Quarter wave tubes

[SkurdalenFox]

Has anyone here developed an effective pair of quarter wave tubes/quarter tube resonators for the exhaust side on a five liter engine?

[coupe]

Are you talking about cancelling out unwanted frequencies?

Heimholtz resonance (http://en.wikipedia.org/wiki/Helmholtz_resonance)

I have thought about tapered mufflers (voight tubes), but I have never built one. Also thought about staggering the position of the mufflers...fore and aft of one another, but space limitations might be an issue.

You tired of the flowmaster drone too Jim? :D

[SkurdalenFox]

Yes, I'd like to try to cancel the 2000 RPM drone.

I am going to weld in flanges on the exhaust pipes so that I can put quarter tubes (perpendicular to the main tubes, obviously) between the axle housing and the gas tank. I plan to use slip-fit tubes so I can experiment with the length.

I expect a few problems: First, the exhaust temp. fluctuates, altering the speed of sound.

Second, the exhaust pipes are different lengths because I'm using unequal length headers. I am worried about this because it may be hard to tell which side is still droning. I may need unequal quarter tubes.

Also, It's probably a range of frequencies I'd like to cancel rather than one. I was thinking I could angle the "cap" on the end of the quarter tube to cover a wider range.

Also, since the frequency I'm trying to cancel is rather long, I don't know if I can fit long enough quarter pipes under the car to fully attenuate the drone.

[militarymustang88gt]

just put an h pipe on with a pipe going at a 45 from the cross over tube to the passenger side muffler. that should cancel out about 90 percent except at higher rpm like 5000+ but i dont think you will be cruising at that speed.

[coupe]

Saw a writeup somewhere with those tubes Jim. They were in front of the gas-tank and tucked up out of the way...might need to have a set of hangers to hold the ends of the tubes, but it should work.

[SkurdalenFox]

I don't suppose you recall where you saw this write-up.

Anyhow, I've got some more body work to do on the car before I start this project, but I'll let y'all know how it goes.

Reproduction fenders absolutely suck!!!!!!!!!

[SkurdalenFox]

Basic formula is: speed of sound = wavelength * frequency, which means

wavelength = (speed)/(frequency)

Quarter wavelength = wavelength/4 (as one would guess)

Speed of sound is from

http://www.sengpielaudio.com/calculator-speedsound.htm

(obtain speed from deg F, and in ft/sec)

Engine speed of revolution given as 2000 rev per min which (when divided by 60 sec/min) is 33.33 rev/sec

Firing frequency = (Number of cylinders)/2(four cycle engine) with V8 = 4

So exhaust fundamental frequency is 33.33 * 4 = 133.33 or about 134 Hz

So quarter wavelength = (1520(speed in ft/sec)/134) * (12"/ft) / 4 = 34", for 500 deg F at 2000 rev/min.


I'm just guessing at the EGT. Anyone have a better guess? I was thinking of putting the tubes after the mufflers. Car is a five liter 92, no cats.

[coupe]

Aft of the mufflers, I think the temps are a bit lower than 500º or so I seem to recall. :think: I tested it with a thermocouple back in college for a plastic tailpipe design (yes, you heard right)...and something tells me it was lower. WOT might be up there, but that's not where you're after the noise cancellation anyway. I don't have a thermocouple handy, but your calculations look spot-on! :nice: Cool thread.

[SkurdalenFox]

Ah, lower temperatures is better- shorter tubes.

[Purple1995Pony]

Also thought about staggering the position of the mufflers...fore and aft of one another, but space limitations might be an issue.

You tired of the flowmaster drone too Jim? :D


This is how the mufflers are setup OE on SN95's ( and Foxs too I think)for that reason. Most aftermarket H or X pipes don't stagger the connections so ...dronnnnnnne. Check out a stock H pipe to see.

[SkurdalenFox]

This is how the mufflers are setup OE on SN95's ( and Foxs too I think)for that reason. Most aftermarket H or X pipes don't stagger the connections so ...dronnnnnnne. Check out a stock H pipe to see.

The H pipe has nothing to do with it for a number of reasons.

High frequencies have short wave lengths, low frequencies have long wave lengths.134Hz is 100.7756" even at room temperature. 134Hz is pretty long and wide. It's probable that the muffler is already in the 134Hz range. Moving it a few inches isn't going to get it out of or into the 134Hz range. If the muffler is completely in the wrong spot there isn't enough room to move it into the right spot. Further, even if I could put the muffler in exactly the right spot, The muffler DOESN'T have tuning for the 134 Hz frequency. I could put the muffler anywhere, and it still wouldn't attenuate the 134Hz frequency.

Assuming the stock mufflers did not drone, I doubt it had anything to do with where they were and far more to do with what they were.

[Purple1995Pony]

I don't think IMHO, frequency has much to do with a matched set of mufflers. If the sound is not in sync between the 2 the (sound or frequency if you will, gets to the mufflers at different times) drone "seems" to disappear. A split second difference will change the sound even if it's very little.

[SkurdalenFox]

Fundamental Frequency is 134 Hz. C = 380 m/s. Lambda is 111". Quarter wave is 27.75" An inch here or there is meaningless.

It's like walking across Iowa. You go a long way, but there isn't much of an elevation change.

[coupe]

It's like walking across Iowa...
:lol: Boy is that the truth.

The unequal length of the H-pipe is recovered with one short and one long flowtube. The mufflers on every mustang I've seen have been side-by-side (unless it was hacked up at a muffler shop).

The drone has to do with the length of pipe...different lengths give you different eigenfrequencies, which can be amplified or diminished by mufflers (think Flowmaster or Super Turbo). The heimholtz chambers can change the frequency where the thing drones...or cancel out certain frequencies.

[SkurdalenFox]

(think Flowmaster or Super Turbo).

Ya, think really crappy helmholtz resonators. :)

Assuming the stock exhaust system didn't drone, do you know how FoMoCo did it?

The optimist in me wants to believe that they had some trick resonator in the muffler. The cynic in me thinks they just had some highly restrictive design that pulled all the energy out.

Lots of good stuff here in -
http://naca.central.cranfield.ac.uk/reports/1954/naca-report-1192.pdf