custom exhaust questions got a drone from 3-4K rpm
 

Made a custom exhaust on my car downpipes are 3" and merges into a 3.5" exhaust i got a annoying drone/rattle between 3-4K rpm only. I already have a Vibrant Muffler and a inline 3" muffler. I was thinking adding 2 glasspack bullet mufflers closer to my downpipes one on each downpipe before the merge. Do you guys think that would get rid of the drone/rattle can noise?

Re: custom exhaust questions got a drone from 3-4K rpm
 

??? anyone

Re: custom exhaust questions got a drone from 3-4K rpm
 

maybe post a pic so we can see what you have done and give some advice

Re: custom exhaust questions got a drone from 3-4K rpm
 

Supposedly, glasspack type mufflers are only good at muffling higher frequency sound waves:
http://www.enoisecontrol.com/related...rrier_wall.pdf
Might want to look into a branch resonator.

Re: custom exhaust questions got a drone from 3-4K rpm
 

ill be making a side branch resonator then, seems like the best choice, My engine is 2.7L twin turbo and the rpm drone at 3-4K rpm is a killer cant stand to drive the car anymore.

Should i make my side branch resonator out of pipe with a cap on it or pipe to resonator with a cap on it.

Re: custom exhaust questions got a drone from 3-4K rpm
 

here is a picture of my exhaust since then i have added another 3.5 Muffler right where the long piece of straight pipe is

Re: custom exhaust questions got a drone from 3-4K rpm
 

Honda used a Helmholtz resonator on the S2000 to deaden drone. It's just a short piece of capped pipe welded perpendicular to the exhaust. You could try that. I'm not sure how long or what diameter it would need to be to fix your problem though. Could be worth looking into.

Tim

Re: custom exhaust questions got a drone from 3-4K rpm
 

^ That piece is acoustically tuned to take care of the resonance of the stock exhaust. Without high tech audio and a good bit of know how he really has no hope in making that. Both width of the pipe and length of the pipe are crucially important in cancelling the drone he is targeting.

Re: custom exhaust questions got a drone from 3-4K rpm
 

The setup you have has long straight sections. The long straight sections are "tuned" to particular frequencies. I would install a resonator in the middle of the longest pipe.