I bought a secondhand ninja sports cat a few years and its been ok.
Last year the mot station took a while to get it through the emissions this year they couldn't get it to go through.
Do cats wear out or loose their affect over time or is the mot station to strict?
I've had to put the standard cat on fot the mot, am I ok to drive it for a while although its been mapped for the sports cat?

Thanks guys.

 

I know nothing about this, but what I can say is the guys at EuroSpec advised against me getting a sports cat for the very reason you describe. Will be interesting to see what those with sports cats have experienced.

 

Once it's through it's mot put the sports cat back on, while your normal cat is on drive it off boost, over very little boost but don't go round with a lead foot as it will start to cause problems!

 

Thanks wiggy, thought that might be the case.

 

Sports cats need to get pretty hot before they will be effective enough to pass the mot test. When mine was tested it was 47 when i needed to be 20 or below to pass. The tester left it ticking over but it made no difference. He then revved the engine to about 3k for about a minute and it dropped to 19 and passed. He told me they are allowed to rev to 3k rpm for a max of 3 minutes for the test.