Fancy Tech: How to Get Rid of Exhaust Drone, works great!

Rusty

It's not about volume. It's the length that matters. You tune it by changing the length. The pulse wave hits the end of the capped tube and bounces back into the exhaust pipe. What you want, is that pulse wave to hit the other pulse wave coming down the exhaust at the right time to cancel out the drone. The problem is that you can only tune it for a narrow rpm range.

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solteroblues

so, Beemerkid, did you ever finish this? What were your results? I went to a couple of muffler shops, one refused to even try, one was willing but wasn't sure the Injen exhaust was really metal (haha) to weld properly... Going to two others for quotes, but still no success in getting the work done...

solteroblues

I got mine done today... I couldn't be happier. I had a local muffler shop weld in a pair of 26" long capped pipes upstream of my mufflers, and they go out on the back side and up over the cans... You can't see them at all from behind the car, and it basically eliminated all of the problem areas. I can drive through my neighborhood or at cruising speed and I have no droning at all between idle up to about 5k rpm. Up there it does come back some, but I'm rarely at that rpm for more than a few seconds, and I don't mind the loudness when I'm at WOT, it was just the cruising speeds that were killing me!

I did quieten down the entire system, but that's ok, it still has the deep rumble that I like, just not at neighbor waking volumes...

future370zzz

I'm selfish and want it a little louder on the outside and quiet on the inside.
Overall though, not having to deal with a headache after every long drive is nice.

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solteroblues

that's pretty much what I have now... whereas before, it was louder inside than out!

TBatt

Great to hear, or should I say not hear.....

Since adding in the supercharger and having Seb work his magic the 2-2.7K rpm range has gotten really loud when under load. When my wife is with me I stay out of that range by staying in a lower gear. I might have to give this a try as it does get quite loud while cruising below 80.

Thanks for letting us know that this works. ROLL RIDE!!!!!

BTW: Did the shop use 304 stainless?

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RJM pedal, Hotchkis Sway Bars, FI TDX, FOG Light, Z1 Slotted Drilled rotors, Stillen SC, Quaife ATB, Z1 Oil cooler, AEM Gauge Set, Galeforce gauge mount, Avant Garde M590 Hypersilver w/RE-11, TopgunZ A2A kit., ECUtek tuned by Seb: ROLL TIDE!

barncobob

I don't get it...we spend good $$ on a exhaust and then have to modify it to be useable

future370zzz

10 years ago I wouldn't have a problem with the drone.

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Joey370Z

I have full motordyne shockwave on my car with the ART test pipes and I have ZERO drone and all full quality exhaust. Well worth the money. Hemholtz design is even on the test pipes.

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2010 40th Anniversary 6MT | Motordyne shockwave catback | Motordyne ART test pipes | Stillen Gen 3's

future370zzz

Yeah, this was the next option for me. To switch to motordyne but the side branch option is a lot cheaper with the exhaust I already had.

If I could do it again, I would do motordyne. Nothing wrong with FI. Its on the list if I have extra funds.

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solteroblues

I went with aluminized because 304 would have cost 3x's the price and at that price point, I would have just gone with one of the other exhausts that already has the helmholtz, like the ARK grip.

MoulaZ

Digging up this thread in hopes someone could help assist. Read every page and like to get a little more confirmation.

Looking to do this mod to the new Invidia CBE I've installed (that I'm already regretting coming from a Motordyne CBE). It's droning horribly from 1900-2800.

At around 2000 RPM it seems to reverberate across three peaks, strangely 50hz apart... ~100, ~150, ~200.

Past this point 150 becomes the dominant droning frequency.

Photos attached of both occurrences.

According to the formula in this thread I get a length of 22.5"... but that seems quite small compared to the 28-30 I'm seeing thrown about.

Does this still seem right?

Speed of Sound / ( (frequency) x 4 )

1125 / ( 150 x 4 ) = 1.875ft > 22.5in

Attached Images

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	2017-06-07 07.26.13.jpg (168.0 KB, 64 views)

future370zzz

I think the best bet is to make the tubes easily adjustable for length. In theory we can crunch the numbers but you won't know until you try it. Exhaust systems are not created equal.

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MoulaZ

This was going to be my approach. It was already suggested earlier in the thread to have an adjustable style system with a clamp.

But still was hoping to hear my math was on point or missed something.

jmacf40

I love every note that my Fast Intentions non res exhaust makes. Even so called drone.