Over the last few months I've been doing some testing with my stock and Nismo exhausts. I wanted to see just how much exhaust loudness gets affected by adding high flow cats vs using stock cats. I spent the time doing a lot of exhaust swaps purely because of the huge disparity between what different folks were saying about their exhaust loudness. I heard folks saying the Nismo, for example, was only a little louder than stock, and wasn't bad on the freeway. Then, someone else would come along and say just the opposite. With a little digging, I found that the people complaining about the Nismo being too loud happened to have high flow cats or test pipes.

So, I did a bunch of comparing on my own car by swapping parts back and forth. Here are the combinations I did, in the order I tried them in.

Stock exhaust, stock cats:
We all know what this sounds like. This will be the reference loudness level I'll use as the basis for my comparison. Relatively quiet around town, no droning on the freeway, only really gets loud at full throttle and high rpms. Unfortunately, I didn't do any sound level measurements with a sound meter with this setup.

Stock exhaust, Kinetix cats:
This was a bit louder than stock, but still not intrusive at all. Had the same tone as stock, but had a small bit of raspiness at some rpms under full throttle. Did not drone on the freeway at all. Still a very quiet exhaust.
Loudness registered about 70-74 dB (A-weighted) cruising at 75 mph on a flat freeway, depending on the pavement type.

Nismo exhaust, Kinetix cats:
Sounded incredible, but was much louder than my previous setups. Deeper, louder rumble at start up and driving around town. Much, much louder sound at full throttle and high rpms. It was all fantastic except for the freeway droning; this was quite bad. It was loud enough that our ears would start to hurt after a few hours on the freeway. When going up slight inclines the drone would get so bad my girlfriend and I would have to raise our voices significantly to hear each other. Cell phones were useless. On long road trips the droning would grate on my nerves so bad and start to become so uncomfortable that I'd have to wear ear plugs.
Loudness measure 74-78 dB on flat freeways (depending on pavement type) at 75 mph, and would hit 80+ dB going up hills. I think the real problem here (that the dB meter won't show you) was the frequency of the drone. It was at just the right frequency that it really dug into your skull.

Nismo exhaust, stock cats:
This is what I have now. Much quieter! It still has the same tone and "feel" that it had with the Kinetix cats, but much quieter. Still has a deep, angry tone at start up and when driving around, and is still pretty loud when at full throttle. However, freeway drone is almost gone. It's still there a little, but acceptable. It can still get a bit tiresome when going up long inclines on the freeway, but at least it goes away once you are going flat again.
Sound level measurements are the same as stock exhaust with Kinetix cats, with a 2 dB increase when going up mild hills. Once again, it's not necessarily the loudness that gets you on the freeway, it's the frequency of the tone. I'm going to try and stick with this combo for a while, just because it sounds so nice around town and, in my opinion, is the best looking Z exhaust available. The tips are just fantastic.


And that's it. I have not done any dynos to measure power differences. To be honest, the 3 latter combinations all felt about the same in terms of power. That is: a bit more than stock but not a ton. Of course, my butt dyno might not be as accurately calibrated as some folks around here who believe they can feel a 2-4 hp difference.

 

Interesting. This has me not wanting to get cats or test pipes. I can't stand highway drone. That would just drive me insane.

 

The stock exhaust, with high flow cats, has no drone. Still a very nice, quiet exhaust on the freeway. Aftermarket exhausts seem to suffer the most.

 

I have heard the Nismo and Fuji exhausts the be the quietest of the aftermarket. I have also been told that Fuji manufactures the Nismo?? Anyway, I was in the market for high flow cats (helix, kinetix and crawford). But after reading your post I am thinking twice about going down this route. However I wonder how comparable the sound of the Helix is with the kinetix?? I have already ordered a Pro-1 Y pipe and wanted Helix hi flow cats next and a fuji legalis exhaust last and now i am wondering how annoying and loud this setup will be.....any ideas??

 

Aftermarket y-pipes shouldn't make any sound difference compared to the stock y-pipe. I noticed no sound difference at all when I put on the Kinetix y-pipe. Didn't expect to, really.

