- When it comes to designing engines, there's a lot that goes into producing
an engine that's going to be both powerful and reliable.
We're here with David Mountain, founder of Mountune.
And Mountune are no strangers to performance engines, building and designing
engines that have won championships in the likes of WRC, British touring cars,
world touring cars and rallycross.
And we're here to find out a little bit about their World Rallycross engine.
So for a start David, the World Rallycross engine, I mean in outright power numbers
it's certainly not the most powerful engine in the world, can you tell us what sort of
power level these engines are producing?
- OK they're all around 600 horsepower.
The reason why they're only 600 is because the regulation states we have to have a
45 millimetre air restrictor fitted to the turbo so in terms of power it's controlled
by the mass air flow.
But torque, where we can put the boost in at the bottom end, 850 newton metres
of torque isn't uncommon.
- Now just going back to that restrictor, so essentially this is a concept that's
been used in rallying for decades and it's a levelling aspect so regardless of the
manufacturer of the engine, regardless how clever the person is on the
computer keyboard doing the tuning, that restrictor limits the airflow
so that's the idea of trying to get all of the engines producing similar power numbers?
Exactly right, it's a very old system that's been around certainly as long as I have.
The great thing about it is it's very easily checked by scrutineer.
There's a no go gauge effectively so if it's the right size hole and basically it's
very simple.
So it's all about trying to get the biggest bang for your pound of air flow consumption.
So it's about efficiency really.
But it's a great way of levelling power.
Now the thing that's important to understand with that restrictor as well and you've sort
of touched on this, you mentioned that you may only be making 600 horsepower
but the torque is actually quite impressive with these engines so where the
restrictor sort of starts clamping down on the air flow is more in the higher RPM
range is that fair?
- Exactly right so if you look at where we make peak power, we make peak power
at about 6500 RPM so where the restrictor is not limiting the airflow,
we can put the boost pressure in and then very rapidly we have to decrease
the boost pressure, otherwise we'll overspeed the turbo and that then puts
the turbine back pressure up which then causes detonation and all those things.
- So boost control on these engines is really critical.
- Absolutely critical yeah.
- And what sort of boost pressure are you using down at that low RPM range
where you're not airflow restricted through the restrictor?
- We're using around 3 bar at the bottom end and that drops quite rapidly to
around about a bar at the top end.
- Now when you've got an engine like this that on face value we look at the numbers
and we see everything in magazines with what engines are producing,
600 horsepower these days we're seeing road cars making this sort of power
quite easily so on face value, it doesn't sound like it's that difficult but can
you talk to us about why that low RPM torque actually makes it really hard to
get good reliability out of the engine?
- Yeah well I mean we end up with cylinder pressures of, we've seen as high as
250 bar so we're talking about high performance diesel engine type
cylinder pressures.
So the Achilles heel has always been the head joints because our cylinder
pressures are so high.
- So when you're saying the head joint there what you're talking about is that
interface between the engine block and the cylinder head,
in other words head gasket integrity, holding the cylinder head on the
engine and holding all of that pressure in the cylinder?
- That's exactly right because every time the engine fires, if you were to put a load
cell across the cylinder head and block, it's bouncing like this.
And you've just got to keep the seal and that's why we use a very flexible
head gasket that's like a spring and it's moving with the head all the time.
And the minute you get any leakage it's game over very very quickly.
We're talking in terms of seconds.
- Now I think it's really easy for those who aren't operating at this level to look at a
cylinder head or an engine block sitting on a workbench and obviously it's nice
and rigid and strong sitting there but as you've mentioned there it's,
you don't take into account the fact that these components are actually flexing under
that high level of pressure.
Now coming from a drag racing background myself, this, as you say, is always the
Achilles heel of the engine.
How much boost we can run into it comes down to how well we can hold the cylinder
head on it.
And there are a huge range of technologies available from stainless o rings to gas
filled o rings.
You've basically suggested there you're using what sounds like a relatively
conventional multi layer steel head gasket, is that correct?
- It is, we've tried, over the years we've tried Cooper o rings, we've tried Wills
rings, beryllium rings, all of these things and actually the best compromise
we found is a multi layer steel head gasket.
But there's an awful lot of technology.
We work with ElringKlinger who, German company, and they make high performance
gaskets for a lot of the OEs and they have a small department that does prototype
gaskets and we've just found that it's the best, gives us the best solution.
- So you're not clearly talking about your typical factory replacement MLS gasket
from your local part supplier, this is a very specialist piece of equipment?
- It's a very specialist piece of equipment that's very expensive.
A typical figure of around $300 for a head gasket and we have to buy a quantity
and we have to pay for the tooling, there's a lot that goes into the head
gasket, massive amount.
