In recent articles we've spoken to industry experts about different types of
management system upgrades and airflow meters versus MAP sensors. In both
articles David Alexander of Sydney's Silverwater Automotive stressed the
importance of good tuning.
"The skills of the tuner
are vitally important, whatever the approach you take," he says.
It's all too
easy to plough your money into hardware, neglect tuning and end up with a car
that is temperamental to start, thirsty, down on power and high in emissions.
In this article we'll explore engine management tuning.
Dyno Tuning
It doesn't matter if you've opted for an interceptor, piggy-back, stand-alone
system or a factory ECU remap, there is one step that cannot be avoided - the
engine must be tuned on a dynamometer. The majority of workshops have
only the facility to tune the car on a chassis dyno, but the bulk of extensive
tuning is ideally performed in an engine dyno cell. Most people steer away from
engine dynos since the engine must be removed from the vehicle, adapters may
need to be fabricated and there are greater costs involved.
"The time it takes to tune an aftermarket stand-alone computer depends how
much base programming comes with the computer, the characteristics of the engine
and your experience with the given injectors etc," says David Alexander.
"A
MicroTech system comes with a program that should run the engine, but some of
the sophisticated ones with more parameters arrive pretty well blank - for
example, an Autronic, MoTeC or a new Wolf 3D."
This can have a considerable
effect on the time and cost involved in tuning.
"In most situations, you probably spend four hours tuning a stand-alone
system on the chassis dyno.
"Some engines may take longer if they have unusual
characteristics at certain sites.
"Engines with hand-made intake manifolds,
relocated injectors and big cams make it difficult to achieve a good result that
spans the whole way through the rev range.
"On top of that, some ECUs take a lot
of keystrokes and so take longer to tune than others. Some also lack the parameters
you need to achieve a good end result, so you end up wasting time trying to fix
it some other way."
The base mapping of fuel and ignition comes largely through experience -
knowing where an engine might need ignition advance, or where it might be safest
running rich comes from prior experimentation. Most tuners enter the initial
batch of timing values very conservatively and first focus on the amount of
fuel flowing into the engine. Ignition timing values are usually set second,
specific to a particular fuel octane and (where appropriate) boost level.
"During a typical tune the inlet air temperatures vary hugely, so you end up
with tuning across a reasonable temperature range," says David.
"Most systems
have air temperature correction, but there's more to it that that -there's the
location of the temperature sensor and all kinds of variables. I think intuition
is more important in tuning for different temperature ranges.
"In the case of an interceptor, you don't have to go back and worry about all
of these parameters. All you usually want to do is get in there to make a couple
of tweaks to the existing system - like lean the mixtures at certain sites - and
that's it. Everything else is already correct. The same goes for a remap of an
original ECU," says David. "And that saves a lot of time."
Mapping on the Road
Once the engine has been extensively tuned on a chassis dyno, is it necessary
to then hit the road to tune for real-world drivability?
"It's certainly necessary to road test the vehicle once it's been chassis
dyno tuned. I can get it running pretty right on the chassis dyno because I've
been on there for such a long time but, regardless, you still need to put it on
the road.
"There are some times when you need to do some mapping on the road at very
light throttle, trailing throttle and over-run situations - things you can't
quite simulate on the dyno.
"Decel is often included as part of an emissions test
and you can't really pull the kind of manifold vacuum on the dyno that you can
on the road. You can also get the right acceleration characteristics from those
heavy vacuum conditions and it's also easier to determine if the decel shut-off
resume might not be at the right point.
"So, yes, there are certainly times when you need to take the car out onto the
road and give the tune a tweak in those light load areas."
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How Car Manufacturers Tune Their Engines
Don't expect that a perfect tune can be achieved with only a very short time on
a chassis dyno. To put things into context, we need to consider the efforts that
car manufacturers put into mapping production engines. Literally thousands of
hours are spent making changes, numerous engines are put through torturous
durability testing and followed by extensive on-road testing. This typically
involves testing in weather extremes (snow field to the desert). These are the
lengths that must be taken to ensure a car performs in all conditions.
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Cold Start
Having done stories on countless cars with programmable management, AutoSpeed
has noticed that a very high number struggle in cold-start conditions. We asked David
Alexander about the problem.
"Well, the proper definition of cold start is a window that's only open for a
number of seconds. Once you get any heat into the combustion chamber, the cold
start environment is pretty much gone.
"You can get cold start characteristics
right through experience, but there are some engines and set-ups that are a real
challenge - factors like fuel temperature, fuel pressure, ambient temperature,
combustion chamber design and ignition timing all play a part.
"Whenever I tune a
system I always get the car until the next morning when I can go in and set the
cold start and warm-up cycle parameters.
"For sure, though, factory computers have a lot more starting maps
than any other aftermarket computer. The new Wolf system has quite a few
starting strategies these days, but even a factory system from fifteen years ago
has something like a hundred. The limitations of programmable systems is
certainly a major issue in that particular area of tuning," says David.
Factory Mapping v Aftermarket Mapping
"The car companies set their cars up to cope with every conceivable condition
that might be experienced in any part of the world. They'll also draw upon their
experiences in every part of the world and they'll enter the according data into
the ECU - it may never be accessed in the lifetime of the vehicle, but it's
always there.
"With an aftermarket system you can get very good results for what is
typically a narrower application. You can get the car so it's nice to drive on a
day to day basis, but to get things spot-on for every condition you'd have to
spend weeks playing. And in many instances you'll never be finished because of
limitations in the flexibility of the aftermarket computer. The brainpower is
relatively limited.
"Winter and summer changes in local fuel mixes can cause detonation issues if
you're tuning for absolutely ten-tenths. On the other hand, the knock-sensed
factory systems - particularly the new Subarus - with closed-loop fuelling and
timing will keep the engine running as well as it possibly can. They're really
extremely advanced."
Contact:
Silverwater Auto
+61 2 9748 1300