As far as getting high flow cats, you might give it a shot and see what you think about the sound with the stock exhaust. You might like it how it sounds and won't have to spend money on the Fuji. If you do cats and a y-pipe, that should cover the real flow problems. The stock mid-pipe and muffler are actually pretty high flowing from everything I've read. Replacing them would be for sound only.

 

Isnt the fujitsubo quieter then the Nismo? Wounder how this and cats would sound.

 

Yeah, a friend of mine has a Fuji, and it's pretty quiet. With stock cats on both, I'd say the Fuji is a bit quieter. Not sure how much louder it got when he put his Kinetix cats on. I could ask him if it was significant. Certain exhausts seem to be more affected than others. The Nismo gets a big increase in volume, but the stock exhaust only gets a small increase.

Another friend of mine has a G35 with a Borla and high flow cats, and it's still extremely quiet inside the car. Much, much quieter than my Nismo with high flow cats. You can barely tell he has anything other than stock unless you are full throttle at high rpms. However, the G35 has a trunk instead of a hatchback, and that tends to reduce exhaust loudness tremendously inside the car.

 

nice thread; thanx

 

Yeah, I am debating weather to go with Nismo or Fujitsubo. I might want to get crawford cats, so I am really stuck on which exhuast to get.

 

my first mods. was the resonated kinetix and nismo exhaust, before i have 'em , i heard that the nismo is a bit louder , and i've get shocked when i installed the whole system , MAN THAT THING IS LOUD , i've even doupt that in any time i'll be stoped by police,

my problem is that i installed them together (exhaust and test pipes) , but after i read this thread now i know what to do , tomorrow morning i'm going to remove my pipes and use the stock cats.

if i do get quieter sound , then jreiter<=== i owen you one

i'll keep you updated

 

Yeah, it'll get way quieter with stock cats. No doubt.

 

today i've removed my test pipes and but my stock cats.
i've been driving my car (with nismo exhaust and test pipes) for about 2~3 months. and when i removed the test pipes i kept thinking if i do have an exhaust that quiter than the stock one???
thats because i used on the loud sound of the last setting.
what i can tell is the nismo exhaust is not just quieter with the stock cats. but it QUIETER and believe me it have a really really nice sound and almost a perfect level of loudness ,
and if i knew it that the test pipes will make that difference in sound , i'll say i shouldn't pay 1 $ for 'em (i paid 320$+ )

inside the car you can't even notice that you have the exhaust (while cruising ) ,and when steping on it , just listen to the sound..... really i can't discribe what it look like but now i'm really happy with my setting

and jreiter you are the man, and i do own you one

 

I'm glad you like it! I reacted the same way when I switched back to stock cats. What I would like to see are some high flow cats or test pipes with *two* resonators instead of one. I imagine that would quiet down the loudness and be similar to the stock cats.

 

Can anyone with headers and stock cats with an aftermarket exhaust, post their reviews of thier sound levels?...

 

"Sunshine" is in the shop getting Nismo Cams and Headers. Already have Nismo CAI and CatBack installed but left the stock Cats on. I'll report when she's set free, and try to attach a .wav file.
Any other suggestions welcome.

JT

 

I'm very interested to see what this sounds like. I have the Nismo Exhaust and CAI and am thinking about getting the Headers. Can't wait for that .wav file!

p.s. Thanks jreiter for a great thread.

 

I just put on headers and HF cats and kept the stock catback. I couldn't believe the volume bump...not obnoxious, but much louder at WOT - especially in the 3-4k rpm range where it sounds mean as hell - I'd describe it almost as a high pitched motorcycle wail - definitely not what I'd call raspy. b.t.w. how would you describe raspy?

Part-mid throttle has a more throaty agressive sound which is v. nice!

Free-reving gives some nice pops and gurgles too.

 

Nice comparison
I've been debating over getting high-flow cats or Nismo exhaust.
This helps a lot.

Thanks for sharing