Big engine with small heads causes a different problem so the 2 hp/cfm rule might not apply. There is also a velocity rule that has to be obeyed. If the velocity gets too high or is too low then the engine won't make 2 hp/cfm. Big engine with small heads has high velocity while a small engine with big heads has slow velocity. Either too fast or too slow will kill off the performance.
there is no issue at all with having big heads on a small motor... as a matter fact you can't get a big enough.. Bob books small block mopar Motors at 400 cubic inch... have heads flowing close to 500 CFM....it is all about rpm ...and at 3hp per cubic inch.. I would say very impressive
