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Discussion Starter · #161 ·
K, well, lacking any sort of definitive direction I'm going a few ways...

Since I've already run this by Magnaflow, Borla, Dynomax, and Flowmaster without any helpful response whatsoever, the I'm gonna pursue the following paths:

1) I sent a feeler to MBRP explaining my issue and asking if they had any attenuation data on their R1017, and also if they had any ideas on anything that might help. Their stuff generally seems technically along the same lines as any other US aftermarket exhaust manufacturer, and I know many of their systems have drone complaints, but hey what's the harm?
2) I sent a feeler to Corsa explaining my issue and asking if they had any devices that suit this scenario. They make extensive use of frequency cancellation, in their RSC branding, to deal with this sort of thing. Their off the shelf options in the muffler only space are targeted for V8s, but they're semi local to me and it seems like they do offer custom solutions.
3) I asked my exhaust shop if they have any recommendations. They do lots of custom work like this, and promised me some feedback after doing some investigation.
4) Find a Helmholtz resonator that handles this frequency range and fit it somehow. This seems like kind of a hat track option, and initial research seems to suggest that it would take multiple attempts and welding...so I most likely can't do it myself.
5) I can add the Thrush 24241 or MBRP R1017 and hope for the best. This is pretty low risk. A glasspack-like setup like this will only make things quieter and add weight and there's a remote, but present, chance that long ones like this might have a better chance of capturing lower frequencies.
6) I can swap the DBX out for a Vibrant Streetpower (or something else?). With the revised pipe routing I've got now, and bumper cut to accomodate a center/center muffler, my tape measure suggests a Streetpower should fit. It'll have to sit a bit futher back, to clear the sway bar mount, which it has to do for the tip to be far enough out anyways. I've heard the black model on a couple other swapped hatches, and they are not quiet, but I sure as heck don't recall ear crushing drone.

Any one or combo of these things has a chance of ultimately working. None of them are particularly cheap, especially after labor (particularly if multiple trips are needed).

I guess my last resort, nothing promising pans out, route would be 5+6. I've already got a decent size muffler in there so, who knows, maybe it plus that could be enough.

--Matt
 

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Discussion Starter · #162 · (Edited)
After further reflection and discussion, my exhaust shop has done J-pipe setups and believe they can make something work. I'm otherwise really happy with how this sounds, so I guess we'll see how well a spot can be found to fit the required 44" of pipe to cancel that frequency.

--Matt
 

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2008 FG2, CAI, J35, PLM 4-2-1, anti reversion chamber, Envida, TSX cams, Hondata
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Thanks for the update.
So if I understand correctly, the previous setup is on the shelf and the new setup consists of the QTP AR3 followed by the Flowmaster DBX ?
And you noticed an overall reduction, but not much? Or yes noticeable?
I was curious also about which motor mounts (durometer) you went with and whether it is a contributing factor to interior NVH.
Wood Floor Gas Hardwood Machine


Motor vehicle Wood Automotive design Gas Bumper

This is the current J pipe idea I'm playing around with. On pipe slides over the other to create an adjustable length for tuning. Secured with heavy duty band clamps and can be welded after final length is determined.
 

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Discussion Starter · #164 ·
The previous setup is in the bin. 😂 Yes, though, QTP AR3 followed by Flowmaster DBX. The sound reduction, overall, is actually huge. It's massively quieter at most frequencies now. This configuration just didn't help my drone problem at all, which is why I'm going with the quarter wave setup.

Still measuring and shopping for parts. Will share what I've got lined up once I've got a better view.

I have the softest Hasport mounts, 62A durometer.

--Matt
 

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Discussion Starter · #166 · (Edited)
79Hz. There are also smaller spikes at multiples of it, which the 1/4 wave resonator should sort out. 79Hz on the dot is the issue, now, though.

I seem to have room in the same spot this guy did his:

Glad his worked out well, but I think his calculations based on exhaust gas temps were not spot on. All I've read suggests I should be aiming for the temp of the device, which should be closer to 110-120° F as far as I'm measuring/estimating.

