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Exhaust drone AGAIN!

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Old Mar 13, 2018, 11:16 AM
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Exhaust drone AGAIN!

Drone seems like a common complaint about the EVO X. Before you get all, "it sounds great" or "you bought the wrong car", this car is so much louder INSIDE the car than I had expected. I owned a Galant VR4 for many, many years and I started the site www.galantvr4.org So, I'm a long time DSM/GVR4 guy. Drone is the increase in loudness inside the car that seems unrelated to the engine load and is dependent on RPM. It is the pressure inside the car that sounds terrible.

For reference, my GVR4 had a 3" turbo back Buschur Racing exhaust with a test pipe. It didn't have a resonator, had a test pipe, and had a small Dynamax muffler that Dave liked to use back then. It sounded great! No drone. The 6 bolt 4G63 sounded great!

Now, the EVO X... I've tried just about everything to make this car quieter INSIDE but just managed to make it quieter on the OUTSIDE.

Sound proofing: https://goo.gl/photos/KHTCueFDPKxkDAHTA
I also used some b-quiet on the roof and in the trunk.

- 3" MXP short downpipe
- 3" Ultimate Racing HFC with Mini-Muffler
- 3" Greddy RS exhaust that is modified. I removed the fart can and installed a Magnaflow 12589 muffler that is a single exit on the passenger side. This is the same muffler RRE uses in the "Super Stealth" exhaust. I still have the Greddy resonator. Pictures: https://photos.app.goo.gl/tjyBNIcBUQMhBwo62

I took at 4 hour trip in the car recently and it was terrible. I installed a free sound decibel meter app on my phone (yeah, not great accuracy) but it does show the drone.

Idle: 67 db
3800 rpm in 1st or 2nd gear on a smooth road: 77 db
4500 rpm in 2nd gear on a smooth road: 72 db
WOT in 3rd gear: max of 72 db
40 mph in 4th of 5th: 71 db. It bounces around a lot because road noise seemed to be the biggest noise maker and not the engine

When the car is cold, it is still just as loud at 3800 rpm. I also tried my economy map and I couldn't tell any difference in the exhaust sound.

So WOT is noticeably quieter than cruising at 75 MPH and the sound meter shows this.

I've got to find a solution to this or else I'm going to sell the car. I don't care if the exhaust is single or dual exits at this point either. It can be louder on the outside or at WOT but I want it much quieter at 75-80 MPH on the interstate.

So I'm thinking about these options:
- Replace the Greddy resonator with the same one RRE uses in their Super Stealth exhaust.
- Install a branch resonator.
- Buy a different cat-back. The ARK N-II has a Helmholtz resonator which they claim will stop the drone but it has a fairly small muffler and is pretty expensive just for a branch resonator.
- Return the catback to stock. I've read that people have liked a downpipe+HFC+stock exhaust but I am worried that will just be louder and still drone.
- I've even debated taking the dash out to put sound deadening material on the firewall.
- Return the entire car back to stock and sell it.

HELP!
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Old Mar 13, 2018, 11:37 AM
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Originally Posted by Jon Roberts View Post
Helmholtz resonator
I want to say, judging by your efforts this might be the best next step. Might eliminate it completely. The stock catback should also quiet it down a lot. But a properly calculated Helmholtz resonator should be perfect.

You might have seen this but:
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Old Mar 13, 2018, 01:48 PM
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Jon, buy an HKS Super Turbo... do it. You know you want to... wait, that was me.

As for a custom Helmholtz, it's easier said (youtubed?) than done. That style resonator is very good at eliminating a narrow frequency band but doesn't just magically work when you put a side tube on your exhaust. It took 6 iterations on my URS4 to get my car sorted out, but I really wanted to keep the mean 5cyl warble so it was worth it to me but it's tricky and time consuming. If you look into it, you'll need to somewhat accurately measure the frequency you want to eliminate and do a lot of math (there are some calculators out there) to get the right length tube/resonator/expansion chamber. And, for the record, the mic in an iPhone 6s does not cut it as a measurement device. It sounds like the ARK guys have done it already for you, for their exhaust, so that might be the right choice. Most of the guys on here like their Evo X exhausts obnoxiously loud so don't expect a lot of sympathetic replies.
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Old Mar 13, 2018, 03:05 PM
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If anyone else has done this, please let me know. I think the most logical solution is to hack up my current exhaust to see if I can fix it. If it doesn't, then I'll try something else.

wavelength = speed of sound / (Drone RPM * 2 sparks per revolution) / 60 seconds
1/4 wavelength = wavelength / 4

Drone starts at 3650 RPM which means it is 28.8" long.
Drone stops around 4000 RPM which is 26.35" long.

