Stop the Drone - Helmholtz Style

[SShift]

Great work!

[Roger Ramjet]

These pipes are 28 inches of 2.25 tubing. The result retains some growl up to about 1400 RPM then it just stops.

[SSizzle]

Originally Posted by BigRed585Lbs

Simply put, the formula for determining the length of a Helmholtz chamber used to knock out a drone frequency is:

1100 feet/second (roughly the speed of sound) divided by the target frequency you're trying to eliminate (in cycles/second) gives a full wavelength in feet per cycle. Divide this number by 4 to get a quarter wavelength (a much more convenient length to work with). Finally, multiply this wavelength by 12 to get the chamber length in inches.

Tap this length of pipe into the exhaust tube, making sure the other end of the pipe is capped off, and you have a Helmholtz chamber that takes the annoying frequency and bounces it back into the flow 180 degrees out of phase, knocking it out. The results: no more drone.

Right why didn't I think of that?!

[zepcom]

J-pipes at their finest. Nice work, OP.

Makes me think back to December 09 when I was frustrated until I found the secret J-pipe solution. I worked with BigRed585 and SOLO, and finally solved the drone problem on my car!

[BigRed585Lbs]

Had some fun with that one, didn't we!!!!

Oh, the sound; the sound!

[2010SLVRBULIT]

dunno..getting used to the droan..

[Frank Castle]

When I first looked at that I thought to myself no freakin way I'm doing that, but compared to getting $500-$600 x-pipes that seems the way to go.

[ssmike]

Originally Posted by zepcom

J-pipes at their finest. Nice work, OP.

Makes me think back to December 09 when I was frustrated until I found the secret J-pipe solution. I worked with BigRed585 and SOLO, and finally solved the drone problem on my car!

I'll have to take a look at them when we meet up! Did it affect the sound at all other than eliminating the drone?

[skar]

Seems like it would work. But to dampen the sound and changing the harmonic frequency Could you bolt or weld on a heavy piece of metal.
At work turning a tube or pipe on a lathe we wrap or fill it with babbitrite (sawdust and oil looks like clay) or use rubber straps. This keeps it from vibrating or chatter (singing)
I would think you could do the same on the muffler But need to fire proof it.

[zepcom]

Originally Posted by ssmike

I'll have to take a look at them when we meet up! Did it affect the sound at all other than eliminating the drone?

At the time I installed them, I had their quietest g8 kit (that still had drone without the J pipes)... so thus the J's did make the overall system slightly quieter. Around the g8 trouble area (1760-2000 rpm) it got nearly too quiet at the time.

No worries though, my "pre-alpha; proof of concept" J's were improved upon by SOLO once they saw how well it worked... now all their J-bend solutions are fully adjustable and much better designed than the one I started with.

I now have an unbalanced system, (not sure if this is offered to the camaro guys or not) which gives a "dukes of hazard"-like lope to the exhaust note, quite pleasing in my opinion. Additionally, Since March I've had the HF Cats which add ~15% sound volume.

On my g8 (and yes, I hope we can get together soon, ssmike!) I think it sounds perfect. Loud and aggressive when 'getting on it', yet subdued and responsible when cruising or driving normally. When I say "subdued" ... I mean drone-free, as well as not too loud where you couldn't hold a conversation with someone else in the car and the radio being on. It's all good!

[gahammerle]

Originally Posted by zepcom

I now have an unbalanced system, (not sure if this is offered to the camaro guys or not) which gives a "dukes of hazard"-like lope to the exhaust note, quite pleasing in my opinion.

Unbalanced - does that mean 1 j-pipe is longer than the other? If so, I may go and play with the adjustments on mine.

[zepcom]

Originally Posted by skar

Seems like it would work. But to dampen the sound and changing the harmonic frequency Could you bolt or weld on a heavy piece of metal.
At work turning a tube or pipe on a lathe we wrap or fill it with babbitrite (sawdust and oil looks like clay) or use rubber straps. This keeps it from vibrating or chatter (singing)
I would think you could do the same on the muffler But need to fire proof it.

J-pipes do more than dampen the sound. They elliminate it. Basically, since the J-pipes are sealed, consider them a "high pressure" area.

Let me back up a little bit here. Exhaust gasses are racing (excitedly) out to the end of your exhaust tips so they can reach the air, where the pressure is lower than where they came from (The combustion chamber and various exhaust components, actually!) ... so Exhaust gasses want to "get out" to an area of low pressure. Got it?

