well if its a four cylinder twin cam then the specifications are a little different than polecat described....
without knowing the ID of the engine, (fiat, lancia, from a 131 or a Beta etc)
bore...84mm
stroke...90mm
compression ratio (probably) 8.9:1
output (between) 112bhp @ 5600 (132) and 119bhp @ 5500 / 130.5 lbft @ 2800 (lancia beta)
these are quoted outputs for carburettor engines, naturally aspirated. (also available in Volumex (supercharged) form
there are also a couple of variants, ie late injected cars and also vehicles with a "reverse" direction flow.... the head was reversed on the block putting intake/exhaust on opposite sides to "normal"
there are also many variants of cylinder head, different valve sizes, port sizes and camshafts from the factory.
If you have an engine ID or type (found stamped above the oil filter mounting block) then I may have more information for you.
If you want more output, how much money do you have to spend???
To build a 150hp output engine is one figure, but to go past this, its about 20% more money for every 10hp, so a 200hp output engine will be about double the price, naturally aspirated (but is acheivable and driveable in a road car) if you want to turbo the car, lots more $$$ but lots more ponies too.
16v heads from the late type engines (tipo, integrale) fit the early blocks, but need a fair bit of fiddling to get everything right..... check out this site
http://www.beardmorebros.co.uk/website pages/new_project_engine_page1.htm
for more ideas....
SteveC