P38A Cat question

I have a question about cats. Not the animal but the exhaust gas conversion system fitted to my 4.0 1999 V8 p38. Chassisnumber is something like XA415...

I have read that there are two types of cats for the V8, one for the GEMS and one for the Bosch engine. Main difference being that the GEMS system accommodates one O2 sensor per bank and the Bosch systems has room for 2 sensors per bank (one before and one after each cat).

Now my car has only the sensors before the cats fitted, not the ones after the cats but is a Bosch engine.

Can I fit the cats from a GEMS engine to mine without issue? There's a price difference + for the GEMS you can get a split y-pipe style system which means you don't have to remove the transmission crossmember. Which is certainly appealing to me.

The parts catalog gives WCD105350 as the parts number for my car, being the one with 4 O2 sensor bungs in total. It gives WCD000860 for the pre XA410.. vin cars, with the GEMS V8.

What to do?

Pre and Post CAT 02 sensors (4 total) were only for Japan and North American Spec vehicles. Most of the rest of the world got only pre CAT 02 sensors (2 total) so yours is correct. Australia and New Zealand I think got none!

Regardless of number fitted, the GEMS has a different type of sensor to the THOR, and also a different hole size for the sensors themselves. (12mm for GEMS and 18mm for THOR I think). GEMS engine management runs the 02 feedback from 0v to 5v and THOR runs from 0v to 1v (I think, I might have that backwards) so they are not interchangable.

You just need to get a pair of CATs for a post 1998 car. Most cheaper pipes come with 4 holes, but also 2 bungs so you can seal up the holes you don't need. On top of that, some CATs you can buy are "Type Approved".... this is some sort of certification to prove the performance of the CATs that you might need to pass an MOT emissions test in your country. Of course, they also charge more for them!

I fitted these to my GEMS. No good to you I'm afraid, but they were cheap, have gone on okay, and the MOT tester was very happy with my emissions test the last time so I'm happy with them!