Finding the right catback is exhausting!
 

It really is... Help me pick out my next exhaust attempt? I haven't paid enough attention to exhausts to have a good in-person baseline in memory to compare opinions and videos to. Hoping we still have some exhaust fanatics here who can help a noob.

Short version of the story is the HKS Hi Power Spec L I put on this spring sounds great but drones like a MF between 2.5 and 4k. Massive spike in the 110-120Hz range. JDL4-2-1 EL -> JDL OP -> JDL UQFP. Tried the stock FP with basically no change in drone.

I like the sound of the HKS. I just can't handle the drone. I need something that has at most 10% of the drone. I COULD go back to stock. But I really don't want to lol.

Priorities beyond sounding good/hks-like?
1. Needs to pass sound at Ax events
2. Needs to have no to very, very little drone
3. Budget is... I'd like to keep is around or under 1k if possible.
4. No heavier than stock, lighter is better
5. I think single exits look interesting in a good way, but it's not that important.

Some I've looked at recently:
-Tanabe Concept G: Seems perfect from what I've heard, except it's too loud
-Invidia q300: Seems a bit too mild
-Fujitsubo AR: Seems just a bit too... Sharp? ...for my taste. Idk sound is hard for me to describe.
-Apexi N1: Seems mild, but less so than the q300 from what I can tell. Edit: oh there's different versions of this one... The more I hear it the more it kind of grows on me...

What should I be looking at?

I’d talk to a local exhaust shop about adding another resonator to the mid pipe.

I did think about that, but I am not even sure where they could put it except somewhere after where it splits? Maybe some kind of j-pipe next to each can?

The way I'm looking at it is that for about the same price as customizing the exhaust I can probably sell this and get something else. Risk of changing the HKS so that it's worth less to someone with a stock header it vs risk of a new exhaust not being what I wanted is tricky lol.

You need to find something with a suitcase style muffler.

Also, buy just a little panel vibration damping for the trunk pan, it helps a bit. I just did mine and was surprised by the change in buzz. I'd say almost nothing else will amount of a notable change, short of a properly engineered helmholtz resonator setup.

You just had to say this part didn't you... This is too tempting and I'm gonna spend way too much time on this now.

Hahahaha I'd say maybe we'll worth the endeavor!!!

It totally isn't lol.

Hypothesis 1: Header is increasing average temperature of the exhaust flow, moving a resonant to that of the cabin.

Hypothesis 2: Header increases the temperature of the exhaust past the hemholtz resonator, kicking the relatively cooler resonator out the impedance band needed to counter the drone. In some cases making it worse.

Hypothesis 3: Header is inducing a frequency not present in the stock one due to new runner lengths.

I think some combination of 1 and 3 is the answer, and at that point I (ok, someone with welding skills) can probably either alter the length of the existing resonator or add another one or two. In order to prove/calculate that...

Need: IR thermometer, high temp thermocouple, calibrated microphone, software? Possibly someone else with an IR thermometer and stock header...

I need to take a temperature profile of the whole exhaust exterior (after it's nice and hot), then adjust for the thermal conductivity of the walls. Adjust based on actual outlet temperature measurement. Use that to calculate speed of sound at a bunch of points in the exhaust and find a best fit equation for different sections. Then I need to measure/look up the lengths and IDs of all the exhaust sections. Next do some calculus (speed of sound is variable) to find the resonant frequencies of every combination of pipe section since every change in impedance reflects a portion of the wave. Use the microphone to take a sound profile at different points under the car and in the cabin to find the drone frequencies. Compare calculated resonant frequencies to measured frequency to find what is causing it.

Grab the temperature of the piping on the stock car between the cats and after the second cat to adjust frequency calcs. See if calcs show hyp1 or 2 to be correct. Maybe get a sound profile here as well.

Use that information to design adjustments to my exhaust. Implement and hope. Test. Profit. (or cry and try again...)

This is all your fault.

If you have not seen these already:

This YT channel has a sample of each JDM exhaust sounds, including the common and not-so-common ones.

https://youtube.com/@xacar86brzmagazine63

https://youtu.be/QV_ndoTr08E

When I first read this, I thought you were talking about a product that was specifically made for our cars for this purpose.

But after rereading it, I think you are talking about just using a section of dynamat/lizard skin for the bottom of the trunk?

Yeah sorry, I just hate calling it "Sound deadening" so I tried to be fancy. I was so surprised by how thin the metal was over the exhaust!

I like to be fancy sometimes too lol! :cheers:

I think that between the sound deadening and those JDM hangers a good bit of exhaust noise/drone could be mitigated.

I have heard a couple people now say that the hangers can help. I switched my hangers out to pretty strong ones and didn't notice any difference, just that the heavier exhaust wasn't droopy. I wonder if there's something special about the STI hangers aside the durometer

I've got the hangers. It definitely helps, but the drone is still pretty bad.

The JDM hangers have both a different shape and compound. Theoretically they are better at damping certain frequencies that resonate in the cabin.