Well I can tell you that my Tranzact pro nitro brake was set at 170 psi for use with a 904. The instructions clearly recommend either a 3.8 or a 4.2 the line pressures are set higher for a 904 because it has less clutch surface than a 727. That increased line pressure speeds up the application of the front drum aggravating the shift overlap.
Increasing the spring pressure and plate clearance in the front drum
Is done to slow down the piston application and give the band more time to release.
Paul Forte of Turbo action sets his brake at 190 psi and he recommends a 3.8 lever. The band width has nothing to do with it.
I have the widest band made for a 904. This band is not usually recommended any more because the apply lugs are not centered
and causes uneven wear. At these kinds of pressures clamping force
Is not an issue for the bands. Harshness and speed of apply/release
Is the problem. Afaik
