Does anyone have knowledge of the maximum RPMs are Model T Ford's transmission is able to take?
Not sure of max RPM but have been to 4,500.
I think the racers back then used to cut down the flywheel to just a little larger than where the triple gears sits. With magnets on, I wouldn't like to rev higher than 2000 rpm for longer periods. The splash lubrication system would also become marginal at higher rpms.
Here's an older thread with some interesting numbers telling how high forces there are on the triple gear bushings when revving in low:
Quoting Ron Patterson/ Dan McEachern:
"If one calculates the reaction forces for a triple gear set transmitting 20 HP @ 2000 engine rpm, the load on a triple gear bushing/shaft is about 650 lbs. At 2000 rpm in low gear, a triple gear is spinning on the shaft at about 1300 rpm., (higher in reverse). The load on the bronze bushing under these conditions is about DOUBLE what most bronze bearing manufacturers recommend under the most favorable conditions for a sleeve bearing of this type. The majority of this load is a function of the square of engine speed, so if you are a T owner who just putts around in your car, you may never have problems. Granted, this is a worst case condition, but many T's are capable of putting out well over 20 HP, and are regularly wound up pretty tight on long steep grades or when trying to keep up with modern traffic when getting up to speed. Simply stated, at worst case conditions, the oil film in a simple journal bearing this size cannot support this large a load without metal to metal contact due to failure of the oil film."
More likely, would be how many rpm can the magnets take? The problems with the transmission are usually worn bushings or cracked drums. Or the bands can be worn out. If the bushings and drums are in good condition, not likely to be a problem with rpm especially if things are in balance. The magnets are also prone to cracks and the faster the engine goes, the more likely to "throw" a magnet.