assalam o alaikum n below are the specifications for both of these engines ..
D15B 3-Stage VTEC
Bore and Stroke :75,0?84,5 mm
Displacement : 1,493 cc (91.1 cu in)
Rod Length : 137 mm
Rod/Stroke : 1.62
Compression : 9.3:1
Power : 130 PS (96 kW; 128 hp) at 7,000 rpm[6]
Torque: 139 Nm at 5,300 rpm
VTEC 12-valve to 16-valve switch over : 3,000 rpm (below such engine speed, the engine is operating in 12-valve mode)[7]
VTEC high cam switch over : 6,000 rpm
Redline : 7,200 rpm
Valvetrain : SOHC, four valves per cylinder
Connecting rod length : 137 mm
Connecting rod big end diameter : 48 mm
Fuel Control : OBD2a
Head Code : P2J-07
ECU Code: P2J (small case ECU)***
R18A1
Displacement: 1,799 cc (109.8 cu in)
Compression: 10.5:1
Bore & stroke: 81.0 mm ? 87.3 mm (3.19 in ? 3.44 in)
Power: 140 PS (103 kW; 138 bhp) @ 6300 rpm (Japanese Spec)
Torque: 17.7 kgf?m (174 N?m (128 ft?lbf)) @ 4,300 rpm
VTEC for economy 1,500-3,000 rpm
As you can clearly see from the stats above that R18 should be more fuel efficient and more powerful then D15B VTEC but I have heard and also experienced that D15B VTEC can easily beat R18 and its also more fuel efficient? any senior members on it that why it happens? and do you also experience the same?