VOLVO engine type B18 or B20 are one of the BEST engine that had been build for tune it up, up to... the sky is the limit.
Between 120HP to 280HP all by mechanic way!!! so, make your mien what do you like to got out and what your bought for it. The basic way, working on the engine head, port it out plus some worm Camshaft. For the amount of Euro 2500.00-3000.00(in Europe) you may got B18/20 with ~160HP and ~28Kgm !!!!! by use 2xSU carburetor, this engine run perfect from the bottom rev up to 9000rpm, so it's drivable in the city and outside highway. put 2xWeber 45 and get 185HP and....
I drive Amazon B18B with ~130HP
DG