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VE Drone

hanson1128

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as title,
VE Auto drone issue when at low rpm, is it because of the Plastic things at the boot ( which spare wheel locate ) ??
I have been told by an Exhaust supplier, there is only VE have this problem occur due to dual exhaust just way too close to the plastic stuff and it's the only reason caused an Auto VE cabin drone when at low rpm, and it won't happen on other series of VE Holden / HSV. Is it true?

And as i known, some brand exhaust system guarantee not to drone before fit an aftermarket camshaft, for some decent camshaft it will still drone free but some other different size of camshaft will still caused drone. ( correct me if i'm wrong )
I have asked some difference performance shop but most of them comes with different advise.. its really confuse of it.....and....wtf?..

Drone a bit are still acceptable but badly Drone makes u wanna kill yourself, i don't mean 100% to get rid of it but try to reduce it as much as we can.
any opinion? Exhaust Brand? or do some Sound Barrier / Isolation or Sound Absorption work at boot ??

Please suggest me what you thought and any advise will be much appreciated.
 
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AD07

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Errrmehggggrd......english much????
Insulate the boot with bubble wrap, turn the radio up, and change the exhaust to a single 1 3/4 system......:idea:
 

PIR4TE

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It doesn't matter what fricken brand of exhaust, they all drone at 115hz, some are masked with 2nd, 3rd, 4th harmonic (noise) is all.
The cause is a natural harmonic which occurs due to the cylinder ignition interval (90º) that you can't modify or alter without changing the fundamental timing of the engine's mechanical equation. Yet without addressing / eliminating the cause of this 70db drone @ 116hz you will be constantly chasing butterflies around your car trim with Dynamat!
The solution is to interpost a wave in the exhaust that's exactly out of sync with the engine's sound wave, so they cancel each other out. A Helmholtz chamber (two capped lengths of pipe) provides the cancelling wave to the exhaust drone at certain frequencies.
You need to sample the drone using your smartphone, then use the proper mathematical formula to calculate the ideal-length of your capped pipes. I gave a line diagram to the local Midas bloke to install two of these Helmholtz pipes on my Xforce at the axle back before the muffler and have been totally drone-free for three years now.
The pipes are capped so it's a high pressure area, no exhaust gasses have anywhere to exit out, so no exhaust gas enters hence are cool to the touch even while other parts of the exhaust system are scalding hot.
Sound waves on the other hand travel through anything they can (same the reason Tri-Ys and 4-2-1 produce the best results for an engine's maximum smooth performance). Sound waves enter the mouth of the Helmholtz pipes in a pattern. Remember back to math class: sin and cosin? Picture that, for this example. So sound waves of a specific frequency (drone) enter and hit the "capped, sealed, end" and reflect back in the EXACT OPPOSITE SOUNDWAVE PATTERN ... mathematically, if you have a sin and the inverse of it, it turns into a flat line. Similarly, the "reflected back" sound cancels out sound waves trying to enter the mouth of the Helmholtz chamber once again.
Result? SILENCE. This does not take away from either performance or the great sounds of a performance exhaust (high velocity 4-2-1s with tuned transition to 3" cats punching out to 2.5" low carbon Xforce catback, in my case). It passively targets the drone soundwave (in Hertz) and totally cancels it out forever, leaving a drone free experience in the cabin of the car. Pure musclecar aftermarket performance exhaust sound, without any of the headache-inducing drone. What's not to love?
 

PIR4TE

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Errrmehggggrd......english much????
Insulate the boot with bubble wrap, turn the radio up, and change the exhaust to a single 1 3/4 system......:idea:

^^ Yes, look at the harmonics of your full exhaust - the ideal header dia for a stock VE to get max low to mid-range Torque and Hi RPM HP is 1.394", less than stock but total combined segment length is 35" (12" longer). But by all means go ahead and strap a short section of fire hose onto a garden tap if you want to impress your mates at the pub, but you can't complain that your exhaust drones, makes less power 95% of the time and sounds like an old boat with those expensive, signature 1 7/8" 4-1s.
 

