there aint replacement for displacement..forced induction may give you some gains..so would other clever gizmos like methanol/water injection and MSD ignition. However mod gains are proportional to engine size...smaller engines will give you small gains when modded..
VVTi, VTEC, MiVEC, etc etc..are all fuel saving technologies..and you don't talk about fuel economy in real racing scene..
CNG engines can pack more punch however only if tuned and built right by an experienced engine builder..
for those looking mehran modding..get a hyabusa engine and gear box..these engine produce 500HP in turbocharged configuration and rev like anything.. you gonna have a mehran F1.