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Dirty Stuff - Part 4

Emissions testing a range of cat converters.

By Julian Edgar and Graham Pring, pics by Michael Knowling and Graham Pring

Click on pics to view larger images


We all know that cats clean up the exhaust. Punch a hole through a cat using a sharpened piece of exhaust tubing and you're not only being illegal, you're also being environmentally irresponsible. And with 3-inch (and larger) hi-flow cats around, there's no excuse for deleting a cat converter from a hi-po car. But do all cats actually work? In Australia there's presently a real 'who cares?' attitude regrading that question - but it's a thought that's likely to become more and more dominant as emissions legislation and testing both tighten.

Click for larger image

We decided to use Bell's Auto Service to test six different cat converters - and also to run an emissions test with no cat at all. To say the results were fascinating is understating the case - what would you say if we told you that some cats were literally hundreds of times better in reducing specific emissions than other cats? Not twice, or even three times as good. But no less than 235 times as good with one gas! Stunning.....

The Testing

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Again Stephen Bell made available his I/M 240 emissions test dyno for AutoSpeed's use. As discussed previously in this series, the dyno is identical to those used in the US to make sure that vehicles continue to comply with emissions standards. In order that it can do this accurately, the car is driven through a drive cycle test, with the mass of the emissions measured in grams per distance travelled. In other words, it is far more representative of real world driving that an idle (or even full load) gas analysis.

The car used as the guinea pig for the cat converter testing was Graham Pring's 1989 Suzuki Sierra SJ50 4WD. An unlikely candidate if ever there was one for performance testing, the car had some significant benefits for our purposes. Viz:

  • It has a carby motor which will not change in its tuning parameters with different exhaust/mufflers;
  • Previous testing has shown that it will not change air inlet temperatures during dyno runs, except between 32 and 34 degrees C;
  • Its carburettor is liquid cooled/heated to maintain constant temperatures;
  • The fan for the radiator is engine-driven, not temperature switched electrical, hence little change occurs to coolant temperature during running;
  • It uses a catalytic converter with no EGO sensor and therefore has no closed loop operation that might alter engine tune.

The 49.5kW engine is in good condition, with 150,000 kilometres on the odometer and still with the original catalytic converter in place.

Before testing occurred, each cat converter was brought up to temperature by some minutes of heavy load running, before the gas analyser was zero'd and the emissions test then undertaken.

The Cats

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Five cat converters were tested. All were secondhand, although the two large diameter aftermarket units had done very little work. The cats were:

  • Standard Suzuki Sierra
  • Standard Holden VR Commodore
  • Standard Nissan 200SX
  • Standard Toyota Supra Turbo
  • Aftermarket Catco 3-inch
  • Aftermarket Maremont 3-inch

The cats were all adapted to the Suzuki's exhaust, with the flanges and welding provided by Exhaust Technology.

The Results

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First up, let's look at the results achieved with just an empty pipe placed where the cat converter normally sits.









Gases No Cat I/M 240 Standard
HC (grams per mile) 1.2 0.600
CO (grams per mile) 24.44 10.00
NO (grams per mile) 1.92 1.500

Mmmm, as you can see - and no surprises here - if the Suzuki was undertaking the current I/M 240 test in order that it be tested for pass/fail status, it would have failed! Hydrocarbons were twice the standard, CO was 2.4 times the standard, and NO was over the limit too.

Click for larger image

But what about with the Suzuki cat fitted?










Gases No Cat Suzuki Cat I/M 240 Standard
HC (grams per mile) 1.2 0.47 0.600
CO (grams per mile) 24.44 12.48 10.00
NO (grams per mile) 1.92 1.29 1.500

FAIL!

Yep, even with the Suzuki cat in place, the car still failed the test through excessive Carbon Monoxide (CO). This'd be a good car to gas yourself with - when equipped with a standard but 150,000 kilometre-old cat, anyway. You can see that the Suzuki cat was certainly reducing emissions - but not enough. It's interesting to note that the Suzuki manual says, "The converter is designed to last the life of the vehicle under normal usage and when unleaded fuel is used." Mmmmmm.

Click for larger image

Next up, the Holden Commodore cat.








