- There aren't too many Subaru WRXs
that can claim a 7.7 second quarter mile,
but still turn corners on the racetrack.
Andy Forrest's is certainly one of them.
Now Andy made the trip all the way from Scotland
to World Time Attack two years ago,
and unfortunately before the main event,
he suffered a drive train failure.
He's back for 2017 and he's made some massive changes
to the car.
So Andy let's start with that drive train failure
that you suffered back in 2015.
You've made some big changes to rectify that.
Can you tell us what you've done?
- Basically the standard Subaru transmission
doesn't cope too well with near on 1000 pound of torque.
So we looked at a transmission that would do two things
for us, one sort out our centre of gravity,
which on a normal Subaru is pretty bad,
but once you've got an H6 engine in,
it gets even worse.
So one sort out the centre of gravity,
and two, take the load that we were aniticipating
putting through it.
And the obvious contender was the Nissan GT-R 35.
- So the R 35 transmission is quite unique because
unlike most transmissions which sit directly off
the back of the engine,
the R 35 transmission is actually a trans axle
that sits at the rear of the car, correct?
- That's correct, it sits in the rear,
but forward bias so there's no real hangover.
So you're not bolting a whole load of weight
right to the back of the car that would give you
an oversteering car.
Most of the weight sits within 500, 600 millimetres
of the centre of gravity of the car.
- So with moving the entire weight of the transmission
rearward in the car,
what's that actually done for the weight distribution?
- Well that in combination with moving the engine back
some 600, 700 millimetres,
bolting the engine right back onto the bulkhead,
has allowed us to get the car almost 50/50.
I think we're about 51/49 at the moment.
- That's pretty impressive.
Now coupled with that, the R 35 transmission
has been well proven all around the world
to be capable of supporting 2000 plus horsepower
in a drag application so clearly more than capable
of handling what you're gonna throw at it?
- Yes it will be, we haven't gone as far as a gear set
for it yet.
We have the clutch baskets, uprated clutch plates,
all the usual bells an whistles that you upgrade
on these GT-R engines, actually at 3.5
So normally recommend them for
around about 1000 horsepower.
- Now in terms of those transmissions,
they're also a dual clutch transmission.
Which means that they're computer controlled,
essentially you've got two gear sets
and while you're in first gear for example,
second gear's already engaged,
and when you want to shift gear,
it simply disengages the clutch for first gear,
and engages the clutch for second gear,
giving very very fast shifts,
but this also requires computer control,
so how's that being handled in your car?
- We use the original GT-R GR6 transmission it's called.
The original Nissan TCU, transmission control unit,
and we interface with it using EcuTek software,
which allows us to then also communicate
with the ECU via canbus system,
and control our shift points from there.
Whether you want them automated,
whether you want them on the paddle,
whether you do or you don't want auto upshifts,
where your downshift limits are.
So you can program all that in along with clutch weights,
pressures on the clutch plates,
how hard do you want your shift.
The road car, standard GT-R road car
shifts almost seamlessly, you don't feel anything.
And they do that by pulling the engine torque back,
swapping the clutches very gently.
We do it a bit more harshly,
we're almost mimicking a dog box
but without the dog thump.
So we don't cut the power,
we just pull for example changing from three to four,
you pull in clutch four quite hard
before you let go of clutch three,
and you do it a lot faster than
the original transmission does.
So it's not as smooth but you don't want smooth
on a race car, you want that push forward.
- So the interaction here between the Syvecs
and the Nissan TCU or TCM is obviously quite important,
and there's a communication backwards and forwards
so when you request a shift,
the Nissan TCU will send a torque request through
to the Syvecs engine control unit to request
a lower torque value and then the Syvecs ECU in turn,
will cut engine torque to allow the gear change
to be completed.
How is the Syvecs actually reducing engine torque?
- I can set that, between the GR6 and the Syvecs,
I can determine how much torque it drops,
and up until about 700 pound of torque, it doesn't,
we just change gear,
and the gearbox has to deal with that.
Now you generate a bit of heat in the clutches,
but for events like this,
it can live with it,
we don't need big oil coolers or anything.
But if you were doing a circuit race,
and you were running 20 laps,
you're gonna have to ease maybe ease off those shifts.
But we just bang it through the gears with no power off.
So if you look at the g force trace on this car,
each time you change gear, you get a spike upwards,
of acceleration.
- So in terms of shift speed,
how does it compare to the speed of a dog box?
