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This article was first published in 2004.
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Being as Old As Time I can remember when chassis
dynos were a rare breed - there might've been only a handful in a city of a
million people. (And that's your normal bread and butter 2WD dynos, let alone
the 4WD dyno shown here!) Normal guys simply didn't use dynos. They were for
race cars, and for those modifying their road cars who had pockets as deep as
the Marianas Trench. Back then, none of the dynos were PC-controlled, though
some could draw you a graph with a pen-type chart recorder. These days, of
course, there seem to be dynos on every street corner and a guy without dyno
charts is like someone at a nudist beach with their trousers on.
But the trouble with using a dyno to measure power
improvements is the cost - it's likely to cost you well over a hundred bucks a throw to
see how much improvement that exhaust made, to see whether those new fancy
design spark plugs did anything, or to set-up a boost control system.
And honestly, that's just too much. For that same
AUD$100 you can equip yourself with a range of instruments that lets you see with
at least as much accuracy as a typical chassis dyno whether you're going
forwards or backwards in your modifications. They won't give you the dyno sheet
to flash in front of your mates but they will show you how much improvement
you're making to your car's performance. And you can keep on using these
instruments forever - not just as a one-off...
But to do it won't you need a road that stretches
to infinity - one that also doesn't have any other traffic on it....traffic like
police cars? Nope - how fast can your car go in first gear? Sixty kilometres an
hour? Seventy? Well, without going over that speed, you can test your engine's
performance from idle to redline.
(Incidentally, we've done an article a little
similar to this one before -
Performance Testing. This is a massively revised and updated version of that July, 1999 story.)
So exactly how do you spend your hundred
bucks?
Buy a Bloody Stopwatch!
You'd think from the way in which people don't
want to use stopwatches that performance isn't really about how much TIME it
takes to accelerate from one speed to another! Basically, the stopwatch built
into most digital wristwatches is vastly under-rated as a performance measuring
device. With reasonable care, stopping and starting a hand-held stopwatch can be
carried out with a consistency of far less than 1/10th of a second - easily
enough to find any real power improvements.
Using a stopwatch to measure acceleration doesn't
even require that the speedo is accurate. If you want to compare your results
with figures gained in other cars, then of course the speedo must be correct,
but in the vast majority of cases you'll be simply comparing the performance
before and after making a modification. Unless you change the tyre diameter,
final drive ratio or some other gearing aspect, the speedo accuracy won't change
during this period.
The greatest variation in standing-start
acceleration times is caused by differing launches. A high-powered manual RWD
car (and any manual FWD or constant AWD car) is very difficult to launch
consistently. In both types of two wheel drive cars, wheelspin will occur if too
many revs are used on launch, while a constant four wheel drive car will very
easily bog down. For this reason, accurately measuring performance changes with
these cars is better done from a rolling start, eg from 20 - 100 km/h. However,
all cars with automatic transmissions lend themselves very well to consistent
0-100 km/h timing.
But as mentioned above, even if you can't go over
60 km/h, you can still get a good idea of power changes that you've made,
especially in an auto trans car.
In any type of testing where a hand-held stopwatch
is to be used, pick a flat, preferably deserted road. (Or alternatively, do your
testing in the middle of the night.) Set the watch to zero (it helps if it beeps
when started and stopped) and then rev the engine to the launch rpm. In an
automatic car, load the engine with the brakes while applying some accelerator.
Release the clutch (or brakes in an automatic car) as you press the stopwatch
and then accelerate hard past the designated speed. Prepare to press the
'stop' button as the speedo needle sweeps around, hitting the button a fraction
before you see the needle actually pass over the mark.
If you are after the most accurate figures
possible, make three or four runs in each direction. You will quickly see if the
figures form a pattern or are simply all over the place. Don't confuse timing
inaccuracies with the performance of the car changing during the testing; as the
engine heats up, power (especially in a forced induction car) will often
decline.
An example of stop watch testing was carried out
on a six cylinder EF Falcon. The automatic car recorded a 0-100 km/h time of 9.2
seconds in standard trim. With the airfilter removed, this improved to 9.1
seconds. The airfilter was then replaced and the bonnet 'popped' to the safety
catch. This let more air get to the factory intake snorkel and the time stayed
at 9.1 seconds, even with the filter back in its box. The bonnet was then
returned to its closed position and the intake snorkel to the airbox removed,
allowing the engine to breathe hot air. The 0-100 time then lengthened
considerably to 9.5 seconds. This Falcon engine is fitted with a dual-length
intake manifold that changes from long to short runners at a certain engine
speed. For the final test the intake system was permanently held in its short
runner position, resulting in a slow 9.9 second 0-100.
Each of the Falcon's test results made sense; all
were interesting and useful bits of information.
Take another test - this one done when comparing
the supposed power gains of an engine oil additive. Testing was carried out
between 40 - 80 km/h in second gear. The same stretch of road and direction of
travel was used for each test. The car was driven along at a steady 20 km/h,
then the accelerator floored. The stopwatch was then started at 40 and stopped
at 80km/h. Testing in standard form gave rolling 40-80 km/h times of 3.80, 3.82 and 3.86
seconds. Then we added the oil treatment which - amongst other things - was
claimed to give up to 15 per cent more power.
