My 86 1.5hp Cobra ZA came factory with the 13/77T first gear, but the bottom end was trashed so i never got to run it. I bought a 2hp parts maxi with a ZA on it and I flipped 2nd and put the 13/77 first gears in it. First gear was quicker off the line but engine rpm maxed out around 13mph, which is about where the flipped second starts to engage, with stock 18/40 sprockets anyways.
I wouldn't consider the 13/77T first gear a "restricted gear" setup, since second gear ratios are all the same. It's just a lower 1st gear setup to get it off the line quicker and up the steepest hills when compared to the 16/70T first gears. Either way, i still think it would fall way short of the powerband of most pipes once it would shift to second.
Ken, Which do you feel works better with your polini/estoril, 13T or 16T?