You're not going to get it.
JDM F6A turbo Jimny, similar looking to the PKDM Potohar, gets me 6.5km/L. No more. Not possible.
Heed this advice. Consider the size of the wheels, the small ratios in the Jimny 5MT, the transfer case ratio, and the final drive. I HAVE to get my Jimny up to 5500rpm, otherwise it doesn't overtake anything and doesn't build momentum. Forget about the turbo lag.
Disagree.
Perhaps a Suzuki M13 (Swift, newer Jimny), M16 (Liana), M18 (Liana), G13 (Baleno iirc), or G16 (Vitara) swap will get you better fuel consumption. Those engines are naturally-aspirated and might produce enough torque low down to take off from a standstill in 2nd or 3rd gear. But that's it as far as easy bolt-on swaps are concerned.