Four of our six Cavs have had replacement cats in the last year in fact.
These failures have been caused by; one count of old age, two cases of rich running (1 bad O2 sensor, 1 bad knock sensor) and one failed (as far as I can tell) simply because it was an awful part fitted by the previous owner.
So I've had a few chances now to sample what's available on the market and to get things right.
First of all, it is absolutely not worth getting a cheep non-type approved part. They have hardly any substrate in them, usually very badly constructed and are way too small possibly hampering engine power.
Here is a visual comparison between a type approved part and a non type approved part both for the same car (C20NE).
These are both made by the same company; BM catalysts.
Type approved top
Non-type approved bottom
As you can see, both come with an integral heat shield and overall they look fairly similar.
Look more closely however and you begin to see differences.
The type approved part seems to be made from higher grade steel and is better constructed in general.
Here you can see the type approved part (right) has flanges that are thicker and more heavy duty:
Take a look at the welding and you'll see that the type approved part has a casing that is welded together all the way round rather than just pressed and spot welded:
They weigh differently too. These are just bathroom scales so they aren't very accurate but it gives you an idea of the difference between the two:
Non-type approved (1Kg approx.):
Type approved (2Kg approx.):
Both of these parts are advertised as weighing 2.6Kg by the way.
Now, on to the most important part of a catalytic converter, the substrate.
If the difference in weight of these two items didn't give the game away already, have a look at this:
Type approved:
Non-type approved:
Side by side:
On the non-type approved part, the substrate doesn't start until about 6.1 inches (15.5 cm) into the casing:
On the type approved it starts at about 4.5 inches (11.5 cm).
I recon the type approved part has at least twice the substrate inside.
Now this may sound like it's good right?
Well lets compare it to an original part fitted from the factory, again this is for the same car (C20NE) and holds the GM part number 25130233:
This original part is gargantuan in comparison. It weighs about 5Kg maybe more, is about twice the diameter and is packed with substrate from one end to the other.
Surely even the type approved after market part couldn't do the job as well as this could?
Now on to the second part.
Twice, in the search for a replacement cat, have I been miss-sold the wrong part by a salesman.
One, I specifically asked the seller beforehand 'is this part type approved' only for them to send me a non type approved part. When I confronted them, they said that the part I wanted was no longer available. Thanks for letting me know beforehand!
The level of customer service with most of the sellers I've dealt with was atrocious. Now I'm not saying they are all like this, I think I just got a couple of bad eggs, but it doesn't instill me with a lot of confidence in the industry.
Every time I came to a supplier with the simple question of 'Do you have this specific part available'
I was greeted with the reply of 'what's your reg no.'
This is not answering the question and is of no help to me at all, especially as the reg number alone is not enough to identify the correct part for the car I was looking for (My C16NZ2 engined LS if often mistaken for a C16NZ on many parts systems).
After trying to explain this to them I'm normally met with exactly the same response.
Another time, I ordered a part that was advertised as a BM part only for one made by ECC to turn up.
To be honest, I think this was a bit of an upgrade as it seems generally a bit nicer than the BM one above.
Note the BM part number on the packaging (90063H):
Printed on the part itself it had an ECC part number:
I measured the substrate on this as well. It has slightly different proportions to the BM part so it's not directly comparable but this gives you an idea:
So there you have it.
If you are looking for a new catalytic converter, make sure you're getting the part you ordered, make sure it's a type-approved one and ECC are slightly better than BM.
Also, if you can, get one made up for you at an exhaust specialist. It's the only way to get anywhere near OE quality.
