The entire engine will need a rebuild, this will be expensive as most components will need replacement.

New pistons will be needed to lower the compression, these will need new connecting rods, uprated to cope with the additional power. New big end and mains bearings will be needed, so a crank regring will be necessary, this assumes the original crankshaft is strong enough in the first place, if not it will need tuftriding to strengthen it.

A new head gasket will be needed, an uprated item again, to ensure it is strong enough to cope with the additional compression pressures, and heat.

Heat is another big problem as the additional power output means an entire uprated cooling system, this usually means an uprated radiator and piping. Along with this you will need an oil cooler fitting, not the type which is a simple pipe inserted into the radiator, but a new cooling radiator. This needs an additional thermostat fitting to ensure the oil only goes to the oil cooling radiator when the oil gets too hot.

Depending on whether the car is carburettored or fuel injected, these need setting up and tuning on a rolling road. Carbs can be rebuilt and rejetted and set up for the turbo conversion, but fuel injection will need a unique mapping, this means considerable time on a rolling road at around £80 per hour.

Add into this the additional work of replacing additional components such as uprated clutches, stronger engine mountings, and all the other components required, and we have not yet got out of the engine bay. This all adds up to considerable expense, its cheaper to buy a new car.