Gases No Cat Holden I/M 240 Standard
HC (grams per mile) 1.2 0.31

0.600

CO (grams per mile)

24.44

6.16

10.00

NO (grams per mile)

1.92

1.57

1.500

FAIL!

Yes, again the Suzuki failed the test - but only just. The NO level was indeed 'no' - just a tad too high - everything else was fine.

Click for larger image

The Nissan 200SX cat did a much better job - though still not good enough.









Gases No Cat Nissan 200SX I/M 240 Standard
HC (grams per mile)

1.2

0.038

0.600

CO (grams per mile)

24.44

1.09

10.00

NO (grams per mile)

1.92

1.65

1.500

FAIL!

But just look at the affect on the hydrocarbons!! The 200SX cat dropped them to being no less than 94 per cent lower than the test limit and 97 per cent lower than with no cat at all.... CO was only a little over a tenth of what is allowed under this standard, but the reason for the fail? NO was a little over the required level.

Click for larger image

Next was the Catco - the first of the aftermarket designs. Having done probably less than 10 kilometres of work, this was one fresh cat - and it showed.










Gases No Cat Catco I/M 240 Standard
HC (grams per mile)

1.2

0.004

0.600

CO (grams per mile)

24.44

2.29

10.00

NO (grams per mile)

1.92

1.38

1.500

PASS!

This cat converter shows just how stunning the cat-induced emissions reduction can be. HC was dropped by 99.7 per cent over having no cat, CO was down by over 90 percent, and NO was decreased by 28 per cent. And yes, the car passed the test....

Click for larger image

Then it was time for the second aftermarket 3-inch cat - the Maremont. Again with minimal kilometres under its belt, this cat worked very well.









Gases No Cat Maremont I/M 240 Standard
HC (grams per mile)

1.2

0.002

0.600

CO (grams per mile)

24.44

1.59

10.00

NO (grams per mile)

1.92

0.94

1.500

PASS!

This cat gave staggeringly low hydrocarbons - this pollutant was reduced by 99.8 per cent! CO was down by 93 percent, while NO was halved.

Click for larger image

Finally, time for another factory cat - the Supra Turbo's.










Gases No Cat Supra I/M 240 Standard
HC (grams per mile)

1.2

0.23

0.600

CO (grams per mile)

24.44

3

10.00

NO (grams per mile)

1.92

1.21

1.500

PASS!

With unknown kays on it, this cat gave acceptable results, bringing the Suzuki under the standard for all three gases.

Conclusion

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As can be seen, the difference in tailpipe emissions with the different cats in place can be extreme. Certainly, if we were in the business of making the Suzuki pass the emissions test, we'd have to be pretty damn careful which cat was selected...

And just a footnote: the 3-inch Catco converter that gave excellent emissions has been flow-bench tested with very good results (115 cfm at 3 inches of water) - so you certainly don't need a small and restrictive cat to pass an emissions test!

Contact:

Bell's Auto Service

bellauto@senet.com.au

08 8231 6211

0411 840 167

Bell's Auto is happy to do one-off emissions tests for a quite low charge.

Dirty Stuff - Part 1
Dirty Stuff - Part 2
Dirty Stuff - Part 3
Dirty Stuff - Part 5


Driving Styles

Talk to the drivers who take new cars through car manufacturers' emission compliance testing and you'll soon find that they take pride in their driving ability. Why? Cos a smooth driver who can always keep the car at the lowest load will record a lower emissions output than one who is jerky and always edging towards the higher permissible speeds. Yes, a good driver can get a car through an emissions test that a bad driver will fail.

At the end of the Suzuki test process we compared two different drivers working with the car equipped with the same cat. Bruce Robertson drove the Suzuki and then immediately afterwards, Graham Pring drove the car. And how did the emissions compare?

      I/M 240 Standard
Driver Bruce Graham

-

HC (grams per mile)

0.47

0.43

0.600

CO (grams per mile)

12.48

9.28

10.00

NO (grams per mile)

1.29

1.7

1.500

Note how Graham failed the NO test while in exactly the same car, Bruce passed it; while with CO, Bruce failed it while Graham passed it!

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