out some areas where we need to.
So this is going to meet, basically like a rectangular face along the front of the
radiator but there's some areas here like where this V band clamp is going to need some
extra room.
What we'll probably end up doing is just taking that whole corner off and just using
some flat section to have a nice smooth transition but give us some clearance
to that corner.
But the larger problem is the inlet to the turbo.
So we kind of anticipated this which is why we kicked it out over this side.
It does kick over quite early but we're still going to need to take a little bit of material
out of here.
Tomorrow I will work on finding the shape for that but essentially what I think we're
going to end up with is like a pipe shape scollop through here just to give us
some clearance so this can run down through here and back original where
it was sitting originally along here.
But overall I'm pretty happy with the duct layout that we've got.
Kind of gives you an idea of the profile.
You can see how it diverges there into the front of the intercooler which will
hopefully give us some nice efficient cooling.
- So there you go, there is our design for our ducting and our cooling system.
If you've got questions on anything we've discussed there, please ask them in the
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