Any C172SP 180 I've flown cruised at 115Kts at 8usg/hour low level.
M,N and P models I've flown struggle to manage 100KTS at 8 imperial GPH so there is a substantial difference. Of course most of the older ones are only 140-160BHP.
There must be other differences because I have some time in the Cutlass which can only manage 120kts. It is a C172 180 with retracts and constant speed prop. It used nearly 10 USG/Hr.
Fuel injection definitely improves economy. On the C182 I've been flying recently it is worth 2 Imperial GPH. This will be partly due to being able to lean it more aggressively without it shaking itself to pieces!
D.O.
Edited to add:- The C172SP's I've flown all had around 850lbs useful load. 6 hours and 515lbs for bodies or cargo.
Last edited by dont overfil; 18th October 2014 at 15:11.
Reason: And another thing!