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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 09-17-2019, 08:29 PM   #15
Clutch Dog
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The fix for harmonic dissonance is all based with acoustics.

I had this issue with my catless headers and a muffled track pipe for the tip. The volume and sound was decent but the "buzzing" in my head was atrocious.

The fix is a 1/4 wave or "j pipe" using the helmholtz effect to your advantage.
Without getting into the gritty you need to measure which frequencies are most prodominate at whatever rpm you feel and then punch in some math (lotta math..) and youll get what size of pipe, the wall thickness and the length of pipe to weld on the side of your main tube. and that would help.

You can booger it slightly by using a chambered muffler with a length of pipe. Off the top of my head something like a 4 inch pipe at 2.25 ID at standard 0.065 wall thickness would need a 6 inch/8 inch chambered muffler to quiet anything from around 2-4k rpm
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Old 09-17-2019, 08:33 PM   #16
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I used dynamat and foam ensolite everywhere in the trunk area and I still have plenty of drone with invidia q300 which is supposed to be quiet. It’s not. I have a resonator in the mid pipe, still drone. Even had a helmholz resonator, still drone. These cars are tinny and noisy, but fun.
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Old 09-18-2019, 12:21 AM   #17
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Originally Posted by Contender View Post



You don't put it on the exhaust you put it under the back seat and trunk area inside the car.
I know that but it specifically says for pipe use and it's in the name. Knowing some of the people on this forum, they might not read between the lines or the fine print.
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Old 09-18-2019, 01:09 AM   #18
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Many thanks to all, I was thinking that it was just resonance, I think I have to live with the noise. I'm probably just getting too old...
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Old 09-18-2019, 11:58 AM   #19
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It got so bad on my car I went back to the stock muffler.. and i cried a little on the inside..
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Old 09-18-2019, 12:24 PM   #20
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Many thanks to all, I was thinking that it was just resonance, I think I have to live with the noise. I'm probably just getting too old...
You will get used to it. Then when you drive something else it will sound weird.
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Old 09-18-2019, 12:46 PM   #21
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Just turn the music up.
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Old 09-18-2019, 12:48 PM   #22
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Many thanks to all, I was thinking that it was just resonance, I think I have to live with the noise. I'm probably just getting too old...
Then, when you get a bit older, you won't hear it anymore -


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Old 09-18-2019, 01:56 PM   #23
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No, sound insulation won't do much. Your resonance comes from the exhaust, not the trunk.
That's not entirely accurate. Yes, the exhaust will resonate at whatever frequency it decides to (based on your specific configuration), but the interior of your car also can act as a resonating chamber (no differently than, say, a subwoofer enclosure) and when your exhaust hits the resonating frequency of the body, you can get some pretty awful drone.

Case in point: My car. I have a very unique exhaust combo on my car at the moment, and there are VERY big differences in the volume inside the cabin depending on the interior configuration. With the rear seats in their normal configuration, the cabin is relatively quiet. If I fold the rear seats down, I get some pretty significant drone around the 3-3200 RPM range. However, if I open the windows, most of that drone again goes away. None of that has to do with the exhaust configuration. It has to do with the "enclosure" in which those sound waves are bouncing around.

I have a thick slab of Luxury Liner Pro (like 1/2" thick, closed cell foam) that I slid behind the rear seatback felt. Not sure how much that contributes to the relative silence with the seatbacks up (as compared with the seatbacks up but WITHOUT that foam) but the point there is a lot more to interior resonance than JUST the exhaust setup. Obviously, a quiet, non-droney exhaust setup will prevent the issue in the first place, but if you do have a droney exhaust, your interior setup can be the difference between a quiet ride, or a miserable one.
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Old 09-18-2019, 06:46 PM   #24
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deadening. there's another fucking e in the word!

No, sound insulation won't do much. Your resonance comes from the exhaust, not the trunk.


Excuse me while I bish slap you for being a dusty hoe , leave the mate alone for fucks sake !


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Old 09-18-2019, 07:29 PM   #25
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............….your interior setup can be the difference between a quiet ride, or a miserable one.
Yep, I found that the exhaust sound when the trunk is empty is one level of sound in the cabin, but, when we travel and the trunk is full, the interior of the car is significantly quieter.

And, that is a good thing; so I can clearly hear mrs humfrz's comments on my driving:

* I didn't mean to scream, but I didn't know if you saw that car coming.

* why didn't you park there?

* why do you always park so far away?

* why do you always park so my side is next to a curb?

Just to name a few -

(then she wonders why I don't take her out more often)


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Old 09-18-2019, 08:12 PM   #26
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God damn. The drone of whining in this thread (not OP) is stunning.
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Old 09-18-2019, 08:49 PM   #27
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This helped with my tomei 80. 16 inch vibrant.
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Old 09-19-2019, 07:02 AM   #28
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Yep, I found that the exhaust sound when the trunk is empty is one level of sound in the cabin, but, when we travel and the trunk is full, the interior of the car is significantly quieter.
Exactly. I've noticed if I have the trunk loaded a certain way, I can get interesting beat frequencies from my exhaust sound, lol.
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