Original sentence: The designed thrust/weight ratio of SABRE ends up several times higher—up to 14, compared to about 5 for conventional jet engines, and two for scramjets; whilst giving very good fuel efficiency—about 3000 seconds (3000 lbf·s/lb or 29 kN·s/kg)
Edited sentence: The designed thrust-to-mass ratio of SABRE ends up several times higher—up to 14 N/kg, compared to about 50 N/kg for conventional jet engines, and 20 N/kg for scramjets; whilst giving very good fuel efficiency—about 3000 seconds (3000 lbf·s/lb or 29 kN·s/kg)