Abstract: Improvements in alkylation effluent flash vaporization systems used in processes of alkylating isoparaffinic hydrocarbons with olefinic hydrocarbons in the presence of acid catalyst and an excess of isoparaffinic hydrocarbons; improvements in heat sources used in such alkylation effluent flash vaporization systems, specifically utilizing hot and compressed isoparaffinic hydrocarbon vapors generally available in such systems from such sources as fractionation (deisobutanizer) overhead or vapor flashing processes utilized in cooling the reaction step or both; improvements in alkylation effluent flash vaporization systems which reduce the load on the conventional step of retrieving excess isoparaffinic hydrocarbons from the alkylation reaction effluent for recycle to the reaction step.