I have a Nismo exhaust, and I love the look and sound. However, with high flow cats I just can't stand the droning on the freeway. What do you all think about the idea of modifying the Nismo exhaust by adding an additional resonator can in the midpipe, or perhaps replacing the existing resonator can with a more substantial unit that would be quieter? Do you think this would be effective at reducing the droning?

My only other option is putting the stock exhaust back on with an aftermarket y-pipe. This would flow just fine and be very quiet, but the Nismo muffler and tips are just *so* much better looking. I'd really like to keep it if you guys think it's possible to quiet it down.

 

in my research/experience (i modified my injen SES by adding an x-pipe) there's really no way of removing drone completely from a free-flowing exhaust system, without modifying pipe diameter. The only way to do so is to introduce so much restriction into the system that the resonate sound waves are redirected or cancelled out; but if you do that, then why use an aftermarket system at all?

what CAN be done though, is moving the drone to a different RPM, or "mellowing" it out slightly. A resonator alone will not remove drone (unless it's louvered)... it can only have one of the following effects:

1) Deepen exhaust note (typically achieved via a long, medium diameter canister)

2) Shorten droning RPM range (typically achieved via a large diameter canister)

The effects above are not all encompassing, and combining resonator dimensions can achieve a combination of effects. I'm not mentioning specific diameters/lengths because it differs depending on the desired result. For many, resonators are great at removing rasp. For that purpose, any resonator of decent volume will do that since the higher frequency sound waves get absorbed or cancelled out by the reosonator packing/design (depending on if the resonator works on the reflective principle or absorption principle).

If you are not happy with a deep sound, then my advice would be to remove the relatively small nismo resonator, and change it out for a short but large in diameter (6 inches or more) resonator/muffler. This will cancel out some of the deeper frequencies in the exhaust note, while mellowing out the sound ever so slightly.

If any of my explanations don't make sense (which is probably the case) the best way to think of how a resonator works is by comparing it to a musical instrument. Why does a trobone sound deep? why is a trumpet high pitched and loud but not deep?

The larger the diameter of the resonator/muffler, the deeper it will be.

(btw, one way to fix the system completely is to use a loveured resonator - but I won't get into that since it introduces signficant back-pressure)

 

I love stock exhaust + high flow CATS sound......there is no other sounds can't be compared,

 

Strife350z, thanks for the ideas. What you're saying does make sense. I guess if I could *move* the drone area down lower or up higher, that would be okay. The problem right now is that it drones right around the 3k (a little above and below), which is right where you sit when cruising on the freeway. Droning at 2k or 4k would be acceptable, but the 3k area just kills me on long road trips.

But StarcraftBW's suggestion is one that I will likely end up with. I initially had high flows on my stock exhaust, and it was great. I plan to do all the N/A mods available in the long run, so maybe the stock exhaust (with an aftermarket y-pipe) is just the best way for me to go with high flows.

 

That is great to know... because I was contemplating on whether or not to get an aftermarket exhaust??? I wanted to increase flow, but it's not worth obnoxious rasp or drown! I already bought headers and HF cats, so I can't turn back now. My guess was almost all aftermarket exhaust will increase sound tremendously and stock would be...well stock. So at least I could reduce the sound somewhat while not having to spend and extra grand trying to do it. I believe the only system that would help me would be the Greddy or EVO? Can't remember, but one of the two has large cans to help reduce noise while increasing flow. I really wanted to get the TD Borla or Stillen system, but I'm afraid with an intake, plenum spacer, headers and HF cats, the sound is going to be very, very loud! I don't know, I think the stock exhaust is pretty nice for what it is...best stock exhaust I've ever owned

 

Let me ask you guys a question since you're on the subject. I just installed headers and cats to complement the intake and exhaust on my Z. Everything seems to be working out ok EXCEPT that sometimes I get this LOUD vibration coming from under the vehicle. I don't think it's what you guys describe as rasp as it only does it sometimes and under certain situations. I hear it (I believe) after I lift my foot from the throttle and the rpm's start to slowly come down. I don't think it's a rattle between 2 pieces of metal as everything seems to be hooked up pretty tightly down there. It seems to be coming from within the pipes themselves. I can't really be sure since it's only done it a few times once i've been driving for a while. It's almost like a loud groaning sound that sounds different from what I consider 'normal'. Can you guys try and explain what that might be? I don't know if I should take it to the dealer to check out cause it might be normal. I believe I read a thread once about some of the gases running back up the pipes and causing this loud buzz. Any input would be greatly appreciated. Thanks!

 

I agree. To be honest, the *only* reason I keep contemplating keeping the Nismo is because the muffler and tips are so, so great looking. The tips are so perfect. The polish, the slight upward angle, the size (not too small, not too big), the rolled edges. Everything about the look of the Nismo is fantastic. But that's the only reason I'd keep it. Sound? Sure, it's great at full throttle, but I'm just too much of a weenie when it comes to *any* drone on the freeway.

Now, if I could just find someone to mount some Nismo tips on the stock muffler...

 

a good welder should be able to do it no problem.

 

Normal with high flow cats. My Fujitsubo exhaust made the same "tincan" noise when I had my cats on. The weld on my kinetix cats snapped in half this weekend and I had to put my stock cats back on (kinetix is replacing them, btw). The tincan vibration disappeared. Other cars that I have heard with headers/cats have had the same sound to a varying degree. Hope that helps.

 

Thanks for writing back. I hadn't received an answer so I posted a whole new thread to see if it would gain more attention. Well, what you're telling me does put me at ease a bit. I knew I would get different sounds from the set up and I guess i'm just not used to it. Like I said this particular sound is different from what the new set up sounds like overall but I guess it is normal. I just wanted to be sure in case I had to take it back to the dealer to get it checked out. Thanks for the reply!

 

My cats did that and after taking the car back to AAM I found out they were hitting the tranny. mine would make that sound if I put it in gear and held the brake. or even in revirse. Had AAM make some costom test pips and sound is gone. Just have some rasp to deal with but I am also changing out my nismo y-pipe for a AAm one with extra resonators in it

 

I had mine checked for it contact multiple times. It wasn't even coming from the cat area, but was resonation from the pipe on the exhaust itself. It isn't a rattling sound like something is hitting, it sounds more like there's a loose nut inside your exhaust pipe and it's rattling around.

Anyway, don't mean to hijack the thread...

 

But now where would I get a set of spare Nismo tips from?