Well this is a sore point that keeps on coming up time and time again on this site.
I know John Taylor claimed that 200hp at the fly was what he got from his A15, 1600cc knife edged crank, big valves and ports roller rockers, motec and 50mm quad throttle bodies 54/86 cam. It had the best of the best. Translating that to bhp it had 125rwhp. It probably would cost around 10 grand to build in todays dollars. With the same money you could get around the 180rwhp out of and aspro SR20.
It is possible, but a budget racer like me just does the figures and i have to go mutlivalve for bang for your buck horsepower.
Anyway I will put my SR in and hopefully that will translate to better track times as the SR should have better torque and drive out of the corners. (fingers crossed).
Anyway back to original question 100flyhp is easy for an A15 on a tight budget.