Corrie...tell me more
What turbo?
What injectors?
Lance, it is basic, for x hp you need a certain amount of air from the turbo to feed the engine. The air/fuel ratio MUST stay workable. The injectors must be large enough to lower the A/F ratio to 11:1 on full boost at revs, to keep the engine cool so that it do not detonate. So x amount of cc/min can make y amount of power.
More than one guy reports that the QVs runs hot when pushed to the maximum boost at revs. That means om the injectors can not deliver enough fuel to cool the combustion chambers. One way is to add an injector in the induction, even if it is the easy way, that may? work against the direct injection principle of the engine. So the injectors in the engine must go up one size.
Go search the dyno chart I posted long ago for my 145, or Hennie's. Look again at the torque curve, once the boost is up torque stays on the same level to the redline. Compare with various QV curves. At revs the engine is taking more air away than the turbo can delivers, so pressure drops and so the torque. It is the factory's way to protect the engine and the cast manifold keep the tuner hands off. The easy way is to cut the manifold above the turbo and weld a std turbo flange onto it. Now you can fit any turbo you like. I know a T3/4B will do the job, but the new RS serries Garret turbos are more efficiant. This will emphasize the larger injectors even more.
Next stage is different cams with a higher lift is needed. Research the spares available for Lancia Integrales Std lift for them is 8.6/7.5mm (60% higher than the QV's) and if you want the power the ralley cars made, they go to 10/9.0mm for road and 11/10mm for competition.
Lancia Delta O.E & Performance Parts There are cams available for the QV that do not require piston mods, but anything more will need it. I did close to your Hp with the 145 at 0.75/0.8 bar boost, because the valves open to 9.5mm, low pressure get the same volume of air into the engine.
You will need a larger exhaust above 300hp.
This is not for faint-hearted software tuners anymore.