Helmholtz resonator exhaust chambers

[Vertigo]

Looking to cut down drone in my exhaust, and this looks like a good avenue to do so. I only really get drone around a certain RPM (2500-3000), so only a narrow range of frequencies (yet to measure).

Anyone made one? What formula should I be using to determine the chamber characteristics?

[Vertigo]

Have measured the frequencies that drone, appears to be around 96hz, with some also at 64hz, and harmonics of 96hz.

Also done some reading about how to go about designing it. Using this formula for the length of pipe needed:
L = (Vs / f) / 4
Where Vs is the velocity of sound, f is the target elimination frequency, and the 4 makes it a quarter wavelength, to lower the length needed - still targets the problem frequency.

Solving:
Vs = 340.29m/s
f = 96hz
L = 0.89m, or 89cm

This pipe should be the same diameter as the pipe its joining to, welded in at a right angle, and capped off at the other end. It doesnt need to be strait, a lot of people seem to use a 180 degree bend.

Ive seen designs where the neck of the pipe of of smaller diameter to the resonator chamber, but apparently the strait pipe design works well too.

[Lith]

Keep us up to date on how you get on. If you're getting that into it, it probably wouldn't hurt considering the temperature you expect the exhaust gases at the chamber to be and estimate your speed of sound based off that. 340.3m/s assumes speed of sound at 15c through air, the composition of gases in the exhaust allow similar speed of sound in similar conditions to air... I've not really worried about exhaust temps after they've travelled too far from the port, I'd say they'd have dropped a fair bit but I'd still not touch an exhaust tip - but just for interests sake If the temps are still near what they are when they enter the exhaust manifold then the speed of sound could be in the region of 600m/s which is getting very significant.

Most of the gases in the exhaust stream are likely to carry sound at +/- 10% of what air does all other things being equal so probably less significant but the temps "only" need to get over 80c (again I don't really know how much it loses in the system so haven't thought about it) to go past that level of error so may be worth pondering if you haven't already.

[Vertigo]

You are completely right re: exhaust temp and speed of sound.

Anyone know off the top of their head what the exhaust temp is for a stock 4AGE at cruising?

Also does anyone know if join location plays a factor in the cancelling characteristics?

[Flannelman]

EGT for 4age was about 700F on cruise (town) and 1200F cruise (100Km/h) and WOT