whats 50% power increase on an a12? 5 hp :)

I can only imagine what a longer inlet manifold length might add to
an A12 for economy and performance. If you can improve the low and
midrange further then there is better energy use and engine effort.

Could a single 1.5inch SU improve over a Hitachi? I often think about
making a long equal length inlet manifold with separate runners curving
over the rocker cover to the sparkplug side with a single su on the end.