Exhaust Resonance

[Import Convert]

Ok guys I'll try and make this as short as I can. Last year I purchased an exhaust for my S14. It was a generic 3" N1 cat back off e-bay. Yeah I know mistake number one. I really liked the look of it though and fitment was actually pretty good.


Drove around a few months like that and grew tired of how loud it was (no silencer). In the pic I have the silencer installed but, I took it out. It made the car sound like it was farting. Plus a silencer defeats the purpose of a 3" exhaust. So instead of buying a new exhaust one I sought to modify what I had. I purchased a 3" magnaflow muffler perferated steel mesh core to replace the resonator that was on the N1. I also painted it VHT black.

It helped a TON. Gave the exhaust a nice deep tone. With that being said driving around town was much more enjoyable. No more worrying about cops or attracting too much attention.

Since then I have had this odd resonance at highway speeds.
About 70mph or when the RPM's are about 2,750. I'm now looking for ways to eliminate this resonance. It's definetly coming from the exhaust. Mainly the N1 can itself. I'm looking at all options here dynamat, new exhaust or add a flex pipe to the exhaust somewhere to reduce pipe resonance. The car is a automatic 95 S14 with a 3" cone filter on stock intake piping,stock manifold,downpipe and the dummy cat. Looking for some input or solutions. Bounce ideas back and forth just let me know if any more info is needed from me. Thanks for reading.

[S14DB]

Still using the stock hangers?

[justinedible4]

My previous exhaust had resonance as well. It was an ebay cat back and I had the resonator replaced with a dynomax ultra flo welded and the exhaust would resonant at several diff rpm levels, such as 2700rpms. I have since then replaced the dynomax with a borla and have had no problems.

[Import Convert]

Originally Posted by S14DB

Still using the stock hangers?

As in the ones on the chassis itself? Then yes. New hanger bushings as well.

[Import Convert]

Originally Posted by justinedible4

My previous exhaust had resonance as well. It was an ebay cat back and I had the resonator replaced with a dynomax ultra flo welded and the exhaust would resonant at several diff rpm levels, such as 2700rpms. I have since then replaced the dynomax with a borla and have had no problems.

Well see whenever I put my head down near the exhaust where the magnaflow is it's just a deep mellow tone. Now when I do the same thing at the end its the same tone just much,MUCH louder. That's why I think the N1 is the issue. Im not entirely sure though.

[S14DB]

Remove the muffler heat shield above the N1. I noticed that mine started acting like a passive reverb putting resonance into the trunk. Put the bolts back in to seal the trunk once you remove it.

[Import Convert]

Originally Posted by S14DB

Remove the muffler heat shield above the N1. I noticed that mine started acting like a passive reverb putting resonance into the trunk. Put the bolts back in to seal the trunk once you remove it.

Alright I just went outside and removed it. I drive about 10-12 miles on the highway to and from work each day so I'll give it a shot and post back here tomorrow after I get off work.

[JKL1031]

try speding up a lil to 3k if u can. my car is alot more quiet at 3k that crusing at 2.5 or so.

[Import Convert]

Originally Posted by S14DB

Remove the muffler heat shield above the N1. I noticed that mine started acting like a passive reverb putting resonance into the trunk. Put the bolts back in to seal the trunk once you remove it.

Okay so here is the update on the removal of the heat shield. I did in fact notice a difference. The differenece was minute but, what's important is that I noticed it. I feel that I have VERY good hearing although I may have just been experiencing a placebo effect(my ears telling my brain what i want to hear). Either way it has inspired me to further investigate way of sound deadening. I purchased 4SQ.FT. of Dynomat and picked up a can of underbody coating.

With all that at hand I figure that I can use the dynomat to cover the area inside the trunk directly above the muffler and the parcel shelf/rear speaker deck to eliminate noise being transfered into the cabin. I will then coat the area where the stock heat shield once was with at least two coats of the underbody coating. It's going to rain today so, install of everything will have to wait till tomorrow. Unless I get impatient. I'll post photos of where exactly i place the dynomat if possible.

[arkive43]

hrmmm could be the 3in diameter piping its self, i notice on n/a engines it tends to "rattle" more due to the lack of back pressure?

[S14DB]

Originally Posted by arkive43

hrmmm could be the 3in diameter piping its self, i notice on n/a engines it tends to "rattle" more due to the lack of back pressure?

No

[fliprayzin240sx]

You sure the exhaust isnt touching the subframe. My car had one of these generic Ebay shit and the flange was vibrating against the subframe. Took it out and slapped my Apexi GT Spec and reminded me how I like quieter exhaust better.

[Import Convert]

Originally Posted by fliprayzin240sx

You sure the exhaust isnt touching the subframe. My car had one of these generic Ebay shit and the flange was vibrating against the subframe. Took it out and slapped my Apexi GT Spec and reminded me how I like quieter exhaust better.

Yeah im pretty sure it's not touching anywhere. I can run my fingers all the way around the exhaust from the dummy cat to the tip. It does get REALLY close at one point just after the first bend. Its possible that it could be transfering some vibration via sound waves at that particular spot. Im just speculating though.



Update on the dampening solutions. I was able today to install the dynamat and coat the underbody where the stock heat shield was.


Now I haven't had the time to highway drive with things like this but, at idle and just crusing the streets. It's definetly more quiet. At idle you barely notice the exhaust and city speeds produce only a very deep sound. This is what I percieve from inside the cabin. I'll be sure to report back on Highway results to see if that ominous hum is finally gone.

[Import Convert]

Update on Highway driving:

Okay so here is the update I said I would give everyone. First thing I notice is the overall loudness inside the car. Putting the dynamat im sure made a difference. The ominous hum is still there but, I'd say 20db or so quieter. Considering that all I invested was about 40$ in supplies and a little time. It was definetly worth it. Hope this helps out others.


Side note: If I could go back and shop for a new exhaust i would go with a 2.5". If your N/A it's simply not worth the extra sound levels of a 3" exhaust. I'm not disputing the advantages of a 3". Just giving a real world experience and opinion.