The RD-170 engine was designed during the 1970's to power the liquid booster for the Energia launch vehicle.  After the N-1 Moon Program ended in failure, partly due to Korolev's decision to use 30 medium thrust NK-33 engines on the first stage, Glushko re-doubled his efforts to develop a high thrust engine which could be used to launch heavy payloads.  The result of these efforts was the RD-170, a 1.75 million pound thrust liquid oxygen / kerosene engine.  Today, the RD-170, which has slightly more thrust than the F-1 which powered the Saturn LV, is the highest thrust engine ever flown on a space launch vehicle.

Recently, the RD-170 has been marketed to western vehicle manufacturers by Pratt & Whitney as part of their relationship with NPO Energomash.  Two variants of the RD-170 exist.  The RD-170 / -171 powers the first stage of the Zenit 2.  It was also used to power the Energia liquid boosters.   The RD-173 is a higher thrust version developed to power the three stage Zenit 3SL.