One great way to easily uprate and improve a turbocharged engine is with the aid of a hybrid turbo. Sometimes it is quite hard to fit a larger turbo to an engine, the most notable reason being the lack of space available. Add to this the complexity of fitting a larger unit into the exhaust manifold and relocating the oil feed and air intake piping. So you can see that there is a lot to recommend getting different turbo internals in a standard turbo housing as this becomes a bolt in upgrade.
Turbos are simple double ended propellers or impellers. The size, angle and shape of these will greatly affect the performance characteristics of the engine. By adjusting the profile of the exhaust impeller you can encourage early spooling or focus instead on producing a wider power band.
Turbo housings can often be flowed, that is smoothed out and opened up a little allowing a greater throughput of air and this also allows the use of larger internals. Common applications include taking a large turbos internals and fitting these to a smaller unit. The smaller turbo is still externally the same as the OEM turbo and can therefore be bolted straight in place.
Another option is that completely custom made internals are fitted to your turbo. Due to the high rotational speeds it is essential that the internal components of a turbo be balanced pushing the job of hybridising outside of the scope of most DIYers.
Look at the engines existing power band and decide where you want the power to come in and how much more power you want. A hybrid turbo specialist can then work out which profiles to use in your turbo.
The trouble is that you can’t usually have it all. Whilst there is a certain degree of improvement available over the standard OEM turbo you need to select where you want the power to be.
A larger power figure will often mean later spooling and more lag and lowering the spool up time will usually be at the expense of top end power.
Variable geometry turbos are great for this reason as they are adjusted depending on engine speed and load. Sadly it adds another layer of complexity to the manufacturers of hybrid turbos.
So work out carefully what your needs are and have a chat with your local Turbo specialist to decide on an appropriate solution.