Fixing exhaust drone with resonator tube (aka j tube/j pipe): how to calculate tube

[HORN HIGH ACES]

http://www.fordraptorforum.com/atta...lmholtz-resonator-no-more-drone-helmholtz.jpg
Not mine but the same thing

Thanks, that helps. Just want to confirm a couple of things on your set up since it's more similar to mine.


Does the resonator connect into the 3" pipe in front of the muffler and run parallel towards the back of the truck? If so, approx how far in front of the muffler?

Does the 26" length of the 2.5" resonator pipe include the bend or just the straight portion of it?

 

[ARH1956]

Thanks, that helps. Just want to confirm a couple of things on your set up since it's more similar to mine.


Does the resonator connect into the 3" pipe in front of the muffler and run parallel towards the back of the truck? If so, approx how far in front of the muffler?

Does the 26" length of the 2.5" resonator pipe include the bend or just the straight portion of it?

Mine connects behind the resonator directly into the 3" pipe and runs parallel to the muffler rearward. Mine measures 26" from the end of the tube measured along the outer bend where it welds onto the factory 3" pipe.

 

[DougF150]

Another Example

I have a 2001 F150 with the 4.6 that needed just a little more oomph, so i installed an SCT flash tuner and a 3" exhaust with a Flowmaster 40 series muffler. The sound was deeper and far from obnoxious, so it was perfect for a 62 yo. But, oh the drone I had created at 70 - 75 mph, and much of my driving is on interstates. The drone was so strong that it actually upset my inner ear enough to make me slightly nauseated. So of course I googled and learned about quarter wave resonance cancellation through the use of J-pipes. Folks, I admit I did not go through any calculations, but I was finding a lot of examples of people with v8s installing J-pipes inline before the muffler, and they were in the 26" to 28" range. So my friendly muffler shop, after much discussion about never having heard of such thing, but did look at the many photos I had printed off the Internet, basically said it's your money and made the installation that you see in the pictures. I am happy to say that I lucked out and the cancellation of resonance is perfect for me, because the drone was instantly gone at all rpms.

 

[Steelhead]

I have a 2001 F150 with the 4.6 that needed just a little more oomph, so i installed an SCT flash tuner and a 3" exhaust with a Flowmaster 40 series muffler. The sound was deeper and far from obnoxious, so it was perfect for a 62 yo. But, oh the drone I had created at 70 - 75 mph, and much of my driving is on interstates. The drone was so strong that it actually upset my inner ear enough to make me slightly nauseated. So of course I googled and learned about quarter wave resonance cancellation through the use of J-pipes. Folks, I admit I did not go through any calculations, but I was finding a lot of examples of people with v8s installing J-pipes inline before the muffler, and they were in the 26" to 28" range. So my friendly muffler shop, after much discussion about never having heard of such thing, but did look at the many photos I had printed off the Internet, basically said it's your money and made the installation that you see in the pictures. I am happy to say that I lucked out and the cancellation of resonance is perfect for me, because the drone was instantly gone at all rpms.View attachment 93094

View attachment 93095

View attachment 93096

Any change in the volume or loudness?

 

[cohunter14]

I actually added a a hemholtz resonator onto my MBRP turndown exhaust (with resonator) last week. Originally we used a 3" x 29" pipe but found it to be too long and was effective at too high of an RPM or be useful below 75mph and made the exhaust overly quiet overall. After incrementally shortening the length, i also found that 26" was decent for my setup as well for 60-75mph (TX highway speeds) but an inch or two shorter would probably be ideal.
I definitely agree that anywhere in the 24-26 range will probably get you where you need to go.

@Chinmasterflex I tried sending you a private message regarding this, but I don't think you got it yet. So I apologize for bringing up an old thread. I'm wondering if you stayed at 26" on this or decided to go shorter. Also, where were you having the droning issues RPM-wise? Do you have the MBRP turndown system with or without the resonator in it? Feel free to PM me back if that's easier.