2t4me

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It doesn't matter what fricken brand of exhaust, they all drone at 115hz, some are masked with 2nd, 3rd, 4th harmonic (noise) is all.
The cause is a natural harmonic which occurs due to the cylinder ignition interval (90º) that you can't modify or alter without changing the fundamental timing of the engine's mechanical equation. Yet without addressing / eliminating the cause of this 70db drone @ 116hz you will be constantly chasing butterflies around your car trim with Dynamat!
The solution is to interpost a wave in the exhaust that's exactly out of sync with the engine's sound wave, so they cancel each other out. A Helmholtz chamber (two capped lengths of pipe) provides the cancelling wave to the exhaust drone at certain frequencies.
You need to sample the drone using your smartphone, then use the proper mathematical formula to calculate the ideal-length of your capped pipes. I gave a line diagram to the local Midas bloke to install two of these Helmholtz pipes on my Xforce at the axle back before the muffler and have been totally drone-free for three years now.
The pipes are capped so it's a high pressure area, no exhaust gasses have anywhere to exit out, so no exhaust gas enters hence are cool to the touch even while other parts of the exhaust system are scalding hot.
Sound waves on the other hand travel through anything they can (same the reason Tri-Ys and 4-2-1 produce the best results for an engine's maximum smooth performance). Sound waves enter the mouth of the Helmholtz pipes in a pattern. Remember back to math class: sin and cosin? Picture that, for this example. So sound waves of a specific frequency (drone) enter and hit the "capped, sealed, end" and reflect back in the EXACT OPPOSITE SOUNDWAVE PATTERN ... mathematically, if you have a sin and the inverse of it, it turns into a flat line. Similarly, the "reflected back" sound cancels out sound waves trying to enter the mouth of the Helmholtz chamber once again.
Result? SILENCE. This does not take away from either performance or the great sounds of a performance exhaust (high velocity 4-2-1s with tuned transition to 3" cats punching out to 2.5" low carbon Xforce catback, in my case). It passively targets the drone soundwave (in Hertz) and totally cancels it out forever, leaving a drone free experience in the cabin of the car. Pure musclecar aftermarket performance exhaust sound, without any of the headache-inducing drone. What's not to love?

Highly informative post thanks - I just wish I understood it! (Maths is not my strong point!)

Excuse my ignorance hear, but I'm assuming that the measurements for where to put the helmholtz pipes and how long to make them would be unique each different brand/model of exhaust system??

Would it then need changing if further engineers were carried out?
 

PIR4TE

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Highly informative post thanks - I just wish I understood it! (Maths is not my strong point!)

I cheat, always use a calculator! I bought one specifically for tuning exhausts, an industry reference called PipeMax.

Excuse my ignorance, but I'm assuming that the measurements for where to put the helmholtz pipes and how long to make them would be unique each different brand/model of exhaust system??

To eliminate different sounds along the exhaust pipe you could have several cancellation chambers at different points along the system at various orders of harmonic resonance but that's practically what resonators / mufflers are there for.
For me the only issues to manage the sound waves are when reflecting back into the cylinder using header, collector (expansion pipe) design for performance; and the drone at the rear at highway speeds.
Measurement of the former specification requires some technical input (but I can help with that), whereas the bandwidth of drone resonance is +/- frequencies around 115 hz such that using a 4" sliding clamp on the end cap so you can cover (tune) it to suit 27" to 31". Like a trombone.
Best location is at the rear, axle back, for dimensional fit and proximity of exhaust to atmosphere.

Would it then need changing if further engineers were carried out?

As above not the Helmhotz chamber, but headers / collector yes.
 

2t4me

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Thanks again, I'll have to remember this post when I convince the minister for all things fun that they're needed!!
 

akidakix

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Doesn't the AFM system also contribute to the droning noise?

Sent from my HTC_PN071 using Tapatalk
 

bradizle

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your best bet is to get an exhaust from sureflo exhaust. They are KNOWN for non drone systems. greg (the owner) of sureflo has a AFM auto wagon . He is running a dual it ".

The system is very quiet at low revs.. it Passes the noise test requirements... .. although one stab of the accelator and its all over.
it really roars when given some stick...

here are some videos..


 
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phillmac

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Temp gauge read stone cold when reving the **** out of that motor. Some people should just drive old Camry's.
 
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