From what I understand, the Harmon Rocket II [ZK-TWU] is essentially a modified RV4. This particular aircraft has a slightly modified Lycoming IO-540 in it. From memory, it went through around 90 litres of Avgas from Queenstown [NZQN] to Wellington [NZWN]. This would make it more fuel-efficient than a Cessna 172 over the same distance [and a lot quicker with a comfortable cruise approaching 200 knots!].
Enjoy!