Okay, so since the J-pipes are sealed, no real "exhaust gasses" ever get into the J-pipes to begin with. To the exhaust gasses, the J-pipes are simply another wall that is not an option to exit from.

Sound waves are completely different. Sound waves can travel through just about anything... water, metal, etc. Sound waves are a byproduct of combustion engines. If you've ever heard "open headers" like on race cars or demo derby cars, you know what everything "really sounds like" right out of the combustion process. Normal factory stock exhaust systems are usually over-engineered to appease the 'transportation' type of person who does not like hearing engine noises. This is why enthusiasts upgrade to aftermarket exhaust components.

Drone is usually solved by a nearly silent stock exhaust system (over-engineered) ... and drone is the uncomfortable level of soundwaves, as they reverberate not only in the cabin but also in your eardrums.

What J-pipes do is allow the soundwaves to enter into the "mouth" of the J-pipes, and if you remember cosine/sine graphs from math class, you know what sound waves generally look like. Now the sound waves are inside this capped "tube" ... bouncing off each side in a certain pattern (Hertz rating) ... then BAM. they hit that cap at the end of the J-pipe. Now those sound waves are reflected in the exact opposite direction, in exactly the inverse wavelength pattern (effectively cancelling out that calculated soundwave pattern) and then at the "mouth" of the J-pipe, they safely exit back into the exhaust stream and out the rear of the car, now the inverse of what they were when they entered the J-pipe. The magic happens when the two inverses collide, within the J-pipe itself. This actually elliminates the sound that was calculated (or in other words, the exact overall length that you made the J-pipe).

If your calculation is wrong, you will not elliminate the sound.

This is completely different than "dampering" the metal to make the vibrations a different frequency, like you seemed to have suggested. While that works in some applications, the source of this drone is the engine itself, with it's specific engine harmonics. As soon as that stock exhaust system is replaced with a "performance" exhaust system, you get the nice rumble of a freer flowing exhaust system, however, now those engine harmonic traits (drone in certain RPM and engine load combination conditions) show their ugly head. J-pipes to the rescue!



That's the technology behind the J-pipes, in a nutshell. It works amazingly well, just a side effect of looking somewhat odd to someone who is expecting a muffler-looking apparatus under the rear of the car. They target the drone efficiently, without hardly any negative (silencing) of the performance exhaust sound that someone upgraded their exhaust system in order to hear. Win-win situation.

The proof of my claim of "high pressure area J-pipes" is that even after an hour of driving a J-pipe enabled car, the j-pipes themselves will be cool to the touch. This is because sound waves (only) are what enter and exit from the J-pipes, not exhaust gasses, and sound waves are independant of heat. Exhaust gasses, in contrast, contain a lot of heat, as the byproduct of the combustion process. Thus, be careful doing this test, as if you were to touch a part of the exhaust system that is NOT the J-pipe section after an hour of driving, you'd most definitely burn yourself. Don't say I didn't warn you!

Originally Posted by gahammerle

Unbalanced - does that mean 1 j-pipe is longer than the other? If so, I may go and play with the adjustments on mine.

Nope.

Unbalanced (as it pertains to the G8 offerings) means that there is no "connecting pipe" in front of the mid-muffler... meaning each separate bank of the car (side of the engine, consisting of 4 cylinders each) has it's own respective 'pulse' that goes through the muffler in an offset pattern. Compare this to using both hands at that "wack a mole" game, and offsetting each hand to be the opposite of the other. I know, stupid example. Anyways, at part throttle and idle conditions, these pulses are slightly noticable and are music to my ears. I do describe it as a "lope" similar to a mild cam sound would have. Slightly uneven offset of sound but not "misfire" or other bad issues. I compare to the dukes of hazard sound, if you've heard that, you have heard an offset or unbalanced exhaust system.

Both J-pipes are adjusted exactly the same. If one J-pipe was adjusted different than the other, the drone would only be 'half gone', in that only 1 j-pipe would be "tuned" to the correct frequency to cancel out the annoying drone, the other would be targeting a different frequency, and thus, would not be canceling out the troublesome drone.

Any other questions?

[Russell James]

Any exhaust companies planning on making such a thing for the Camaro?

Seems like there'd be a big market for it with all the droners out there.

[zepcom]

Originally Posted by Russell James

Any exhaust companies planning on making such a thing for the Camaro?

Seems like there'd be a big market for it with all the droners out there.

Yes. SOLO Performance has J-pipe solutions. I think it's mainly for the V6 camaro crowd though. From what I've read, the V8 camaro catbacks do not drone (and don't have J-pipes either). I could be wrong...