I took my twin-turbo FFR to the dyno a month ago to have a chip burned. With only 9 lbs boost she made 454 HP and 488 torque at the rear wheels, with STOCK heads. Ended up putting a set of Brodix aluminum heads on since then to help with the breathing. Haven't been back to the dyno but I feel certain the heads added 30-50 hp.
Feels really, really strong. It ran low 12s before the turbos, on drag radials, so I feel confident it will go low 10s, maybe even high 9s with the "twins".
I will post after I get to the track.
Later,
Mike