oh and while i'm asking for help, it's hard to ignore the super simple snowmobile CVT.
if you look at snowmobile drag race videos they launch off the line and within a split second they are at the same RPM for the whole run.
they do look like they have about a 3:1 ratio range depending on the exact model. they do technically allow slip to acheive a ratio over 3:1 but that causes heat really quickly so we don't really want to depend on it.
if we run these numbers though the simplest setup but still a worse case scenario: engine only likes RPM changes from 90% to 100% (it's probably wider, but i just don't know) assume no beneficial CVT slip and assume a desired top speed of 110mph.
for 12,000RPM to equal 110mph @900rev/mile i need a final drive of 7.2:1 let's just assume that we stuff that all in the differential (that's not going to happen, but it keeps this simple and it's just going to be a question of adding a 2nd reduction in front of the diff)
minimum "full power" speed would be 10800rpm turbine with 3:1 at the CVT and the same 7.2:1 diff would be 33mph. this is slow enough to take even really tight hairpins without needing to disengage the turbines.
unfortunately, the car would absolutely suck at getting to 25 or even 30mph. but that's where the pony motor could come in.
let's say i drove a small diesel motor through some normal transmission probably an auto to keep everything simpler. and then the trans output into a box and the box would go to a 3.55 differential out to the wheels.
the box would contain a small ratio and a clutch to couple/decouple the turbines the clutch would simply be controlled by a high/low speed switch (again, oversimple but we can worry about hysteresis later)
the turbine inputs would be from two belt CVT clutches (because it's MUCH cheaper to get two smaller HP CVTs than one that can handle the power from both) but the inability for the driven wheel to drive the drive wheel on that setup would mean i'd need some kind of turbine starter still. not the end of the world.
it's a super simple solution but it's absolutely critical that the belt CVTs maintain a very narrow RPM range. i should contact some of the aftermarket manufacturers of snowmobile clutches and see if anyone is willing to talk about technical specs beyond the intended application.