Stainless cat-back exhaust system
Catalytic converter damage
Stainless cat-back exhaust system
The exhaust systems on most modern cars are designed for two things; emissions control and noise reduction, neither of which are conducive to top performance. The standard back box, or muffler, is especially restrictive. The baffle design in it uses a very clever system that ducts the pressure waves through holes in baffle plates that cause the sound waves to bounce around and cancel each out. Clever, but it generates a lot of back pressure. The ideal exhaust system would be a straight tube from the exhaust manifold but this would be deafeningly loud. Performance exhausts use a different, straight through design sometimes called a cherry bomb. It is a perforated tube in a canister with the void between them packed with strands of glass fibre. This absorbs some of the noise whilst adding very little back pressure to the passage of exhaust gases.
The cherry bomb silencer
After a bit of research, I decided to take my car to MIJ Performance Exhausts in Walsall near Birmingham. You first choose how loud you want your car to sound; quiet, sporty or sports. I chose sporty and then chose a straight cut tip and left them to get on with it. The car is fitted to a lift, the old system is removed, and a new system is custom fabricated from 304 stainless steel. I picked it up two hours and £244 later and set off for home.

For the entire 80 mile journey I was thinking 'Hmm, bit loud, I'm convinced everyone's looking at me!' It was ridiculously loud! Anyhow, 200 miles later and the exhaust is a good 80% quieter. All you here now is a gorgeous throaty burble when you start the car and a nice, subtle sporty sound as you drive around - perfect! Performance wise, the car seems to have a lot more torque. There is absolutely zero lag between the gears and it's like being in a gear lower than the actual gear as you drive around, it really flies. Overall, extremely good value for money .
[A] This picture shows the start of the new system where it connects to the catalyst. You can see the very neat hanger that holds the middle box to the car via the exhaust rubbers.
[B] This picture shows the middle box. You can't quite see it in the pic but the underside of the box has 'MIJ Performance' embossed on it in raised letters.
[C] This picture shows the back box and tail pipe. Because the car runs so cleanly, there is no soot building up in the pipe so I've just masked it and sprayed some matt black in there. I asked for the pipe to be straight cut rather than the angle it actually has been but I think it does look pretty good!
Catalytic converter damage
If you've read the article on replacing the injector, you'll know that between getting the car into Nissan for diagnostic checks and the endless procrastinating while I dithered over how to reduce the fuel pressure, the car ended up running for around 5,000 miles with the misfire. It had occurred to me at that time that unburnt petrol getting into the cat could cause overheating of the catalyst's ceramic matrix that can poison it and cause it to crumble.

For a few hundred miles recently, there's been a terrible smell in the cabin that smelled like a mixture of cough mixture and burnt fuel accompanied by a bizarre flapping noise on open throttle that sounded like it was coming from both the exhaust and under the bonnet at the same time. The car was also noticeably lacking in power and the fuel economy was steadily getting worse. I self-diagnosed a duff cat and took it Nissan to be tested.

They gave me some puzzled looks as if to say 'Hmm, are you sure?' but then diagnosed a duff cat... After receiving a scary quote for £485 all fitted I booked it in. A couple of hours at Nissan on the following Saturday morning, and £481.58 lighter , I picked the car up. Apart from a slight smell of burning paint from the new exhaust section, she was back! I actually couldn't believe how loud the exhaust was because it had been completely silent with the blocked cat and it actually accelerated when I pressed the go pedal. Here are some pic's of the faulty part:
[A] This shows the damage inside the primary cat. The fuel poisoning has caused the matrix to overheat and crumble. The crumbling matrix blocked the cat and caused all the symptoms I was experiencing. I suspect the glass wool visible in the picture is wrapped around the matrix between it and the metal can to shield it from vibration.
[B] This shows the secondary cat matrix, no visible damage at all.
[C] This last pic shows the part of the exhaust that was replaced. The threaded hole between the two cat's is where the lambda sensor is screwed in.