Thanks Krakatoa, I've made a lot of test and it seems i'm still can't understand the behavior of the Delta-V. Why my lv-909 (LF+Ox) have a better Dv than my NV-GX Emancipator (LH2) with a little fuel tank when it's the opposite with Very large Tanks ? (NB: for the larger tank i put 8xLV909 and 8xNVGX. With only one engine, the results are way more different LV909=7448 and NVGX=39986 )