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Old 04-27-2008, 04:11 PM   #1
SkurdalenFox
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Quarter wave tubes

Has anyone here developed an effective pair of quarter wave tubes/quarter tube resonators for the exhaust side on a five liter engine?
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Old 04-27-2008, 06:49 PM   #2
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Are you talking about cancelling out unwanted frequencies?

Heimholtz 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?
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Old 04-27-2008, 08:20 PM   #3
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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.
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Old 04-27-2008, 09:09 PM   #4
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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.
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Old 04-28-2008, 07:36 AM   #5
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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.
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Old 04-28-2008, 04:02 PM   #6
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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!!!!!!!!!
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Old 02-09-2009, 03:22 PM   #7
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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.
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Old 02-09-2009, 03:32 PM   #8
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Aft of the mufflers, I think the temps are a bit lower than 500 or so I seem to recall. 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! Cool thread.
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Old 02-10-2009, 09:56 AM   #9
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Ah, lower temperatures is better- shorter tubes.
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Old 02-10-2009, 10:27 AM   #10
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Quote:
Originally Posted by coupe View Post
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?

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.
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