the car is h22 turbo.

 

Depends how big the leak is I suppose. Is the Manifold damaged or is it just the gasket. If so fix it right away!

 

In theory, you'll only loose power before full boost, meaning a longer spool time. In the real world, that exhaust gas stays in the engine bay a while. I doubt your intake is sucking in outside air, so you'll have it sucking in that hot inert exhaust gas. Higher IAT's and less oxygen mean less power & a extra-rich mixture.

I know someone claimed 50whp increase in a street turbo setup just by extending the dump tube from under the turbo (straight down) to behind the oil pan.

 

yea because when i got it tune, it make good power until 5.5k rpm and then the hp flatline and we couldent figure out why.