I have no experience with a bb turbo but I do have a 70 gtq. I have had little time tuning the car since I put a fast system on it. In Reynolds the car was spitting and popping the entire 2 days I was down there. I was letting off of it before the 1/8 mile marker and was coasting to some 12.50's so I knew the car would put up a good number. I tinkered with it and never figured it out until I got home and found the culprit. BAD COIL PACK !!
Well, to make a short story long, I finally realized it wasn't detanating because the fast was telling me it was extrememly rich. I remember reading like a 9.5:1 air fuel at one time. So for the last run I stayed in it all the way through. It was still bucking and popping, I had a 1.63 60 foot it pulled 2 deg. at the 6 sec. mark, 2 more deg. at the 7 sec. mark and then 10 deg. at the 8 sec. mark.
I netted a 6.71 at half track at 106 mph, and a 10.50 at 122. It really nose dived when it pulled the 10 deg. I have tons of tuning to do, and I havn't even messed with the timing yet. I have ported irons, atr 4bolt headers, fast, 85's, 70mm tb, steel caps with a girdle, oliver rods, steel crank, and the car weighs 3830 lbs with me in it. Next outing should be some high 9's (if nothing else goes wrong) at 27-28 lbs. I was told by precision the gtq makes power up in the low 30lb range, but I'm not gonna push it. I have been very satisfied with the gtq, but like I said, I have never had a bb turbo.
This is my experience with the 70gtq on a heavy azz car, and a not so experienced tunner.