If I bump up the exhaust temp to 150 degrees, the lengths change to 29.95" and 27.34" for the drone range. I guess I'll go with 28" and see what happens.
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Old Mar 13, 2018, 05:47 PM
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I settled on the T1R Sparrow cat back exhaust and ETS resonated test pipe and I'm really happy with it. The drone is only a little louder then stock - honestly.
I searched for a drone free exhaust for ages and decided to go with this one and I'm pleased with the results. I have a small kid and too old for a loud exhaust and this one ticks all the boxes. It seems you have you tried a lot of options too so i dont want to shove an other exhaust at you, I know its frustrating having to buy with out actually hearing it in real life.
Also,
I tried a boost activated test pipe for a while and I just didn't like the sound it made under boost either.
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Old Mar 13, 2018, 06:45 PM
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Originally Posted by gazzer View Post
I settled on the T1R Sparrow cat back exhaust and ETS resonated test pipe and I'm really happy with it.
I thought the Sparrow was no longer available.
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Old Mar 14, 2018, 10:37 AM
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Originally Posted by Jon Roberts View Post
I thought the Sparrow was no longer available.
It's available, I only see it on evasive motor sports atm. I bought from them last year.
http://www.evasivemotorsports.com/mm5/merchant.mvc?Screen=PROD&Product_Code=T1R-18000-CZA-SES
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Old Mar 14, 2018, 01:20 PM
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I'm tempted to try the ARK N-II exhaust because it is supposed to be drone free. Before I pull the trigger, are there any other recommendations for drone free exhaust?
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Old Mar 14, 2018, 07:19 PM
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Originally Posted by gazzer View Post
I settled on the T1R Sparrow cat back exhaust and ETS resonated test pipe and I'm really happy with it. The drone is only a little louder then stock - honestly.
I searched for a drone free exhaust for ages and decided to go with this one and I'm pleased with the results. I have a small kid and too old for a loud exhaust and this one ticks all the boxes. It seems you have you tried a lot of options too so i dont want to shove an other exhaust at you, I know its frustrating having to buy with out actually hearing it in real life.
Also,
I tried a boost activated test pipe for a while and I just didn't like the sound it made under boost either.
What RPM does the Sparrow drone? I basically want to eliminate drone when in 5th gear on the interstate going 75-80 MPH.

I think the OEM exhaust droned too so a little more than stock doesn't sound encouraging but I've heard lots of good things about that exhaust.
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Old Mar 15, 2018, 12:53 PM
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Gazzer, thanks for reply and advice. I watched several in-car videos and everyone says it is quiet inside the car. Unfortunately, the only place I can find that sells this exhaust is Evasive and they just told me it is a 2 month backorder.
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Old Mar 15, 2018, 01:20 PM
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I say you give the resonator a shot. It's inexpensive and could be just what you need, especially since you're only looking to cancel a specific RPM range. I think the highway cruising gear/engine speed really makes these cars poor commuters. Lucky for me my commute is all 55mph back roads
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Old Mar 16, 2018, 05:28 AM
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Originally Posted by Jon Roberts View Post
Gazzer, thanks for reply and advice. I watched several in-car videos and everyone says it is quiet inside the car. Unfortunately, the only place I can find that sells this exhaust is Evasive and they just told me it is a 2 month backorder.
Good luck with what ever you decide to do Jon, I find exhaust and wheels are so subjective it's tough finding your perfect match. Let us know what works out for you!
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Old Mar 16, 2018, 08:48 AM
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Is that all you did as far as sound deadening?

You can't leave so many gaps in the material. You have to cover all of it, including the cross member/rails. And you have to glue together all the pieces using a vinyl cement. Any gap will let sound through.

You also have to get that stuff up as high as possible behind the console. I actually stuck 2 layers in the foot wells, but making sure not to affect the gas pedal. Most of the drone for me comes from the engine, not exhaust. When you hit 3800-4000RPM (right around 80mph) the car reaches industrial machinery levels. Everything else is road noise. Some of it is large metal panels (doors, roof) resonating at speed. For those, you want dynamat-type stick on material.

Here are some quick posts about what I did:

http://www.evoxforums.com/forums/sho...ostcount=27569

http://www.evoxforums.com/forums/sho...ostcount=27582

I definitely heard a difference immediately after finishing. Any noise was coming from the sides, the doors, and the lower gap there. I can drive NYC to DC with no issue now. Before that, the day after a 250 mile drive, I'd have a splitting headache and hate the car. And I still need to put the sound deadening material in the doors, and behind the rear seat. I expect that to make the car quieter Then I might try something for the wheel wells outside, possibly something in front of the firewall, and a lightweight material above the headliner.
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Old Mar 16, 2018, 05:47 PM
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I cannot stand a loud exhaust. No fart pipes here. I installed the magnaflow dual catback. Upgraded the flange to a full 3" (where it bolts to the cat outlet), but in the magnaflow midsection after the cat I installed a 3" vibrant resonator. This made what is considered a quiet exhaust, even better. I have a kid and one on the way and I would like them to keep their hearing. I can measure the length from the cat if you like, but honestly I did what fit and just ran with it. It seems good to me. With a testpipe I have made 420+hp to the wheels (220hp baseline) so it isn't limiting my car either. You don't HAVE to be blasting noisy and droning to make power.
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Old Mar 16, 2018, 05:50 PM
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Also I should mention that with past cars, welded (tube-style) exhaust manifolds or downpipes will BLAST and DRONE... Stay with CAST and THICK for the exhaust manifold and downpipe. I use MAP cast stainless exhaust manifold and AMS cast stainless widemouth downpipe. I think those also help to keep the sound at bay.
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