- It's a difficult one to compare
because a dog box, you have to come off the power
to release the dogs and let the next dog in,
then you've gotta come back on the power,
and if you're using a fuel cut for example,
it might be 20 milliseconds before the next cylinder's
fuelled up.
So you have to stack all these things together on a dog box.
So someone might say the shift time on a dog box
is 30 milliseconds.
They're looking at the actual movement of the dog.
But if they take the complete power off time,
so you're ramping out igniton,
or you're ramping out fuel, letting the transmission unwind
the torque so the dogs can disengage,
the dog moves then the power has to be reintroduced.
You might be up in the 70, 80 milliseconds shift time.
That's quite similar to what this will do,
70 milliseconds from one clutch starting to engage
to the other one fully disengaged.
But there's no off time.
So where you drop power for maybe 70 milliseconds
on a dog box, you actually get a little push forward
on this one as the next gear comes in.
So it's almost immaterial how long it takes to shift,
as it's just like if you have, remember old cars,
switching overdrive on,
it's effectively what it's doing.
It just changes up a gear with no lift.
- OK now in terms of the four wheel drive system,
you've retained that and that's added some complexity
because now with the H6 engine moved back
in the engine bay, you've essentially got an engine
right where a front differential really needs to be,
and you've got a really unique solution to that.
Can you talk us through the chain drive
four wheel drive system?
- That's right, we had, the engine, the steering rack,
and the front differential all wanted to be in one position.
The engine won because it was a big heavy lump
that we wanted to be sitting back and low.
So where that sat we couldn't get a differential
underneath it.
To sit that flat six engine above a differential
would screw the centre of gravity of the car.
So the solution I came up with was to mount the differential
behind the engine, so run the shaft forward from the GR6
transmission to the differential immediately
behind the engine, run the short shafts out the side,
so in line with the chassis rails,
mount sprockets, run chains forward to secondary
sprockets that are on the actual driveshafts.
- OK so those chains then drive forward,
essentially your half shafts are mounted
to the chassis driven from there,
and you've still got a proper,
a full front differential,
it's just mounted rearward in the chassis?
- That's correct yes so it's another heavy weight,
a relatively heavy weight mounted fairly far back.
- So again helping your weight distribution as well.
OK another change that we saw from 2015
when you were here is in 2015 you were running
twin turbo chargers.
Now you've gone to a single turbo
and I can't find a turbo charger in the engine bay
so talk us through that.
- Yeah I sometimes tell people it's normally aspirated
and that really screws with their brain.
It's a single turbo now, single twin scroll,
mainly for packaging reasons.
Didn't have any issue with the twin turbos,
worked really well.
And if I could've fitted twin turbos in here sensibly,
I might've kept that option.
But the turbo now sits where the passenger
feet would normally be.
So the manifolds on these cars that come off
the bottom of the engine, obviously being a flat engine,
with a dry sump system there's not a long route
round our sump to consider,
so they come fairly short primary pipes
into the passenger footwell area,
bearing in mind the engine is bolted
right into the bulkhead.
It's 50 millimetres back which is regulation for this event.
So I end up with very short headers
going into a twin scroll turbo.
- So again moving that turbo back and low down
in the chassis, another improvement
to your weight distribution as well?
- Yes that as well as dropping overall weight
in as much as if I had the turbo,
an option was to fit the turbo in front of the engine.
Quite common on the four cylinder engines.
But that would be mounting more weight up front.
I'd then have to find some route for a four inch exhaust
system over above the engine back
to past the midway point.
If you were to run a screamer pipe through the bonnet
or a full exhaust through the bonnet like drag cars do,
that would've been an option to consider.
But where I've got it now in the passenger footwell,
I end up with an exhaust, maybe 700 millimetres long.
So there is no exhaust system on the car effectively
in terms of weight.
So I've saved a lot of weight there as well.
- It makes a lot of sense.
How about the heat in the driving compartment for you?
- As long as I'm on the move it's fine.
Because the split doors on the car have an open
section at the rear and the aerodynamics of the car,
the way the vortex is set up on the side of the car,
the swirls tend to rise up the side,
and the air comes blasting in as I drive along.
I have to actually put my visor down
or shut the side window,
or anything over 50 miles an hour and I can barely
see where I'm going for the wind in the car.
So it's really cool as long as I'm moving.
As soon as I stop, the guys, if they're here in the pit lane
stick the extraction fan on and it just pulls
all the hot air out of there.
