OEM cats and Invidia Gemini possible issue

[MtJavnk]

Hi there. 
after doing some research I’ll disclose information regarding an issue I’ve been following on my car 350Z HR with OEM Nissan cats and Invidia Gemini (version 1), with 57.000km now (mileage is correct). Grab a cold drink, it’s going to be a longer post. 
 

After I’ve put Gemini on my car, I started noticing a light rattle on LH side of the car. At first it was so subtle I convinced myself it’s the infamous 350Z transmission. But later on the noise became more and more apparent and louder. Eventually I went under the car, hit the Cat with my hand and it was rattling. While figuring out what to do, the miles were going by. With miles the RH side cat started to rattle. Now it is a friggin’ silverware simphony going on. And it’s the cats. It’s not the transmission, it’s not the heatshields. 
 

Now, Invidia’s Gemini was first released with flex pipe at the flange that connects to the cat. But as this flex pipes were constantly tearing and failing, they later decided they will go the slip-on route, like you can see on motorcycles and their exhausts. With doing so, the whole exhaust doesn’t have s single flex point, stress release point. The only movement is the movement let by rubber hangers. So basicly all the vibrations are translated to the cat. 
 

This leads me to believe (asumption), the exhaust is bringing a lot of pressure, vibration and stress to the cats, which are attached solidly, on mounts, twisting and pulling the car, making the lower part of the cat’s core detach and rattle. Resulting in a failing cat eventually, presenting core shatter damage risk to the rest of the car’s core, whole lenght of exhaust and maybe even the engine. 
 

at this point I would like to ask users around here if they have had this or similar issue with nissan’s oem cats? And what exhausts were installed?

 

I am NOT amused by having these cats rattling as I know it’s another PITA job to do, not to mention the incredible expense going OEM route (2.500 bucks for a pair of new ones) or Berk (and other) alternatives which make the engine sound even louder, raspy and essentially destroying the nice VQ sound. 
 

I will email Invidia regarding this matter to get an answer from them also, but I believe (my opinion based on ibservations) they are well aware of the decision they’ve made and technical shortcomings. They have solved the RMA cases for flex pipes. And for sure they’re not paying for new cats to the customers also …

Edited March 23, 2023 by MtJavnk
Grammar mistakes

[Jack94]

Can't comment on the OEM cats (I had torqen HFCs) but I had this invidia system on my 350z for over 4 years (roughly 22,000 miles) and had no issues whatsoever. 

Edited March 23, 2023 by Jack94

[Coz@TORQEN]

Definitely sounds like the cat material inside of them is broken, causing it to rattle loosely inside, nothing to do with the Invidia Gemini, more so to do with the age and use of the OEM cats.

 

It's a very common issue on 350z's, especially as they get older.

 

That being said the HFC don't cause much drone whatsoever, most are 200 cell vs the OEM 600 cell. 

[MtJavnk]

I thought I'll post some feedback.

Thank you, Torqen. I might as well add a bit of a info here which can be valuable to other readers also. You are right, secondary catalytic core is (most probably) dislodged. It might be broken but usually it's the inner core that gets loose and eventually breaks. I wasn't aware this was also apparent on HR models. From reliable source I got the info that even with primary cores only, the car pass MOT inspections. There's no CEL light as O2 sensor is located just after primary cats. Secondary cats were later added just to keep the car EURO4. I've seen a cat from older 350Z and it's like the whole core is just being thrown around in the chamber. When you leave it long enough it turn sideways.

So, I considered just throwing the secondary core out, but was advised an empty chamber is not a good idea as it causes turbulent flow of exhaust gasses. Of course it also changes the sound of the car. After market HFC's don't produce sound I would want so I am considering buying a catalytic mat, which is used to damped the vibrations in cats and DPF filters. I'll try and wrap the core into the mat and weld it back together. Hopefully it will keep the cat in place and rattle will go away. Anyone tried this before?

 

I am suprised this happened as the car has original 57.000 kilometers.

 

[davey_83]

My car has always had a y pipe with a flexi, and the driver side second cat (the unit has two cats) is loose and rattled at certain revs or when I turned the engine off. I can hold the unit and tilt it one way or the other and you can hear/feel the core slide inside. I had planned to drill a small pilot hole and screw a small stainless self tapper from the underside to hold the core steady which would sort my problem. 

Edited March 30, 2023 by davey_83