Bypassed precat and easily passed MOT in the UK

[Ipswichroadster]

This was my main worry when I replaced the precat with a straight-through tubular header... would it pass the emissions test on the MOT?




I was not prepared to take the risk of leaving it in though, as too many people have stories of dead engines due to precat failure, so I went ahead.
Well, I can tell you that it did pass with flying colours, thank God!
The only thing to mention is that the engine has become slightly noisier, as I assume the precat muffled the sound somewhat. Gotta be honest though, I quite like the sound and I even added a K&N filter to make it sound slightly throatier.




Hope this helps someone, as I couldn't find this info before I did it.

[Gaz mr-s]

I'm surprised you couldn't find the info...owners have been doing it for years. The pre-cats are only for warm-up, were demanded by California (supposedly) & have no effect on emissions once the main cat heats up.

[Ardent]

Hello and welcome by the way.

[Petrus]

I'm surprised you couldn't find the info...owners have been doing it for years.

>20 years 

@Ipswichroadster  take care with the K&N as the MAF sensor does not like the filter fluid AT ALL. The issue is that it is a conductive liquid stimulating static electricity which is the basis of the filtering. Logically the sensitive air flow sensor gets confused if even marginally affected by the filter.
When cleaning the element use degreaser/petrol and let it dry well. Do NOT reapply fluid.

Do use the search function creatively because there is an overwhelming plethora of information on inlet/exhaust.
This is the latest/last thread about it, Under ´wanted´ of all things :-)
https://www.mr2roc.org/index.php?topic=73770.0
do read it to the end.