There would be a huge gain if the combo supported the turbo. The 70 hpq is the most common TSM turbo and has been 150+MPH in a TSM car. So more cam, heads, torque converter and a lot of other items not mentioned could potentially make 150-200hp more than the 6776. I dont know what you mean by street performance. You will lose some drivability going larger but if the boost and tune is the same on the street as at the track engine performance will be the same. If your going to go to a 70 hpq i assume you are building a 9 second combo that will trap at least 135mph.
No, it's getting dynod this Thursday. We will see where it sits. I've been waiting on getting this thing tuned for a very long time. Hadnt had it past 8# until this past Saturday when I switched to a manual TurboNetics controller and ran at 14#. I don't know how well this car is going to drive on the street at mid 20's. It was ice skating at 14. The car is set up more as a ProTouring style of car, not really a track car. I'll more than likely run it this year at least once. We shall see.