I haven't done mine yet as I'm still waiting for my mil spec cats to come in so I can have the lead pipes and this mod done at the same time. It appears that's the way Tbatt did it by looking at his pics.
I'm sure Fast Intentions could it, you might also check with Seb (Specialty Z). I showed him Tbatts pics and he thinks it's a great idea.

https://www.siliconeintakes.com/dsm-...ng-p-1159.html

https://www.siliconeintakes.com/dsm-...l--p-1587.html

I used two of each of these to make the resonators.

Would this make much difference if I already have 18" resonators?

I hope so because that's what I have.

I have said the drone is horrendous, sold mine after 3 weeks...everyone else says sounds great, ur either deaf or stupid..$1500 for a FI and then u have to get it modified by a muffler shop to get it acceptable,i dont get it..

I have been going back and forth with Fast Intentions to try to understand all this, and figure out how I can get s/c-compatible cats while retaining the OEM Nismo muffler. I'm embarrassed to say I still don't get it. I've crawled underneath the car with a flashlight, and this is what I think I see:

cats -> H-pipe with resonators in very back (?) -> muffler

I can't even seem to find a Nissan diagram that identifies the different sections of the exhaust. What I think Fast Intentions is telling me is this:

resonated test pipes -> lead pipes with 100-cel mil spec cats -> X-pipe with resonators -> muffler.

The lead pipes won't fit the OEM system, so you're stuck ordering the whole exhaust which I don't want to do. I want to have cats, but how do I get them downstream in the OEM H-pipe?

Please correct me if I'm not understanding this correctly!

TBatt - What did the work cost you? Also, are the ends of the resonators attached to the mufflers in any way? Was wondering about the stability of the tubes sticking out.

Thanks

Why not go with high flow catalytic test pipes? Berk, Fast Intentions, AAM, Kinetix, Z1, etc.?

I am trying to understand your requirement for no cats in the stock placement (down/test pipe), but cats needed somewhere else downstream in the exhaust.

The shop charged me by the hour so the total bill was around $300 with me supplying the parts.

Yes, the tubes are attached to the muffler so that they are supported.

High flow cats are just cats that are less restrictive, not made for supercharged engines which produce not only more exhaust gasses but at a much higher temperature. When I talked to Tony at FI he said that what they had found is that going to a HD high flow cat (the MILSPEC) and moving it further away from the stock location makes for a very reliable setup.

So, I followed his recommendation and went with the test pipes (removes the stock cats) and installed new lead pipes with the MILSPEC cats much further downstream of the exhaust but still before the H pipe section. All I can say is that it works. Loud, but it works.

That is what my system has too, 18 inch resonators in the H pipe section. What these resonators do that is very different than a pass through type resonator. A Helmholtz resonator is tuned (by length) to cancel out certain frequencies and in this case the 130-160Hz (2000-2800 rpm) drone. Works pretty well.

How to get rid of exhaust drone? Either turn up your radio or downshift!

Reviving an old thread.
I'm going the Helmholtz route for my FI exhaust. Just wondering if there are any lessons learned out there since this thread was created.
Does it matter where along the exhaust you place the chambers? Do the chambers need to be the same diameter piping as the exhaust? The equation people generally use probably assumes the same diameter pipe, I would guess.

Did you check out post #130. Tbatt gives some good info

I want to actually thank you for reviving this from the dead. I was planning to buy FI exhaust but that drone would annoy the crap out of me.

Motordyne always seemed too loud to me. But now I know about the Ark Grip so I might buy that.