The scene - ChipTorque's Queensland dyno.
The car - a standard '03 Falcon XR8.
The requirement - modify the fuelling and ignition advance to provide the
best possible safe power on both normal unleaded and then premium fuels.
The outcome - relevant to anyone with a late model, highly tuned
engine....
Barry Smith has owned a good few hi-po cars over the years. Once he even had
a V8 Torana that was built to such high race specs that it ran on av-gas - and
nothing else. Which made his trip to Bathurst pretty damn' interesting - he
organised fuel dumps of the hi-octane stuff all the way along the route! But
fast forward about 20 years and he's one happy guy with his new XR8. Easy to
drive, responsive, comfortable, he said. And then insisted that I take his
bog-stock XR8 for a drive. And Barry's right - with the quad cam,
4-valves-per-cylinder, 5.4-litre, 260kW Boss engine under the bulging bonnet,
the current performance Falcon's an excellent mix of broad torque curve, sweet
revs and strong performance.
In fact, it feels like a car where the engine management is very well sorted
- and so not the sort of car likely to respond to ignition and air/fuel
mixture changes. That didn't stop ChipTorque trying, but since this was the
first XR8 with the Boss engine that they'd had in the workshop, it was brave of
them to have AutoSpeed along as well.
First, Onto the Dyno
The first step was to place the Falcon on the dyno and do a 'before' power
run. In addition to using this to measure the rear-wheel kilowatts, Lachlan
Riddel - head of ChipTorque - always uses this opportunity to inspect the
full-load air/fuel ratios (using an Autronic digital air/fuel ratio meter) and
listen to the engine (using aviation headphones and an amplified microphone
which is clipped to the block).
The outcomes were 184kW, an air/fuel ratio that above 4500 rpm plunged
rapidly down to 10:1, and a comment that there wasn't going to much possibility
of adding a lot of ignition timing - Lachlan could hear that on standard
unleaded fuel, the engine was already close to detonation.
Interceptor Install
Mechanic John Nash then installed the Xede (pronounced 'exceed'), the
company's interceptor. Developed in-house, the interceptor's functionality and
software is constantly being improved - for details on the first version, go to
"The Xede Interceptor". John used both a Falcon ECU wiring diagram and the Xede's
harness pin-outs to work out which wire connected to which. In this
implementation, the Xede intercepts the crank-angle sensor and MAP sensor ECU
inputs; by altering them, the ECU is then tricked into advancing (or retarding)
the timing and richening (or leaning) the fuel mixtures. The control of the
changes is by laptop, with alterations made in mapped form.
But the mapping was yet to happen - at this stage John was just wiring the
Xede into place. To do this he used small stainless steel crimps, which the
company has found to be quick, easy and durable in service. In addition to
intercepting the crank-angle and MAP sensor inputs, the Xede also needs power
and earth connections - all of these can be made at the factory ECU, which is
located under the bonnet. Once plugged-in, the Xede also lives under the
bonnet.
Dyno Tuning
The tuning of the Xede is carried out 'live'; that is, the car is running on
the dyno and the air/fuel ratio and ignition timing changes can be made under
load, if desired. Normally though the base
dyno run is brought up on the PC screen and some ignition timing is added to the
high load interceptor map. At this stage the car is idling and when the changes
have been made, a full-load dyno run is immediately completed. If there are any
signs of engine unhappiness the run is aborted; otherwise, the tuner looks at
how the new power curve compares with the original.
Then some more changes are made and another run is made, and so on and so
on....
For me, sitting in the back seat and looking over Lachlan Riddel's shoulder
as he performed the mapping, it didn't take long to realise that not much gain
was being made. Lachlan soon changed from doing just ignition timing to also
pulling fuel out of the top-end (at 10:1, the air/fuel ratios at full load above
about 5000 rpm were way too rich for max power), but the new dyno runs pretty
much overlaid the original. In fact, at one stage Lachlan pulled 6 degrees of
ignition timing out of the whole load range and performed a power run - just so
that he could see that in fact the Xede was working correctly! The major amount
of power that the engine immediately lost showed clearly that the interceptor
was working fine; but it also showed how timing-sensitive this engine is.
