Toward the end of my last track session for 2018 I noticed a significant change in exhaust tone. I thought the larger second position OEM cat had finally failed, but it turns out it was the first smaller cat ahead of it. If you see a break like this, you should also check your motor mounts. Chances are one or more of your mounts is broken or weak, causing excessive movement of the engine. This additional rocking of the engine finds the weakest point in the exhaust and causes either the flex joint or this joint to fail.
This turns out to also be the most common cause of emissions test failures for this car. The joint fails causing a leak and then the second O2 sensor throws a code. If you’re looking at a used car to buy, check out the area circled in red below:
It can be repaired, but if you’re going to go to the trouble to pull off the manifold to weld it, you might want to consider buying a new one so you don’t have to repair it again in a couple of years when something else breaks. The stock part number is 18407566102 and it costs about $1100 to replace with OEM parts. Alternatively, you could go with an aftermarket OE style manifold which costs about half.
A third possibility is to go with a performance header and supply your own cat if you want to keep it road legal. That’s the route we’re trying. We got a Megan Racing Header along with a MagnaFlow 49-state catalytic converter and had it fabricated to match the cat-delete pipe.
MINI placed the electric power steering pump and steering rack very close to the header. If the pump ever over-heats it turns itself off. If this happens on the track (which it has to me) it can be very unsettling as the steering instantly becomes VERY heavy. So before installing the header, I decided to wrap it with DEI header wrap. This video shows how to do it.