The times with the treated oil in the engine were
3.75, 3.76 and 3.79 seconds. This gives a 'before' average of 3.83 seconds and
an 'after' average of 3.77 seconds - a statistically insignificant six
one-hundredths of a second difference. Graphing the results makes this (lack of)
change very clear...
Stopwatch testing will clearly show performance
gains (or otherwise) from cold air intakes, extractors, exhausts, and chips. If
you're making modifications to your car - do it.
And the cost? We've seen digital watches with
stopwatch functions being sold for AUD$2... wow, still 98 per cent of the budget
left!
Buy a Bloody Boost Gauge!
This one obviously refers exclusively to forced
aspiration cars, but since many of you own cars with puffers (especially
turbos), we've put this in at Number Two. If you're making any performance
modifications to a turbo car and you're not using an aftermarket boost gauge,
you're simply crazy. (No cars that we've aware of run factory boost gauges with
enough calibration to make sense of anything - even the cars with factory
digital boost gauges.) There's something else important to note here - your new
gauge doesn't need to be a permanently mounted on the dash. Of course it's great
if you have one installed, but if you want to keep the price down, you can use
literally any old ugly pressure gauge that spans the right range. Just put it in
the cabin when you're doing your testing...
Pressure gauges can easily cost lots, but if
you're on a budget, look in secondhand machinery salesyards where often used
gauges are sold. Auction sites - like www.ebay.com - are also an excellent source
of used pressure gauges.... many people don't know what they're selling (and so
prices are very cheap) and the small size of the gauge keeps postage costs down.
There is simply no way that you need to spend more than AUD$20-25 on a pressure
gauge that's suitable for boost pressure testing on a car.
But what about accuracy, you ask? Well, again,
within limits it doesn't matter all that much. What is more important is
repeatability. Of course, if you buy a used 0-30 psi gauge and the lowest the
needle ever points is 5 psi, you're looking at trouble. But if the needle moves
smoothly through its range, and when you test the standard boost of your car
it's near the factory figure, then you don't have a helluva lot to be concerned
about. Popular myth has it that it's a critical difference between running 16 or
18 psi boost - but that's crap. Far more important that the actual boost figure
is the air/fuel ratio, the presence or absence of detonation, etc.
For most boost pressure testing, a gauge that goes
to about 1.5 Bar or 150 kPa or 1.5 kg/cm2 or 22 psi should be suitable. Note
that it doesn't have to have 'boost' or anything like that written on it, and if
you're using it just for test purposes neither does it have to be an
automotive-size gauge.
(Note that some normal pressure gauges will have
needle flicker problems when reading plenum chamber boost, especially in cars
with a low number of cylinders and/or a small plenum. To damp the motion of the
needle, stuff some cotton wool down the sensing hose.)
Hmm, OK, so you have a stopwatch and a boost
pressure gauge - that leaves 73 per cent of the budget left...
Watch the Output of the Oxygen Sensor
As briefly touched on above, knowing what the
air/fuel ratios are doing is very, very important to engine health. Most
dangerous is the mixtures leaning out, as this very quickly increases combustion
temps and so can melt a valve - or worse...
Without spending much money, the very best way to
do it is to monitor the output of the standard oxygen sensor. All unleaded
petrol cars use an exhaust gas oxygen sensor mounted in the exhaust flow to
sniff the composition of the exhaust gas. The most commonly used sensor
generates its own voltage output, which varies between 0-1 volt. In round terms,
if the sensor output is about 0.2 volts or less the mixture is lean, and if the
output voltage is over 0.8 volts, it is rich. However, the precise value of the
output voltage is less important than its relative value - whether it is
"richer" or "leaner" than the mid-point voltage.
Like, if you're hard on the throttle and the
output of the oxy sensor is less than 0.5V, you're in trouble.
Monitoring the sensor output can be done with a
digital multimeter, but in practice the response time of many multimeters is too
slow to keep up with mixture fluctuations. (However, a logging digital handheld
scope works superbly well with watching the oxy sensor output.) Most multimeters
are too slow because when the ECU is in closed loop mode, the air/fuel ratio
fluctuates in a rapid rich-lean-rich-lean sequence. This occurs because if the
oxygen sensor output indicates that the mixture is rich, the ECU leans it out a
little. When the mixture is a little lean, the ECU richens it. This constant
process causes a cycling of the mixtures around the stoichiometric point.
The speed of change of the oxy sensor output means
that it is easiest read on a bar-graph display, with a LED bar graph fast in
response and cheap. Ten coloured LEDs can be used, with two red LEDs indicating
lean mixtures (remember red is for danger!), 6 green LEDs showing mixtures in a
'normal' range, and 2 yellow LEDs showing rich mixtures.
