We recommend that you choose the smallest turbo capable meeting your power requirements. This will ensure maximum response and support the widest useable power band. There are a number of different turbos fitted to the Impreza range. Ranging from the smallest very responsive Mitsubishi TD04 as fitted to MY 97 onwards UK and Euro cars including pre 96 UK wagons. 
Next there is the range of IHI VF series turbos fitted to 97-00 WRX and all STI 97 onwards
Finally the Mitsubishi TD05 as fitted to most pre 97 UK, Euro and WRX saloons.

The TD04 can be setup to produce very early boost but starts to run inefficient at higher rpm if used at higher boost levels. A hybrid version of the TD04 can bridge the performance gap to the Sti turbos but with less lag.

The STI VF series are capable of good power but some versions are relatively slow to respond. Their efficiency is improved at higher boost levels but thrust bearings and general construction can limit the maximum recommended safe boost level to around 1.4 bar on Sti 3-6
The TD05 is also capable of making good power and will generally remain reliable at a higher boost level than the IHI series.

We supply seven turbos in our range – the four below are are suitable for standard internals. The remaining three are recommended for use only on strengthened engine assemblies.

AFP4H – is based on a TD04 this is available new or fully re-manufactured on an exchange basis. It is fitted with a new high efficiency, high flow rate compressor wheel and compressor housing which is capable of maintaining the fast spool up rate typically associated with the TD04 but with the ability to run higher boost efficiently over a wider rpm band. This turbo has been tested to levels in excess of 320lbft and 320bhp. With full boost still coming in as low as 2500rpm on a 2.0

AFP5-16 - is based on the 90 degree inlet TD05 16G from the 93-96 cars and can also be converted to front entry to suit 97 onward cars. This turbo is very popular on installations aiming for up to 340bhp. It is available as a fully re-manufactured unit or new. This turbo will typically spool up to 1 bar boost by 3000rpm and full boost by 3300rpm.

AFP30H – This turbo is based around a custom sized Garrett GT30R core. It requires dedicated exhaust up pipe, down pipe and a remote wastegate. A complete bolt on package is available. Spool up to 1 bar on this turbo is typically 3600rpm on a 2.0 litre with full boost by 4000rpm.

On a 2.5 litre 1 bar boost is achieved by 3100rpm and full boost by 3500rpm. This turbo is capable of 500bhp and is only available as a new unit.

AFP35H – Is a custom machined Garrett GT 35R this is also available with a ported shroud compressor cover and requires dedicated exhaust up pipe, down pipe and a remote wastegate. A complete bolt on package is available. This turbo can produce up 600bhp.

Spool up on this turbo is very much dependant on the engine build including factors such as compression ratio and camshaft timing.