The OEM catalytic converters are connected to one-another with an aluminum bracket. This bracket is also attached to the underside of the transmission by two bolts with thick rubber bushings. A number of manufacturers of aftermarket cats & test-pipes have supporting connectors for this bracket. Fast Intentions, however, does not. When you install a Fast Intentions HFC (or RHFC, or TP), you do without this bracket, because there’s nothing to connect to. The J-shaped O2 sensor extensions are in the way.

This is the bracket. Part #20711Q: 2011 Infiniti G37 Sedan OEM Parts - Infiniti USA eStore

And here’s a picture of it on my dining room table, looking all beautiful with aluminum corrosion and rust stains from hot bolts.



Without this bracket, you’ll probably feel some added vibration at idle, which I’m guessing is more noticeable in the 6MT than the 7AT. It’s also more noticeable if you still have the OEM catback. If you have an aftermarket catback, the vibration is likely masked by everything else that’s going on.

Vibration issues aside, without the bracket and connecting bushings, there’s more stress (weight) on the cats than otherwise. I’m no mechanical engineer, but it doesn’t take much to understand the purpose of this bracket, and the risks in doing without it. Granted, the risk is probably really small, and I bet that 99% of the time, it’s a non-issue. But no matter how strong the FI welds are, they can break. It broke on Alfredo’s 6MT in December 2014. Seeing his break after only a few months spooked me, so I had my mechanic come up with a solution.

 

Here’s a picture of the final solution my mechanic came up with:



He took the bracket and cut the ends. Then he welded an L-shaped bar from one end to the other, extended beyond for a few inches. At the ends, he drilled two bolt holes:



Over on the cats, he welded two domino-sized pieces of metal on the pipe between the resonators and the cats, each with two bolt-holes to match up with the bolt-holes on the brackets. Then he welded two nuts to these little pieces of metal… because getting a wrench up on the upper side during installation is really awkward.



I was there while my mechanic did this work, and no lie… it takes some serious skills, and patience while lining things up. Personally, I think he did a great job.

 

My friend here on the forum was inspired by this work, and had his shop customize a similar solution. Here’s Liam’s custom work:



The bracket itself wasn't modified, and there's no cross-beam going from one end to the other. Instead all that was done here was some custom welding for new connecting brackets, and everything was bolted back together, pretty much the same as OEM.



There’s more simplicity to this approach, and the new parts are all steel, instead of aluminum. If I were to make any suggestion, it would be to avoid using the J-shaped extension as the contact point. That looks more fragile than welding directly to the pipe.

Anyway, I'm no engineer (again, LOL), so I really can’t say which is better… and I suspect it doesn’t really matter. The important thing is that the stress of the exhaust weight is mitigated side-to-side, and an annoying vibration is reduced.

I’ve been thinking of creating a thread about this, and when Liam wrote me today with these pics, it seemed like a good time to do it.

 

Good Idea but I like your solution rather than Liams. The J tube is there to handle exhaust gases to the O2 sensor and it does not look like it is designed to hold any amount of weight. Yours on the other hand use's the strongest point of the RHFC to brace it. Good job to your mechanic. You should send pics to FI and see if they take your advice.

 

I kind of agree, but based on nothing except conventional wisdom and no personal skills at welding.

You'd be surprised how strong a proper weld can be. But either way, I'm sure both will be checked from time to time.

 

John - Just to confirm.

Liam's G has a MT. It looks like it and unfortunately it escapes me after seeing it not too long ago. (I guess that's the first sign...)

And you and he both have the RHFCs. Again, it looks like it.

Thanks,
Sean

 

Yes, both are 6MT Sedans, and both have the Fast Intentions Resonated HFC.

Mine's a 2011 G37, and his is a 2007 G35 with a 2010+ front end conversion.

 

Thanks. I wonder what might be in store me as, you know, I have an X.

No box to check on a RHFC for an X. But there was one for the CBE. Wish I could front load a design other than the basic requirements definitions.

Sean

 

Great write-up John

We'll see how my bracket holds up over time...

 

Curious to know if any X sedans have any vibration issues on the stock exhaust. (RHFC should be Shipped tomorrow )

 

I run test pipes with the rest of the exhaust all stock. No vibrations here.

Edit: See below.

 

Ok, thanks for the info.

 

I have an x and I'm having the same vibrations with mine.

 

It's been a year and a half, and 8500 miles later... car was on the lift this morning getting a Z1 Transmission Mount installed, and it was a good opportunity to assess how this support bar is holding up.

Aside from some expected rust because of the heat, it's fine. All the welds are holding up, and the bar is still solidly connected.

 

After spending several months now with the pipes on the car without the bracket I can say there is a VERY noticeable vibration and it is annoying the hell out of me. Occurs at about 1800rpm. I WILL be finding a way to add this bracket back to the car. I'm 7AT FYI.