There is no single answer for this question.How many horsepower & how fast any given car will go depends on the unique individual setup, engine tuning, road/weather conditions, transmission setup and of course, the driver’s skill.
Generally ,turbo manufacturers do provide warranty for OEM market ( those fitted in new vehicle) , but they DO NOT provided warranty for aftermarket use.
Please read through the letter by manufacturers.
A properly assembled and balanced turbo requires no specific break-in procedure. However, for new installations a close inspection is recommended to insure proper installation and function. Common problems are generally associated with leaks (oil, water, inlet or exhaust).
Not necessary, a turbocharger horsepower is rated by its ability to compress in and exhaust out that much of air volume to make their horsepower rate. Anyway, your engine must be able take this amount of air in order to generate that horsepower rate.
Anytime you install a turbo on a naturally aspirated vehicle, or upgrade the stock turbo(s), it’s important to upgrade the supporting factions of your car’s fueling system. What needs upgrading will vary greatly from car to car; anything from injectors, to fuel pumps, or engine management. The determining factor will be the goals for your car.
Depends on the goals you have for your car, as well as other factors such as engine strength and engine displacement. Additionally using an extremely large turbo on a small displacement engine, will make for a very short, unusable powerband.
Many things can be done to increase your turbo’s power and efficiency. The turbo housing can be milled out, different diameter wheels can be added to increase horsepower, the wheel can be clipped to different, varying degrees to increase horsepower and response time.
http://www.turbobygarrett.com/turbobygarrett/tech_center/faqs.html#turbo
Typically a steady state dyno(Example : DynoDynamic) will give results of up to about 20% less than inertia types(Example : Dynojet). This is due to they are using different way to meansure the figure. Eventhough a same dyno may give different result due to the dyno was not correctly calibrated, the atmosphere (Weather) conditions had changed or the vehicle had a problem that affected its Power output.