I'm having trouble finding a US dealer selling the 13 one online. The Australian distributor is hopeless in getting stuff in. I would really love to know what has been changed as I have just ordered the 144 kit.
I bought my Fatty and TurbineCore2 (for 2013 WR125) directly from FMF. The online stores I talked to could not tell me much about the differences between model years of the Fatty. FMF seemed "guarded" about the differences, but I went ahead and bought the '13 pipe.
I'll try to take some measurements of the expansion chamber section of my Fatty and OEM pipe. I'll post the data under this thread. I'm curious how they differ.
EDIT: 2013 OEM pipe vs. FMF Fatty
UPDATE: Below are the measurements of my FMF Fatty (#025163). Measurements were made at 2 inch intervals, beginning from the silencer end. I used a waxed thread to measure, then compared the measured length to a tailor's tape. Treat measurements as APPROXIMATES. It was a PIA trying to keep the thread 90degrees to the chamber's axis.
9.8 cm @ Silencer end along Right edge of weld bead
17.2 cm @ 2 inches (")
24.5 cm @ 4"
29.8 cm @ 6"
33.8 cm @ 8"
36.4 cm @ 10"
36.3 cm @ 12"
35.0 cm @ 14"
32.2 cm @ 16"
30.6 cm @ Header end along Left edge of weld bead.
I have no idea what the inside dimensions are at my measuring points. The Black Art of 2-stroke expansion chamber is too much for me to grasp. I hope the numbers help. At least you have a reference point now. Hopefully others will chime in.
I didn't measure my OEM pipe. It's 110 F in my garage, and I wussied out.
UPDATE 2: OEM Pipe - installed
10.0 cm @ Silencer end along Right edge of weld bead
17.8 cm @ 2 inches (")
25.2 cm @ 4"
30.4 cm @ 6"
34.2 cm @ 8"
36.5 cm @ 10"
36.5 cm @ 12"
36.0 cm @ 14"
32.6 cm @ 16"
(Not measured) @ Header end along Left edge of weld bead.
Header section - OEM (Fatty)
[not measured a the 18, 20, & 22 inch locations because mounting bracket]
21.2 cm (20.6) @ 24"
18.8 cm (18.6) @ 26"
17.0 cm (17.0) @ 28"
16.0 cm (15.7) @ 30"
15.0 cm (14.9) @ 32"
14.2 cm (14.2) @ 34"
Visually, the OEM vs Fatty seem very close. Dimension wise there are some differences, but seam/weld bead heights did influence my measurements (as well as my caveman method). The overall length of the Fatty is 45-1/4" . I'll measure the OEM when I install the Fatty.
My conclusion after this drill: The FMF Fatty sure looks purrty!