Haven't been around a lot and just saw this thread come back up.
The pipes are a slip fit into the elbows I used, at least two inches in. The band clamp was used so I could easily get it apart if something needed to be changed. Still need to make some supports for the ends, even though there's no movement to them.
Everything I heard is these work in a very small frequency range, pipe length is pretty picky. This spring I decided to add a couple of inches to the pipes (found some new calculations for length). It got even better now. I believe I'm at 26 or 27 inches (can't remember exactly).
If anybody is making these, just remember, drive the car until everything is up to temp. The temperature will change results a little.
If you are tuning for say 1900 rpms and use a 28.5" tube, it will help the drone at rpms just above and below that, but tune for the rpm where the drone is at its max.
I did download a spectrum analyzer, but not sure how good it was. Took readings before and after (both when everything was at operating temps). At first, I was unimpressed with the after readings. The analyzer showed only a small change, but by ear, it was huge.
Here's the new data I got and it seems pretty accurate:
Drone RPM--1/4 wave tube length
1700--32"
1800--30"
1900--28.5"
2000--27"
2100--25.75"
2200--24.5"
2300--23.5"
2400--22.5"
2500--21.5"
Since there are usually elbows involved, I just used a tape measure and checked the length going down the center of the tube.
If I wasn't already planning on replacing my exhaust, I would go this route. Here is a great calculator for this mod.
