Turbocharging is a great way to make your engine produce more power but it is not as simple as just bolting on new manifolds and a turbo.
The purpose of adding a turbo is to force feed as much air as possible into the cylinder which means you can burn more fuel and therefore produce more horsepower. A naturally aspirated (NA) engine can only suck in a certain amount of air before the inlet valve closes, sealing the cylinder and preparing for compression. This is generally only around 60% of the cylinder volume. Even using the latest and best tuning techniques, the best you can hope to do is increase this to around 80%. Adding a turbo can increase this volumetric efficiency to around 120-150%.
Running higher amounts of boost means you can effectively have a small turbocharged 1.6 engine producing more power than a lazy big V8.
One thing to be aware of is that as you add more air and fuel, you are also effectively increasing the compression ratio. Too much compression and your engine will go bang. In order to reduce the chances of this happening, pre-boost compression must be lowered. An issue of high compression is pre-detonation, also known as pinking. This happens when the air/fuel mix has been compressed so much that it ignites on its own without a spark from the spark plugs and before the piston has finished the compression stroke. This explosion of the air/fuel mix effectively tries to push the piston in the opposite direction from which it is travelling. If you’re lucky, you will only end up with small pits and marks on the piston crown and cylinder head. If you’re unlucky, you can end up with broken connecting rods and a hole in your engine block. There are a few ways to reduce the chances of detonation such as using water/methanol injection and higher octane fuel but if you’re planning to run high levels of boost, you must reduce pre-boost compression. This can be achieved in different ways such as a rebore with wider pistons, use specially designed low compression pistons, fitting a stroker kit, using a thicker head gasket (I have also seen some people building engines using 2 head gaskets).
Direct injection technology as originally used on diesel engines has now found its way onto petrol engines. Fuel is injected later into the mix than before. This lowers temperatures and helps to deal with the pre-detonation problem.
When adding a turbo, you will have a lot more gases flowing through your engine so it will also help to do some work to the cylinder head to maximize gas flow. Polished ports, larger valves, larger exhaust manifold will all help.
Fitting of an adjustable boost controller will help you fine tune optimum pressure and timing advance.
Now that you have more air flowing into your engine, you need to pay attention to fuelling. If you don’t have enough fuel in the mix and the engine is running lean, it will be running a lot hotter than before which can result in melted pistons. This can best be managed by using an aftermarket ECU which has been specially designed for turbocharged applications. An aftermarket ECU also means a new wiring loom and new sensors so don’t forget to budget for this as well.
Before you even think about turbocharging your engine, you should research and read as much as possible about your particular engine, see what other people have done before you. Make sure your engine has a good strong block. Not every engine will be strong enough for turbocharging. There are a lot of bolt-on turbo kits on the market for a lot of cars but don’t forget, it’s not as simple as just buying the parts and bolting them on and you’re finished.
**DISCLAIMER** I accept no liability for any harm or damage caused by anyone modifying their car. Always read the workshop manual for your car and consult a qualified mechanic before starting any work.