question about my peugeot 306 1.4 ,and l would like to add turbo to my engine , how much more HP the car will have,,and how faster it will be,is it a good idea?

Here is the horsepower on ur 306 engine: 75hp.
1.4 L (1360 cc) TU3 I4, 75 PS (75 hp/55 kW) & 89 ft·lbf (121 N·m) .... (an 8 valve head engine) (top speed 102mph)

And u would like to add turbocharging.
You would have to buy a lot from an aftermarket ''turbo'' company. Then.what would u do about all the electronic changes ur engine would need? Sensors for speed, temperature, pressure, rpms?
Is there enough room in the engine compartment for the turbo & the exhaust collectors?

Please spend the same money, OR LESS, on a 2.0 liter Peugeot 306 & have it all done for you. Look at the horsepower increase u automatically get:

2.0 L (1998 cc) XU10 I4, 123 PS (121 hp/90 kW) & 129 ft·lbf (176 N·m)
2.0 L (1998 cc) XU10 I4, 135 PS (133 hp/99 kW) & 137 ft·lbf (187 N·m)
2.0 L (1998 cc) XU10 I4, 150 PS (147 hp/110 kW) & 135 ft·lbf (183 N·m)
2.0 L (1998 cc) XU10 I4, 167 PS (167 hp/124 kW) & 147 ft·lbf (200 N·m)
these 4 engines include 8 or 16 valve heads, double overhead camshafts,..(top speed 125mph, 6speed gearbox = 135mph)
In fact, here is a website of EVERY 306 engine & model, & the horse power, top speed, 5/6 gears (gti-6 had 6 speeds). Find a new car here:
http://parkers.co.uk/cars/specs/Summary.aspx?model=650