Two cats in series

[kugzs]

Is there any benefit to running two cat converters in a row, in order to try and reduce emissions for a test?

thanks

[oldcorollas]

not really.... once a cat is up to temp, then as long as the mixtures are good, it will do it's job.
having a second cat to give extra catalysis will not have much effect if the first cat is in good condition.

plus it would look a bit weird seeing two cats under there? then again, there are 2 and 3 section cats which have different effects, so it depends what your levels of each testable product is?

if you can, before the test, go and stick it on an exhaust analyser and play with the timing and mixture (at the test rpm/load) and see what works best...
and find out what the limits are for your test also

[tooch]

not really.... once a cat is up to temp, then as long as the mixtures are good, it will do it's job.
having a second cat to give extra catalysis will not have much effect if the first cat is in good condition.

plus it would look a bit weird seeing two cats under there? then again, there are 2 and 3 section cats which have different effects, so it depends what your levels of each testable product is?

if you can, before the test, go and stick it on an exhaust analyser and play with the timing and mixture (at the test rpm/load) and see what works best...
and find out what the limits are for your test also

Some cars (i.e. the GT4) come with 2 cats from factory, 1 just after the stock downpipe, and the other a little further down in the mid pipe. So maybe 2 cats does have some effect?

[oldcorollas]

does if they are different cats with different functions
there ae different types of convertor catalysts.. and also pre-convertors etc...

http://auto.howstuffworks.com/catalytic-converter.htm as a start

and
http://www.bba-reman.com/cats.htm

copied from the above URL.. (it has popups)

The purpose of any catalytic converter is to reduce harmful emissions from the exhaust of a combustion engine. It accomplishes this through a combination of heat and a precious metal catalyst that causes the harmful emissions to either oxidize or reduce to safe elements in the exhaust flow. If the engine is out-of-tune and not calibrated to OEM specs, the catalytic converter's efficiency is greatly diminished and could lead to a converter failure.

The precious metal catalyst is bound to an extruded ceramic honeycomb substrate. The ceramic has hundreds of flow channels that allow the exhaust gasses to come in contact with a maximum amount of surface area where the catalyst reaction takes place. The catalyst must come in direct contact with the exhaust gasses for the reaction to take place. If the ceramic inside your converter becomes clogged or coated with carbon, lead or oil, then the converters efficiency is greatly reduced.

There are three basic types of automotive catalytic converters; Two-Way, Three-Way and Three-Way + Air. Each type uses a slightly different method and chemistry to reduce the harmful elements in exhaust emissions. Early model converters used a pelletised catalyst, but most modern converters are now designed with a free-flowing honeycomb ceramic catalyst. The type of converter required on a particular vehicle varies with model year, engine size and vehicle weight. Some vehicles even make use of more than one type of converter or a pre-converter to meet emission reduction standards.

A Two-Way converter, used on American cars between 1975 - 1980, oxidizes unburned harmful hydrocarbons and carbon monoxide into water and carbon dioxide. The first vehicles with catalytic converters had Two-Way reduction only capabilities.

A Three-Way converter is a triple purpose converter. It reduces nitrous oxides into nitrogen and oxygen. And, like the two-way converter, it oxidizes unburned harmful hydrocarbons and carbon monoxide into water and carbon dioxide.

A Three-Way + Air converter performs the same functions as the Three-Way converter. It oxidizes and reduces. The difference is the addition of secondary air between the two internal catalyst substrates that improves the oxidation capabilities of the converter. The secondary air is pumped into the middle of the converter between two separate catalyst coated ceramic substrates. The front ceramic performs the reduction and the back ceramic performs the oxidisation. Its like having two converters in one.

Each of the three types of converters mentioned above have a common need in order to function properly. Each needs to reach a minimum operating temperature before any emission reduction or oxidation takes place. This warm-up period immediately after a vehicle is started is when the catalytic converter is least efficient and the vehicle expels the most pollutants. Some vehicles employ a pre-converter in the exhaust system immediately after the manifold to help during this warm-up period. The pre-converter's small size and proximity to the engine allow it to heat up and start functioning in less time than the main converter. It also pre-heats the exhaust gasses and helps the main converter reach operating temperature sooner.

[kugzs]

so if i fail an emissions test with a good condition cat (hypothetically)
what are some ways of being able to pass the test. turn boost right down? etc etc

Also does anyone know the cost and also the limits of an emissions test in NSW?

[YelloRolla]

you're not likely to fail an emissions test.

If you want to do the test easy, go while the exhaust system is brand new. If you're still worried, get it on the dyno and have a look at the lower end emissions to make sure that it is running quite tidy.

[kugzs]

cheers jason. should have just asked you in the first place.

[cambelt]

all the epa tests that i have been to they always ask why the vehcle is tuned so lean.
D

[kugzs]

lol.

again, does anyone know how much these cost in NSW.
Im thinking that i might need to do one as i am going to be running an aftermarket ecu.

cheers