--Matt
 

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Discussion Starter · #168 · (Edited)
I strapped it on again yesterday evening and, as with before, it didn't make any tangible difference. The noise is all coming out of the exhaust tip, and it doesn't seem like any structural dampening from the damper impacts the overall perceived or measured loudness. It's wild, though, that I can place my palm nearby the tip and it drops to stock-like loudness. I'm not done with hope on that, though. Who knows, maybe it'll be icing on the cake after the 1/4 wave deal is in. :whistle: I'll tell ya what, though, it sure is convenient to have that on that mount setup. Just takes a jack and a few minutes to pop it on.

Ok, measurements done and parts ordered.
1x Vibrant 13032
4x Vibrant 2694

The shorter leg of former minus ~1" should fit well onto the pipe entering the rear of the DBX, and can point up at a 45 degree angle to get the longer leg to a point where the latter can be looped to the desired length. Each U bend has 11.7" of tube, on the center line at least, so I should reach my required 43.8" of tube (assuming 120 degrees Fahrenheit). I'll make more precise measurements once I've got parts in-hand and can reason better on the actual proportions, but it should take ~3 of the U-bends assuming as much of the 90 degree pipe as I think will fit does actually fit.

Based on the upper/lower limits on frequency that I've captured, and the temperature ranges I'm reviewing, the pipe needs to be between 40" and 48" at the limits. My intention is to split that range and shoot for 44" and hope for the best. In the event that that doesn't go according to plan, I'll cut it and use but clamps like these to shorten/lengthen the tail end until I find the exact correct length and weld it again to that length.

My intent is to start with 3" on the shorter leg of the 90° pipe, and 5" after it. That adds up to 3+2.4+5"=10.4". 3 whole uncut U bends (4+4+7.5)*3= 46.5". Altogether that is 56.9", which is well over the target length to reject 79Hz at any reasonable temp. As far as I can tell the target freq +/- 3Hz (or even 5Hz) should be rejected with at least 50% efficiency so hopefully close enough to start once I lay hands on things and can dial in the exact numbers a bit more closely.

--Matt
 

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Discussion Starter · #169 ·
Looks like the leg into the muffler will actually be closer to 2.5", rather than 3", but here's a scale model:
Automotive design Toy Font Cylinder Logo

Azure Rectangle Finger Plastic bottle Font



This lands at exactly 44" of pipe and +/- 4" should be doable.

--Matt
 

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Discussion Starter · #170 ·
Oof, upon closer inspection the 1.5" CLR 90° bend is no bueno. Unlike the larger radius bends, these do kink down a bit. Apparently discontinuous bends like this cause sound wave distortion which undermines the intent of the device. 😞

Wood Wood stain Fixture Door Hardwood


I wanted the 2.375" CLR bend Vibrant 13046, but neither Jegs nor Summit had it available quickly. I found somewhere that can supposedly get it to me this week and ordered it.

Doesn't make a huge impact, overall, in the design. The cap section ends up being 1.25" instead.
Rectangle Font Material property Magenta Tool


Should have this built and installed Thursday. 🤞

--Matt
 

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2002 DC5 Type S
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Since I've already run this by Magnaflow, Borla, Dynomax, and Flowmaster without any helpful response whatsoever, the I'm gonna pursue the following paths:
This is a badass thread man. I think you are the 1st member to post exhaust component testing for decibel levels and custom system additions to reduce unwanted drone sound. Good job.
 

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Discussion Starter · #172 · (Edited)
I apparently forgot to share the final setup for the tuned mass damper. It came out pretty well.
Hand Tire Automotive tire Bicycle tire Road surface


Going tomorrow to have the quarter wave setup.🤞 I'm going to have them finish it with a clamp and a couple of possible end cap options so I can adjust through the temp and frequency range I'm targeting.

--Matt
 

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Discussion Starter · #173 · (Edited)
The quarter wave setup went in pretty well. I had them set it up initially for my 110Hz target.

Tire Wheel Vehicle Motor vehicle Automotive tire


The clamp leaks, which isn't ideal. It also doesn't prevent twisting, so I had to do some questionable ziptie stuff for my 80Hz configuration test, but it is good enough for testing.

In 110Hz trim at 50mph in 6th that range was definitely reduced.
Colorfulness Rectangle Slope Font Line


I swapped it to 80Hz and saw:
Colorfulness Rectangle Slope Font Parallel


Temps of the device seem to basically represent ambient +10°F, though, putting it at 60°F during that second test.

