In this research paper the effect of injection pressure is investigated on a nanofuel sample compared with its basefuel blend. Waste cooking oil methyl ester and diesel blend used are in the ratio of 20:80. Magnetite nanoparticles are dispersed in the B20 blend using a probe ultrasonicator. Basefuel B20 and nanofuel with 100 ppm of magnetite is tested and compared at three different injection pressures 200 bar, 220 bar and 240 bar. The results show that BTE increases by 1.3% when injection pressure is increased from 200 bar to 240 bar. BSFC reduces by 3.2% when injection pressure is increased from 200 bar to 240 bar. Among emissions, the NOx value shows a 59% reduction, unburnt hydrocarbon emissions reduce by 35% and smoke opacity is reduced by 30% when injection pressure is increased from 200 bar to 240 bar.