- Alright so the head gasket though really is only one part of the whole strategy of
getting the head and block to seal and I think again this is an area that's easy
to overlook.
Difficult when you're dealing with OE castings because it is what it is but
particularly aspects such as the way the head studs or bolts are located in the block,
and the thickness of the deck surface of both the block and the head can play
a factor.
Can you talk to us a little bit about how you've dealt with those problems
and overcome them?
- Yes you're absolutely right it's the structure of the whole thing assembled and clamped
up which is important.
So if you try and increase the clamp load too much and you've got an OE head
casting you start collapsing the head pillars, then you lose the clamp load.
So if we're using OE heads and blocks, we have to start off by understanding
how strong is that structure, what can we do to improve it?
Typically we'll try and get a longer stud down into the block, if there's material
to do it.
Typically a slightly larger diameter if we can so we can increase the clamp load.
But then we do tests on what the whole integrity is to see at which point does
the thread start pulling from the block, does the pillar start collapsing?
And it's that whole balancing act.
- So I think again just relating this back to our street car market,
it's very common for people when they're building a slightly modified engine to
buy and off the shelf set of head studs to replace the factory bolts and torque
them up a little bit more and you think everything's fine but basically what you're
saying there is you can actually be creating as many problems as you're solving by
using more clamping force?
- 100% if you take an OE engine, the OEs spend a lot of money developing
their head bolts and they're often now stretch bolts so they go to a certain yield.
And quite often you can put a bolt in there that in effect is too solid.
When it goes through a heat cycle then you lose your clamp load.
So there's a lot more to it than just fitting a stud in and clamping it down.
- Alright so once you've actually got an engine that's capable of handling that
cylinder pressure and is reliable, really it still comes down to the turbocharger,
that's really the part of the puzzle that's creating the air flow and that's central
to the performance of any turbocharged engine.
So one the World Rallycross engines, you're not running a sort of turbo
that we could buy off the shelf, this is a very specialist turbocharger
developed specifically for the application.
Can you talk to us about that turbo?
- Yeah it's really a truly remarkable piece of kit.
I think I mentioned to you earlier if I go back some years when we
started in World Rallycross, or it was called Group A rally cars back in those days,
we had to use modified standard production turbos and it was not uncommon to
have to change a turbo at the end of each day.
So you had to cart around your spare turbo in the car, those were the regulations.
And then we finally bit the bullet and we went to a proper racing turbo made
by Garrett in the U.S. and it was a complete game changer.
We could do multiple rallies on one turbo.
Specially developed materials for high temperatures, high speeds and the guys,
just a fabulous job.
It's not cheap but in the long run it is actually.
- The other thing with these, it's a TR30R from what I understand and these are
again while you say TR30R, this is really a family of turbochargers so you work
with Garrett to develop the specification of turbocharger to give you the response
and power that you want for the particular application?
- That's absolutely correct yeah it's a family that has a wide range.
So we work with the engineers at Garrett in terms of what we need,
in terms of a compressor map and airflow to suit the actual requirement.
And they've got such a database now, they pretty quickly tune into what we need.
- Now I think another thing that's important to point out, we don't really consider this
in the enthusiast market but the weight of all of the components is obviously critical.
And that TR30R, because it's a motorsport only turbocharger, Garrett don't need
to meet OE burst retainment regulations so all of the castings, very very thin,
very very light so it's a huge weight saving?
- Absolutely, in world class motorsport like world rally car for instance,
people pay money to save weight and you're exactly right, special materials
to save weight.
But yeah we don't have the burst containment and someone in the
company's going to have to sign that off.
So there's no liabilities that come back but they are so, if you run them within
the spec they're very very reliable.
- Now the other aspect that you can't overlook on this engine because it's
right there in front of your face is the antilag system.
So we've seen a lot of ways that antilag can be used and in the easiest way,
the way we see in Group N rallying that I've been involved with in the past.
We simply crack the throttle body open, that bypasses air through the engine,
we add fuel, we retard the timing and we get the combustion event happening much
later in the engine cycle to provide energy to the turbocharger to spool it.
But you've got a much much more complex take on that with a fresh air valve.
Can you just talk us through that system and how that works?
- Yeah I mean we started off with exactly what you described.
Early days of antilag was exactly that, bypassing the inlet side and what we
found was the more aggressive we needed to make the system, basically we had zero
engine braking, lots of push on, drivers didn't like it so we started to
develop what we now call a fresh air system where we're actually pumping
compressed air into the exhaust and it gets really neat when you've got direct
fuel injection because then you can put fuel into the exhaust on the exhaust stroke,
you have a lot more control.
So effectively we can make the system very, in fact almost too aggressive if we want
it to be and not lose our engine braking.