If you can use a soldering iron and recognise a
bunch of electronic components (and only a small bunch at that!), you can build
your own meter that uses a row of 10 LEDs to read out what the oxy sensor is
showing. The AutoSpeed Shop
(Mixture Display)
sells a kit that costs just under AUD$15 - thousands of the design have been
sold.
Once you have installed a LED Mixture Meter on
your dashboard, it is very hard to go back to having no mixture indication at
all. You simply feel blind without it.
Hmm. So how much of the budget is left now?.... 58
per cent. And look, I ain't pissing in your pocket - with under half the budget
spent, if you've got a stopwatch, boost gauge and LED Mixture Meter - and you
use them carefully - you're way ahead of most people out there.
Waaaaaayyyy ahead.
Buy a Bloody Negative Pressure Gauge!
Boost pressure gauges measure above atmospheric,
negative pressure gauges measure below atmospheric pressure. It's pretty easy to
understand pressures above atmospheric - but what about pressures of less than
atmospheric? These are commonly and generically known as "vacuum" - but that's
deceptive, because there are lots of degrees of vacuum. So who cares about
vacuum gauges - except Grandpa towing his caravan and staring fixedly at his
vacuum gauge as he climbs every hill at 20 km/h?
The answer is: you bloody should.
Measuring pressures that are below atmospheric can
be incredibly useful, because this can give you a guide to the restrictions
occurring on the intake to the engine. Any pressure drops below atmospheric in
front of the intake runners (on a naturally aspirated engine) or the turbo
(obviously, on a turbo engine) will have a major and dramatic impact on power,
economy and responsiveness.
Basically, the higher the vacuum that you can
measure in front of the engine (or turbo), the more restrictive the intake
is.
So how do you actually measure pressures below
atmospheric? The best way is with the Dwyer Magnehelic gauges (other
manufacturers also make similar gauges but they're not nearly as common). These
gauges are incredibly sensitive to very small pressure variations (28 inches of
water is the same as just 1 psi, and even a 10 inches of water pressure drop on
the intake will have a noticeable and negative affect on power) and have superb,
clear markings and a large size. Again, these can be picked up at industrial
junk places and on www.ebay.com for
AUD$10-$20. Pick a gauge that has a range of 0-20 or 0-30 inches of water, then
if you find yourself using this gauge a lot, go for a second more sensitive
gauge (eg 0-10 inches) so you can see what's happening in more detail.
Measuring the pressure drop (ie restriction) is as
simple as using a quarter-inch rubber hose to connect the vacuum port of the
gauge to the intake system in front of the throttle butterfly and then pulling
peak power from the engine on the road.
For example, a standard 5-cylinder turbo Audi S4
had a maximum pressure drop of 32 inches of water, measured just before the
throttle body. That's pretty high, and takes into account the flow restrictions
through the intake, airbox, filter and airflow meter. Simple modifications to
the intake system reduced this substantially - the pressure drop of the intake
snorkel to the airbox was reduced from 9 inches of water to zero, for
example.
A negative pressure gauge is absolutely
vital when making intake mods - it can save you its cost in the first 5
minutes of testing. (Like, you'll find that most drop-in replacement filters do
NOTHING to reduce intake pressure drop - that's a hundred bucks saved straight
away......)
Hmmm, so far we've covered a way of measuring
actual on-road performance (the stopwatch), measuring turbo boost (boost gauge),
watching the air/fuel ratio (the Mixture Meter), and measuring intake
restriction (the negative pressure gauge). And there's still 38 per cent of the
budget left.
Buy a Bloody Decent Multimeter!
With 38 Australian dollars left, surely buying a
decent multimeter is an impossibility? Or are you supposed to burrow through some
junk heap and pull out a near new item for five bucks?
Nope - go buy the new one...
These days, digital multimeters are dirt cheap -
and often cheaper new than in secondhand shops. In an ideal world, in addition
to the normal volts-ohms-amps, you'd want frequency, duty cycle and temperature.
Frequency so that you can find those signals that alter in frequency (like the
output of some airflow meters), duty cycle so you can tell how near to flat out
your injectors are running at peak power, and temperature so you can plug in a
K-type thermocouple and read out every temp in the car - from intake air to
exhaust.
And here we are - Jaycar's QM1535 design which has
all of the above... except temp... bugger! But it's a very good meter (in fact, it's
the little brother to the multimeter I use daily) and has got current
measurement up to 10 amps, capacitance measurement (good for sorting out caps if
you're building an electronic kit), frequency, duty cycle and of course the
normals of volts and ohms.
As it so happens, on the night I am writing this
article, the meter's on special at AUD$29.95 (which would still give about ten
bucks left over from our AUD$100 budget) but I'll play fair and list that its
normal price is AUD$39.95.
Oh hell, we went two dollars over budget.
Should I go back now and change the title to: All
the Test Gear You Need for under $102....?
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More
Reading!
Many
of the instruments covered briefly in this article have been explored in much
more detail in other AutoSpeed articles. Searches under 'pressure gauges',
'negative boost', 'multimeters', 'mixture meters' and 'oxygen sensors' will give
you plenty of words and pics.
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