There was no 'magic bullet' to the tuning process: over many dyno runs the
tune was fine-tuned, with the results being judged on the power curve, the
measured air/fuel ratio, and the engine sounds being listened to through the
headphones. In addition, a display device that plugged into the Falcon's
diagnostic port also revealed other relevant information on how the engine was
behaving.
And so what gains were delivered? On this standard unleaded fuel, there was
effectively no change in power output over the majority of the engine's
operating range. In fact, from 2000 - 4500 rpm the change was no greater than
the variation that would be achieved on different dyno runs. However, above 5000
rpm the peak power showed an 8kW (4 per cent) improvement and the power curve
held up much more strongly - being up by 20kW (12 per cent) at 6000 rpm.
New Fuel
But what about on premium fuel? Barry Smith was not concerned which fuel he
ran the car on, so the fuel mix was upgraded. Note that since there was already
plenty of normal unleaded in the tank, the resulting mix wasn't as high in
octane as would be achieved when filling the tank from empty with the good brew.
That results in a safety margin on the street when PULP is constantly used.
With the Xede out of the tuning equation for a moment (ie the Xede was
bypassed for a 'standard' premium fuel dyno run), the engine showed that it
responded well to the improved fuel - peak power rose from 182 to 188kW (a gain
of 3 per cent) and held on far better from 5000 - 6000 rpm. In fact, the gains
made with PULP in the tank weren't that far off what was achieved with standard
unleaded and the custom Xede tune.
(Note that a Dyno Dynamics dyno was used for all this work - this type of
dyno normally shows a substantial loss between rear-wheel and flywheel
figures.)
But what could be achieved with the combination of the Xede and premium
unleaded? The answer is: a bit more. The max power was lifted about another 8kW
to 196kW, a further gain of 4 per cent. There was also a good gain at higher
revs - over the PULP power curve, the Xede tune added up to 10kW in the 5000 -
6000 rpm bracket.
Conclusion
The use of the Xede interceptor and a custom tune didn't result is any major
gain in power below about 4500 rpm. From 4500 - 5000 rpm the Xede added 4 - 8kW
(about 2 - 4 per cent) on either fuel, but above 5000 rpm the gains became
really noticeable. The best improvements were achieved using normal unleaded as
the starting point, but not surprisingly, the greatest overall power outputs
were achieved on premium fuel with an Xede tune.
The best bang for the buck was just to use premium fuel all of the time -
this gave a convincing power gain at high revs. But the Xede (AUD$1375, fitted
and tuned) showed that it could improve top-end power with either fuel in the
tank. In addition, should Barry decide to fit the extractors and exhaust that he
is considering, the Xede can be easily retuned to suit the new requirements.
So was it worth it? After he'd had the car back for a month, we asked Barry
Smith what he thought of the on-road changes. Did he notice the difference?
"Oh yes; definitely," Barry said. "The performance up high and from 3500 -
4000 rpm upwards is very notable."
However, Barry said the car does now take longer to start. (According to
ChipTorque, this is because on start-up it takes 0.82 seconds to configure the
Xede firmware before Falcon signals can be replicated. The company says it is
working on a fix for the starting delay, which applies only to Falcons.)
So there we have it: there are some power gains available on the 5.4-litre
DOHC XR8 engine from engine management changes alone.
www.chiptorque.com.au
www.xede.com.au
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The Intake?
While the XR8 was on the dyno, ChipTorque decided to perform a simple test
that they've done many times before on other cars. Firstly, they removed the
airfilter from the box and did a full-load power run, then they held the inlet
tube away from the airbox to get a completely unrestricted power curve. If in
either configuration the power leaps, then it makes sense to explore
modification options around the intake. If the power gain is only slight, then
leave it all as it is...
In the case of the XR8, the comparison was made with the car tuned with the
Xede and normal unleaded. And the power changes? Very little. With the airfilter
out of the box, you could interpret the graph to show a 4kW gain - but then
there was a noticeable dip further up the rev range. Bypassing the airbox as a
whole gave a power output back near to the curve gained with it in place!
While you can pick gains and losses off the graph, overall the factory filter
and airbox flows extremely well. In fact, just take a look at the filter to be
impressed by the aerodynamics of the design...
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