Donmaximo

Been researching a way to eliminate drone in my V8 Colorado (5.3, headers, 2.5” duals all the way back w/ dual Magnaflows).

Ive seen it asked here, but no real answer. Does it make much of a difference if the resonator tube is before or after the muffler? I don’t have much room after the muffler, but plenty ahead of it.

rbiron2

^ before or after it doesn't matter. I did it before.

Bring up the thread again, but for good reason.... this worked flawlessly on my truck when I had the x-pipe but now I want to run true duals.

So how would these calculations be affected if one were to run a true dual setup? Each exhaust would technically be run off of only one bank of cylinders thus it would be 2 pulses/rev?? I just want to make sure I get my tube length correct!

Mark Johnson

iTrader: (1)

OK- having gone thru the math with my drone starting at 1200RPM I'm arriving at a 27" tube for the Helmholtz resonator. Question is- will it only work at 1200RPM? As the drone carries to 1900RPM. would I need like another 24" piece in the system as well...……….

rbiron2

I was targeting 2000 RPM, true duals, did a 25" piece on each pipe and it took car of ALL of my drone. Truck is still loud when I get on it (just what I want), but no drone

@2001 Sierra I think you will be fine, the frequency cancellation doesn't just occur at a one specific RPM, it perfectly cancels at the target RPM but it slightly affects other rpms as well. It not just a yes or no thing, its a yes at the target rpm and a sort of at other rpms near the target, if that makes sense.

Donmaximo

Is 25" the total length including any bends, or just the length of the straight section after the bend?

Mark Johnson

iTrader: (1)

Yeah- hey, that is a good question...………..

rbiron2

Including the bends

Mark Johnson

iTrader: (1)

Well guys, I did it. Made a J pipe; 2" diameter off the 3" diameter tailpipe- and DAYUM what a difference; it tightened up the tone and cancelled out/ softened the drone. Hands down the best enhancement to an aftermarket muffler. I'm not embarrassed anymore to gently accelerate from 900rpm rollin up the mainstreet of the neighborhood...………...

Donmaximo

Finally got around to building resonator tubes this weekend.

I calculated a length of 28.1", so I built them as close to that as I could. I started with a mandrel U-bend, which I cut in half, and welded on at 90deg to the exhaust, then added a capped extension to get them to length. I mounted them on either side of the transmission as I have no room anywhere behind the mufflers. This is really the only spot I can see that they'd fit. My exhaust is 2 1/2", and I built the resonator out of 2".

Didn't make a noticeable difference at all. In fact, my wife thinks the drone got louder. Not sure why it didn't work for me and has worked so well for others. Its a dual system, with a H-pipe before the mufflers (after the resonators). Does it make a difference in the length of the resonators are before the exhaust crossover?

Not sure what I'm going to try next. This thing is obnoxious at 17-1800 RPM, especially under a light load.

Jeebalow

iTrader: (3)

Did you use 8 cylinders or 4 for your calcs? As far as the resonators go, they can only see pulses from 4 cylinders since they are before the crossover. Try recalculating with 4 cylinders instead of 8 and give that a shot.

From a quit calc I get 28.9" for 4 pulses/rev (8 cylinders) and double (57.87") for 2 pulses/rev (4 cylinders)

Edit- I know someone said they had simplified the formula, but I took it a little further.

For speed of sound = 343 m/s
Length [in.]=405118.3/(RPM*#Cylinders)

For speed of sound = 400 m/s
Length [in.]=472441.2/(RPM*#Cylinders)