- I'll just come back to that because a lot of people watching may not understand
what you're talking about when you say push and just to reiterate there,
so essentially with the conventional antilag system that I was talking about,
if you want to make it more aggressive, you open the throttle further,
that bypasses more air but of course we're combusting some of that fuel and air still
in the engine and it creates power.
So essentially when the driver gets off the throttle, the car is actually still trying to
drive forward and that's what you mentioned or you were talking about
when you say push?
- That's what I mean by push on.
So the driver's coming into a corner, lifts off the throttle, expects to have quite
rightly a certain amount of engine braking, hasn't got any, he's harder on the brakes,
so the brakes wear out more quickly and it, particularly on circuit racing,
it's very difficult.
- Now with that system, can you give us some numbers around what sort of boost
pressure you're seeing pre throttle body.
Now admittedly when you're off the throttle or the driver's off the throttle,
you've still got the throttle body closed so you're not necessarily seeing positive
boost pressure in the inlet manifold but I think that's the part people overlook.
You've still got positive boost pressure pre throttle body so that turbo's spooled
ready to go as soon as the throttle's cracked again.
So can you give us some numbers around that?
- Typically now, particularly if we're talking about the latest DI engines with fresh air
if you look at the turbo speed relative to throttle angle, stays pretty constant.
So even at idle you've certainly got well over 100,000 RPM turbo speed.
So you're dead right, your turbo's spooled up ready to go and the minute you crack
the throttle it's there.
So it's a big difference.
- And I think I'll just come back as well and talk about that DI, the aspect there that's
important with a conventional port injected engine we really are injecting the fuel
and it's going into the cylinder when the intake valves are open so it's being
introduced to the cylinder during the intake stroke but of course with direct injection,
you can place that injection event anywhere in the engine cycle so I'm guessing you're
basically placing it during the exhaust stroke?
- Exactly right yeah so we're putting fresh air into the exhaust manifold,
we're putting fuel into the exhaust manifold and that's it.
- Complete control over the antilag system.
- We're kind of running the turbo like a gas turbine really and coupling the
two together.
The difference, if you go in a car with a professional driver and you switch
the antilag on and off, it's just an amazing difference.
- Now we'll switch across to the other side of the engine, on the inlet manifold
there's a couple of things that I just wanted to talk about and the first is the design
of the plenum in the intake manifold itself.
You've got a drive by wire throttle body that's mounted quite low and it's just interesting
the way you're introducing air into the body of the plenum chamber itself.
A little unconventional compared to some of the factory plenum designs we see.
Where are the advantages in that design?
- Yeah well particularly with rallycross where you can either use port throttles but you
have to have a throttle cable, or you can have a single fly by wire throttle.
And there's, if we didn't have the antilag so well developed we would still be
really stuck on port throttles because you get very good throttle response,
you get the boost building up against the back of the butterfly, the butterflies are
close to the valve, you get very very good throttle response.
But you're limited to a throttle cable.
With the fly by wire throttle, you can play tunes with what the throttle's doing
relative to the driver's pedal.
And because the antilag system works so well we manage the throttle response.
- So just for those viewing who haven't heard that term, when you're saying port
throttles, really you're talking about what we'd refer to as individual throttle bodies
but the regulations there state individual throttle bodies must be cable, single throttle
drive by wire?
- That's exactly correct yeah.
- Alright the other aspect there is you've got dual injectors per inlet runner.
So I'm guessing you're running some sort of staged injection strategy there?
- Yes on the PFI engines we tend to use two injectors per cylinder because we just need
the fuel flow and we get better performance by basically running one injector at
relatively low engine power outputs and we bring the second injector in at a higher
boost level.
We just get a better spread of power basically.
- Alright now just talking about the oiling system on these engines,
generally when we look at rally cars operating on gravel the amount of
lateral load that they can generate can be a little bit less than what we'd expect
to see in a circuit car for example.
Is the oiling system on a World Rallycross engine similar to rallying or given that
they're operating on both tarmac and gravel dirt, do you go with a more circuit orientated
oiling system?
- Well a lot of this is driven by regulations.
Rallycross we use dry sump oil systems and in relatively recent years we've been
allowed to use dry sump in rallying.
In some forms of touring car like British touring car, the regulations state we still
have to use wet sumps.
And there's a big challenge with the wet sump and I've stated for a long time that I
think it actually would be cheaper to allow us to use dry sump.
- Sometimes those cost savings actually end up to be more of a larger cost
than they're intended?
- Like losing an engine because of oil surge.
- No one wants that.
Look David it's been great to get some insight into what goes into a World Rallycross
engine, thanks for your time there.
If people want to find out more about what you do at Mountune,
how can they reach out?
- The best thing's go on our website which is mountune.com and have a look.
- Thanks a lot.
- Thanks a lot, thank you.
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