Not really any such thing as 'race spec', even the clio cup cars race standard engines. Basically depends on how far you really want to go, and of course how deep your pockets are, but forged rods and pistons are a good start. Then you'd want to look at one-piece valves such as those by supertech. Then of course the cooling, airtec intercooler or similar, plus a turbo cooler to help keep coolant temps down.
Standard Megane 250 turbocharger can do 310bhp all day long, but you'll need 630cc injectors with the standard clio fuel pump, or an updated fuel pump. Then add megane 250 fuel rail with return line. And a 3" exhaust as standard clio diameter is a restriction.
Of course you can just fit a 250 engine and the standard pistons and rods will handle 360 lb/ft all day long so no need to forge.
And you'd want an lsd to put the power down.
Soon adds up, budget for 5k and expect to spend more.
Have a read of the Forced Induction section on here.
@Big Ben @L33 KUP