I had a a 99 vitz in past , kept it for 2 years , it doesn't feel underpowered .
But last week ,i drove a friends 2005 new shape vitz ,no CNG, with AC ,city drive ,i kind feel, it was little sluggish.
As newer vitz has a 3-cylinder engine ,previous one had 4-cylinder
so on papers new vitz is slower than older model vitz, but newer vitz is fuel efficient
The 1SZ-FE is 1.0 L . Bore is 69 mm and stroke is 66.7 mm, with a compression ratio of 10.0:1. Output is 68HP (51.5 kW) at 6000 rpm with 95 Nm of torque at 4000 rpm .
Vitz 2005 onwards
The 1KR-FE is a 1.0 L . Bore is 71 mm and stroke is 84 mm, with a compression ratio of 10.5:1. Output is 68 hp (50 kW) at 6500 RPM with 93.0 N·m of torque at 3600 RPM..