The 1KR-FE engine of the CityBug

The CityBug (107/C1/Aygo) is equiped with a 1KR-FE petrol engine from Toyota. The Toyota KR engine family is a straight-3 piston engine series, designed by Daihatsu, which is a subsidiary of Toyota.

The newly developed 1-litre 1KR-FE engine is one of the cleanest and most fuel-efficient petrol engines on the planet. The 1-litre, in-line three-cylinder DOHC engine (type 1KR-FE) employs continuously variable valve timing and optimised intake ports, generating rich torque in the low- to medium-rpm range. Developing a maximum output of 50kW/68hp at 6000rpm and a maximum torque of 93Nm at 3600rpm, the 1KR-FE delivers excellent acceleration under town use conditions involving frequent stops and starts. Featuring compact combustion chambers and an offset crankshaft, this engine employs resin-coated pistons and low-tension piston rings to reduce friction inside the engine. The highly rigid aluminium block and an oil pan that's also made of aluminium contribute to low vibration and quietness while substantially reducing weight, making the 1KR-FE an extremely fuel efficient and clean engine.

The 1KR series uses aluminium engine blocks and DOHC cylinder heads.
It also uses SFI fuel injection, and has 4 valves per cylinder with VVT-i.
The 1KR-FE is a 1.0 L (998 cc) version built in Japan and Poland.
Bore is 71 mm and stroke is 84 mm, with a compression ratio of 10.5:1.
Output is 50kW/68hp at 6000rpm with 93Nm of torque at 3600rpm. I found an overview about the combination of the revs per minute (rpm) and the speed (km/h) of the CityBug.

At 1000 rpm the speed is:
• 1st gear - 8,1 km/h
• 2nd gear - 15,1 km/h
• 3th gear - 21,91 km/h
• 4th gear - 27,96 km/h
• 5th gear - 33,78 km/ h

At 3600 rpm (max torque) the speed is:
• 1st gear - 29,16 km/h
• 2nd gear - 54,36 km/h
• 3th gear - 78,876 km/h
• 4th gear - 100,656 km/h
• 5th gear - 121,608 km/h

Switching gear (up) at max torque:
• 1st gear - 6700rpm = 2nd gear - 3600rpm
• 2nd gear - 5200rpm = 3th gear - 3600rpm
• 3th gear - 4600rpm = 4th gear - 3600rpm
• 4th gear - 4350rpm = 5th gear - 3600rpm

Switching gear (down) at max torque:
• 2th gear - 2000rpm = 1st gear - 3600rpm
• 3th gear - 2500rpm = 2nd gear - 3600rpm
• 4th gear - 2800rpm = 3th gear - 3600rpm
• 5th gear - 3000rpm = 4th gear - 3600rpm

The 1-litre 1KR-FE engine is one of the cleanest and most fuel-efficient petrol engines on the planet.