- The RP968 Porsche is one of the stand out competitors in the pro class
here at World Time Attack Challenge.
Now it's just gone out and run a 1:19.8 lap time.
This makes it the first World Time Attack car to ever go under one minute 20.
It's also the second fastest car outright around Sydney Motorsport Park.
We're here with Matt from PR Tech to find out a little bit more about what
makes this car so fast.
Now the car has been developed now for a few years, there's a lot of time,
a lot of technology and certainly a lot of money that has gone into it.
There's a lot of things that I wanna dig into here but can we start of course
with that amazing work of art, the Elmer Racing billet engine.
How instrumental has that billet engine been in the performance that
you're getting out of the 968 right now?
- It's definitely played a big part because the engine's a lot more flexible
in its power delivery.
Compared to the old engine, it's a lot stronger in the top end than the old
cast engine definitely.
- Now in terms of the power that you're producing at the moment,
could you have produced the power levels that the billet engine is making
on the original factory engine?
- Yes we definitely could have but boost would have come on a lot later
and it wouldn't have been anywhere near as driveable.
- Is this due to primarily the additional capacity?
- Yeah mostly due to that factor.
- What is the capacity on the Elmer Thor engine?
-It's four litres, the old one was 3.1
- Well that's a big change in capacity.
What sort of power levels are you running here at the moment?
- We're making about 850 horsepower at the wheels on about 1.8 bar boost.
- So realistically that's not crazy power levels, so particularly with a billet engine,
you should be able to expect relatively good reliability as well?
- Yeah definitely, they're fairly mild boost levels for a full billet engine for sure.
- And if you had the need to turn the power up further, is there more
potential in the engine and turbo package right now?
- Yeah there is definitely some head room there.
Not a huge amount though 'cause the turbo is sized for maximum flexibility
instead of outright power.
- So what is the turbo that it's running on the car?
- It's a GTX 42.
- And with that GTX 42 on a four litre engine, what sort of RPM are you seeing
full boost, or in other words, what sort of useable rev range has the car got?
- We've got full boost about 4200 RPM and a peak power of about 7500 RPM.
- And how far can you rev it through, where's the rev limiter set?
- About 8300.
- OK so particularly with that sequential transaxle in the back of the Porsche,
that's gonna give the driver a lot of flexibility in the power band?
- Oh absolutely that's the whole point of that big capacity engine is that you
can pull out of a corner in a tall gear and then run that along.
- Now the car despite the fact it clearly looks like it's got a hell of a lot of
aero downforce on it, it is still rear wheel drive, so there is some challenges
there with getting the power to the ground.
Now you're running a traction control strategy through the Emtron KV8,
but of course you also want to develop the power delivery so that you're not
really relying on the traction control, I guess kind of keeping that traction
control more as a safety backstop.
So can you talk to us about the strategies you're using in terms of boost per gear
or boost by throttle position?
- Yeah absolutely the boost is definitely mapped heavily off throttle position,
and also gear dependent.
And that's basically adjusted every session due to track conditions.
- So the gear dependent boost I mean that makes a lot of sense to most people.
Obviously you're not gonna be able to put full power to the ground at low
speed and maybe second or third gear where you don't have the benefit of that
aero downforce, so as the downforce increases, the ability to put more power
to the track increases.
But can you talk to us a little bit more about how mapping the boost relative
to the driver's foot pedal position allows the driver to modulate the torque better
and get better control of the car?
- Yeah for sure, well basically as he's winding on, say half throttle, through a
gentle sweeping corner, you may only want say 70% of the power that he
could modulate easily whereas typically with a turbo car, you can make full power
at nearly 80% throttle.
- So in general if you're not using that strategy, the power or torque delivery
versus throttle position is very non linear, that's basically what you're saying?
- Absolutely also the problem is that once they're on full boost,
as you roll out of the throttle, they tend to just keep driving forward.
So by pulling that boost aim back as you roll off 100%,
you can reduce the power easily.
- So essentially in a way you're kind of trying to make a turbocharged
engine respond to the throttle a little bit more like a naturally aspirated engine?
- Yeah that's definitely the goal.
- Now despite the fact 850 horsepower, we're not talking massive numbers there,
the car is still expected to run for a full lap or maybe even several laps,
so that's a lot of stress on the engine over a one minute 20 lap.
Are there any special strategies you're using in the Emtron KV8 in order
to provide engine protection if something goes wrong,
maybe the engine coolant temperature or intake air temperature become too high?
- The main safety that's running in that the exhaust gas temperature,
once that reaches a ceiling, I start pouring the fuel in to cool it off.
- So that's just protection around that temperature, making sure that the
engine is cooled down by that additional fuel if it's required?
- Yeah that's the point of it yes.
- OK so when the car comes back in from a session out on the track,
you're going to be looking at the data, download that data,
and inspecting it.
So can you tell us about your priorities in that data logging,
what are you looking for first and foremost?
- The first thing we're gonna check is that the boost is running as per the target.
Second of all I'm gonna watch the coolant pressure, make sure we're not having
any internal leakage around the head gasket.
And knock, I'm closely watching for knock traces as well and probably mixture
with EGTs are high as well.
Minorly is probably oil pressure, definitely check that first.
- So I think that's one thing that a lot of people kind of tend to overlook
is that it doesn't really matter how much power you're producing or how fast
the car is, in order to get those lap times, the first priority is making
sure the engine health is OK, and the engine is going to be able
to continue running.
So in terms of the knock system, are you actually running knock control
on the engine or are you just logging the data from the knock sensors?
- On this one I'm only logging the data, I haven't got active control turned on on it.
- And on E85 are you expecting that knock is an issue or is it fairly immune
to knock?
- No you can definitely still create knock on E85 for sure.
- Also in terms of the coolant pressure, so this is something we see a lot of
high boost drag engines using, at little bit less common on a circuit
application.
So can you just give us a little bit more detail around how that works,
you mentioned around the head gasket sealing, so what will that coolant pressure
sensor trace show you in your data logging?
- It will typically show if you're starting to lift the cylinder head and also if
you see it combined with knock, you can also see a trace,
that will sort of confirm that you are starting to lift that cylinder head,
you'll see little rises in that coolant pressure with the knock trace
at the same time.
- So essentially there, particularly with lifting the head you're allowing
combustion pressure to enter the cooling system, hence the pressure
trace will increase?
- That's correct, yeah.
- So finally once you've gone through and you know that the engine is healthy,
you've got a range of other sensors on the car, what are you looking for
in order to help improve the driver's lap times and also maybe improve
the chassis performance?
- The main thing I'm looking for is how closely my slip levels are following
my aim slip in the traction control.
If the traction control is working too heavily in the lower gears
I'm better off pulling some power back and then trying to apply a different
parts of the track if I can.
- So that was sort of coming back to what we were talking about earlier
where you're trying to rely on that traction control more as a safety
backstop rather than heavily using the traction control every part
of the track?
- Yeah absolutely.
- Look Matt, it's been great to get some insight into the RP968.
You've still got one more session to go although the weather is looking
a little bit marginal.
Best of luck to improve that lap time, it's already a scorching lap time
so congratulations on that and thanks for chatting.
- OK no worries, thanks.
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