Well that 0-60 in 7.7 was without nitrous last summer. Youd have noticed that all these cars that supposedly do sub 8 seconds look pretty shabby when the results are there in black and white. The only quicker cars on the day were 106 gtis or 2.0s or turbos. So I was pretty pleased with that.
Dont know much about dry systems, but they seem to be a bit of a weird way to do things. However it works (and i think I can figure ot from what youve said about the pressure regulator), the bottom line is you must be forcing the injectors to flow at a rate far in excess of what theyve designed for. And if theyre not flowing that much, then youre not getting enough fuel into the cylinders to match the nitrous.
Dry systems seem to be a bit of a wacko idea to me. Mines a wet system with a combined nitrous and fuel injector that fires both in the correct proportion so the ECU has the relatively simple, and safe, task of making small adjustments to the injector duration to keep the mix spot on. Mine was about £600 all up. You could ask what exactly is contained in the kit thats for sale, then get hold of a combined nitrous/fuel injector and get it hooked up to the dry kit.
Your RT would fly with 50bhp, just make sure you dont fire it until your engine is making max power anyway, otherwise youll kill your clutch and gearbox straight away, too much transmission shock. Probably knacker the con rods and crankshaft as well.