Completely honest? No horsepower that is worth the money. If any gains are made they will be small and won't be worth the money spent, in my opinion. D-series motors don't respond very well to bolt ons.
It has been said a million times, so here is one more...any real horsepower is only gained on a d-series with a full internal build with or without forced induction. That is it.
D-series motors were built for GAS MILEAGE. Either enjoy that gas mileage or spend a bunch of money building the internals or adding boost. Don't want to do either one of those and want a quick boost of power...swap to a bigger motor.