- You just touched on the aerodynamics
and obviously that's another really big change
that you've made to the car.
You've gone through and gone with a complete
redesign of the aero package with Andrew Brilliant
I understand?
- Yeah that correct, we met up with Andrew Brilliant
here in 2015 and he clearly knew what he was on about
running top cars and still running the top cars
here at the moment.
So he was the man to speak to.
He talks the same aero language as I do,
so he was interested to get involved,
keen to get involved with the car.
So he did the scanning of the car,
run it through his Cad simulation software,
aero package software.
I was adamant I want big tunnels on the back
like Under Suzuki had,
and he made it work.
Normally you don't get tunnels with a trans axle,
you just get a little diffuser, or a big diffuser.
To get real tunnels you had to build out towards the wheels.
The car was gonna be wide track anyway
so we had a lot of width of car to play with.
Conventional car that hasn't been widened this far
we'd struggle to get tunnels in.
But he managed to do as I was after
and work it from there.
- Now one of the problems that I think is often overlooked
with cars that run very high aero down force at speed,
is it actually normally results in something
of a compromise with the suspension design
because at very high speeds with such high down force
loading it tends to drop the ride height of the car.
And essentially the car can end up bottoming,
so you get a compromise where conventionally
you'd have to run the car very very high
which will affect the efficiency of the aero package,
particularly the under tray.
Or you end up running the car with very very high
spring rates, or run the car down onto the bump rubbers
at high speed to control the ride height.
You've come up with a really unconventional
solution to that problem,
can you talk us through the third spring system?
- Thirds springs are fairly common on single seater cars.
- True sorry I should say maybe in the Time Attack
and saloon car world.
- Yeah they're rarely seen in saloon cars,
cause saloon cars very rarely develop enough
down force to warrant that solution.
So we made our own system up that will work like that.
In this event we're only allowed four dampers on the car.
And I think that regulation was really meant to mean
four coil or dampers in the car.
But the wording said dampers, it didn't say spring,
so I added springs.
- So this is really a workaround to get around
the wording of the World Time Attack rules?
- I guess you could call it that, yeah.
So as far we see, springs were legal,
and we set it up with a third spring
which only acts when both wheels come up at once
or the car comes down levelly.
So it doesn't really affect your corner spring weight,
spring frequency.
So you gain on the low speed
and still support the car at high speed.
- So in real layman's terms what it allows you to do
is still run a relatively normal spring rate
to optimise essentially the mechanical grip of the car,
but that third spring comes in at high speed
where there's an aero loading which is pushing down
equally on both sides of the car, and supports the car,
is that a reasonable way of describing it?
- That's correct, that's exactly what it does.
We had an issue earlier today that one of the link bars
to the third spring bent and the car immediately
dropped I think it was like 40 millimetres at the back,
down the main straight.
So that's how much it was supporting the car at the back,
maintaining the car's attitude to the track,
and keeping the car at the right height for the track.
- Now another unconventional solution that I've spied
in there is to do with that front third spring setup.
You've got a little, an air ram I guess, air cylinder,
attached to that,
and can you just talk us through what that
is going to do once you've got it fully developed.
- The intention for that,
we kind of ran out of time chasing turbo issues
before we arrived,
that should've been automated.
And the plan was that the third spring could be preloaded
in proportion to the speed of the car,
or proportion to the square of the speed of the car.
So the down force acting on the car
would be offset by the pressure in that cylinder.
And it should keep the car close to ride height.
The aerodynamics work at the highest efficiency
at a certain ride height.
If you go above that you lose out a little bit,
if you go below it you lose out big style
'cause you can shut the air supply off.
So it's quite critical to try and maintain that height
on as many turns as possible.
- So this is something you're obviously gonna
have the ability to continue developing and working on
when you get back to Scotland?
- Yeah that'll be another knob to twiddle in the car
where I can pretty much set the ride height
as I go along.
If I need more front aero on the car,
instead of having to go in the pit lane and adjust dampers,
I can maybe just drop the ride height a little bit,
or raise the ride height if we've got issues
in the other direction.
So it should add a bit of ease to setting up the car.
- Well look Andy it's an amazing package.
I can't personally believe how much it's changed
since we saw it just two years ago in 2015.
Obviously you're still working through
some development on the car and I'm not sure
if it'll maybe even see its full potential this weekend,
but certainly it's got a lot of potential in it,
and we wish you all the best for competition tomorrow.
- OK thanks very much.
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