I swapped the wrapped B-section belts on a 1999 SCM FS 410 for cogged BX belts and saw an 8–10% amp drop at a 2 mm pass; pulleys are laser-aligned (≤0.1°) with a 420 mm center distance, tension set by 120 Hz belt frequency. Anyone else notice higher belt temps at the guard after this change, and what tension target are you using to balance slip-free start-up with bearing life on long runs?
On my 2000 Minimax FS41, BXs made the guard feel like a warm coffee mug, so I trimmed tension to about 105–110 Hz at a 420 mm span and still get slip‑free starts with a modest amp drop. I set it by the Gates frequency method and sanity‑check for no cold‑start squeal under a 2–3 mm bite: https://www.gates.com/us/en/resources/education/maintenance/installation-and-maintenance/how-to-measure-belt-tension.html. If it’s still toasty, make sure dust isn’t insulating the guard or the cover isn’t pinching the belt run.
Keeping 120 Hz after moving to BX probably over-tensions it — the notched belt’s lower mass means the same frequency = more static tension. On a 420 mm center I feed the BX mass into the Gates calc and land around 102–106 Hz, similar to @em_watson57; IR puts the guard about 45°C and bearing caps mid‑40s after a few 2 mm passes. They do settle in, so re-check warm and drop a couple Hz rather than cranking tension to cure a brief start hiccup.