I don't normally drive the car while it is this cold out, and my calculations miss the target frequencies by 2" and 3" at each respective frequency because of the speed of sound differences at those temps, so I think I need to re-test in warmer weather.

Subjectively, the 110Hz setup (or, I guess, technically 105Hz at this temp) setup seemed slightly more pleasant to my ears. I can tell the 80Hz stuff is reduced with the bigger one, but I think the 110Hz noise bugs me more.

--Matt
 

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Discussion Starter · #174 ·
Weather seems to have finally broken, and I got better clamps (VW OE clamps from a Euro car with a factory 1.5" exhaust - real sturdy).

The best setup I've found so far is the 80Hz loop I had setup with an additional inch added to the final straight section. As long as the temp is over 65-60, it seems to keep my drone situation at bay once it's warmed up.

I'm not totally convinced that the mufflers haven't also broken in a bit and are doing their job better, and I've not yet had leisure time to do recordings and measurements since I've been busy preparing for a track day Friday (first one in this car).

I'll try to get something up sooner than later. I found a vac leak during my shake down because some past problem ate the IAVC gasket and was letting air in. Not totally sure what happened there, the gasket looked like this and there was a mountain of corrosion inside the side where the leak was. There's been no coolant going through there since this setup was built, so it must have come with the TB.
Gesture Wood Finger Flooring Line


I just put on a Karcepts delete plate and new gasket and she's running fine. I'm actually amazed how well the car starts and idles without that valve, and may leave it off permanently. Not sure yet. 🤷‍♂️ Apart from needing to goose the gas to 1.5k for 10-15 seconds on startup, it starts and idles fine even in wet 50 degree temps with the screw set such that my eventual hot idle is 850rpms. Low speed drivability and idle are massively improved compared to how it was leaking.

I wanted to swap my junk2 upper control arms to non-adjustable ones, since the car sits higher now and doesn't need em, but I can't for the life of me find anywhere that can get them to me quickly. Even summit is out of stock on every single option they sell.

--Matt
 

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Discussion Starter · #175 ·
Ok, it was sad to have the windows closed on such a nice day but I did it for science 😎

Here's 30mph in 4:
Colorfulness Light Rectangle Slope Font


40mph in 5:
Colorfulness Rectangle Slope Font Line


And 50mph in 6:
Colorfulness Rectangle Font Line Slope


I think I'm 99% on adding an additional tube-shapes resonator, but my ear piercing 80Hz problem is totally gone. I don't know where the new 152Hz sound came from, and I don't love it, but the car is overall loads more tolerable to drive around. At highway speeds, there's no hint of drone and it is quite tolerable.

--Matt
 

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Discussion Starter · #178 ·
Here's ~35mph:

And 50mph:

Haven't decided on whether I'll add the MBRP or the Thrush resonator. The MBRP is slightly larger, but their stuff does tend to be on the rowdier side while the larger Thrush glasspacks tend to be a bit more tame.

--Matt
 

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Arouse the DAMPFHAMMER!
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Thanks for sharing your investigation approach and results, which I really appreciate. I love that stuff you are collecting here!

Here's idle:
Wow, that is really loud compared to my DAMPFAHMMER setup. I had to decrease the gain of my headset to 30 % to feel comfortable.

I'm bad at video but I tried to make a clip of 70mph with a spectrum overlay and this is how it came out:
All what is need is in the video, perfect!

Rectangle Slope Plot Font Line


These lines are the pressure waves from 1 m distance and 45° spread on frequency and linear dB-levels. Black = [email protected] rpm, Green = [email protected] rpm, blue = [email protected] rpm and red is accordingly exhaust. On idle the noise level is equal to the one of my wifes 45 hp 3-cylinder NA engine, just a bit of load and it goes really different.


What you hear is more the engine valvetrain and EWP then the exhaust. Sounds more like a process facility as an race engine at idle speed. But still can do this...


Shift through first 4 gears up on a stock Y2M3 gearbox. It may doesn't look fast but this was from roughly from 35-180 km/h (22-112 mph) in around 6 s.
 

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Markus, sir, bro, I can tell how fast the Lotus is with the DAMPFHAMMER engine from a 2klm away or 1 mile"ish"...

Sounds sick. I need to get my sloth self off the shelve and complete this build so it runs and I can enjoy it and cruise to Canada
 
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