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Dirty Stuff - Part 3

Emissions testing a modified V8.

by Julian Edgar

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Over the last few weeks we've seen how Bell's Auto Service's emission test equipment works, and the extraordinarily good results obtained when testing a Honda Odyssey V6. But now its time to get down and get real dirty with a modified car....

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AutoSpeed contributor Graham Pring's Cobra replica runs a modified 5-litre Holden V8 under the control of a GM-Delco ECU. The management software is tuned using a Kalmaker program, which makes the standard Electronic Control Unit lap-top programmable. Dave Bennet big valve alloy heads are used together with a Peter Michaels carby-style inlet manifold, equipped with Magna injectors mounted with JD Camira adaptors. The Speco cam has an inlet duration of 214 degrees and the exhaust duration is 224 degrees (both at 50 thou lift). Maximum lift is 500 thou. On top of the inlet manifold sits a MoTeC 1000 cfm quad throttle body. No cat converters are used and the car is fuelled with premium unleaded. This combination has seen a maximum power of 152kW at the wheels.

The mapping was originally done by a chip company that will remain nameless: Graham comments now that he thinks they didn't have much idea of what they were doing... He has since fiddled extensively with the program, making numerous changes to improve drivability. At times he has fitted the car with an Autronic air/fuel ratio meter - when measured in this way, mixtures have never been dangerously lean or stupidly rich.

In short, the Cobra's probably a typical example of a car fitted with programmable management and tuned a bit by dyno, a bit by ear, and a bit on the road with an air/fuel ratio meter.

Testing

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Testing of the Cobra very soon showed that the emissions were appallingly bad. Unfortunately, the test software over-writes the first test once more than three tests have been done, so a record of the first test results doesn't exist. However, memory suggests that the second test results that are shown here (they were conducted after some management mapping changes had been made) more than halved some of the emissions. And when you see how bad even the second tests results were, you can only imagine how woeful the first were!



Emissions

Cobra replica

Composite Standard

HC (grams per mile)

1.322

0.600

CO (grams per mile)

116.576

10.00

NO (grams per mile)

2.438

1.500

Fuel Economy (l/100km)

27

-

As can be seen, HC emissions were over twice the standard; the CO reading was nearly 12 times the standard; and NO was 1.6 times the standard. After the first test, the air/fuel ratio was leaned-out at rpm between 1000 - 2000, the area in which the automatic transmission Cobra was working during nearly all of the cycle. This change resulted in the improved data that is shown here. Changes to ignition timing were also made, with NO responding but CO and HC remaining at their very high levels.

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The first step in trying to obtain satisfactory emissions would be to fit cat converters, so only a limited amount of time was spent making tuning alterations. However, the feeling amongst those present was that the inlet manifold/camshaft/exhaust combination was probably going to make passing an emissions test quite difficult, whatever fiddles with the mapping were made.

Another Comparo

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While last week's ultra-clean Honda Odyssey LEV showed how good modern cars can be, what about the emissions performance of something a bit older? The test results (below) of an early Nineties EFI Mazda 323 Astina shows that its emissions were both vastly better than the Cobra, and well within the standard. Of course, we're comparing a standard car with a car heavily modified and wearing a mix of aftermarket bits and pieces, but again it shows how bad the Cobra (in its current form) really is.








Emissions

Cobra replica

Mazda 323 Astina

Composite Standard

HC (grams per mile)

1.322

0.159

0.600

CO (grams per mile)

116.576

2.962

10.00

NO (grams per mile)

2.438

0.812

1.500

Fuel Economy (l/100km)

27

7.2

-

Next, we hope to bring you the results of testing different cats and making simple, large, changes to timing and the mixtures.

Dirty Stuff - Part 1
Dirty Stuff - Part 2
Dirty Stuff - Part 4
Dirty Stuff - Part 5

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