Again, a common question that I get asked about what should be done and what shouldn’t etc so I will aim to do these for each significant model type.
Firstly, a 2.0 litre WRX….
In std form they are 220bhp give or take and have boost at about 0.95 bar. The boost profile in the std map is pretty tame and doesnt come in til 3500rpm assuming the car is std.
1. Keep the car std but just remap for more oomph and better fuel economy.
A full custom remap will bring boost in much earlier and hold higher boost levels for longer but the map will be geared to running much more efficiently (which is also more economically) as it wont be possible to push too much boost with all 3 cats in place. Typically a Green/K&N/Cosworth air filter and a backbox are fitted at this stage.
This would get the car to about 260bhp
2. Sports cat in downpipe – remove centre cat
A full custom remap will bring boost in much earlier due to the lower back pressure and hold much higher boost levels. The remap will also aim to get it running much more efficiently ( which is also more economically).
Typically a Green/K&N/Cosworth air filter and probably a 3 port solenoid are fitted at this stage (on top of the sports cat downpipe and exhaust system).
This would get the car to about 280bhp but a huge boost in torque figures in the mid range.
3. Fully Decat Exhaust
The low back pressure from removing all the cats is now the equivalent of the turbo running around the garden naked shouting “look at me I’m free”. A remap is needed to bring it under control and stop overboosting. The remap will bring boost in as smooth as possible and most likely get full boost at around 2700 rpm and hold higher boost right through the rev range. The remap will also aim to get it running much more efficiently ( which is also more economically).
Typically a Green/K&N/Cosworth air filter and probably a 3 port solenoid are fitted at this stage (on top of the decat downpipe and exhaust system).
This would get the car to about 280-290bhp but a huge boost in torque figures in the mid range and transform the way the car drives on the road.
A walbro 255 fuel pump is advisable now due to the age of the vehicles.
4. Getting to over 300bhp
A lot of people want to do this, it is a nice bhp figure for the pub afterall. So .. how ? The std TD04 turbo will not do it generally unless you are on a dyno that reads very optimistically although I have seen it several times over the years now. It will need a turbo off its bigger brother STi version.
There are many many choices of turbo for this VF30, VF34, VF35, VF43, VF48, TD05 16G etc etc but all of these will need a couple of other changes to the car before hitting the mark safely.
– STi Injectors – 550cc (Pinks)
– Walbro 255 pump
– worth changing the uppipe for a decat version
– probably an STi TMIC although the WRX will suffice to get just over the 300 mark.
It is also advisable to change to NGK PFR7B spark plugs.
There is a lot of info around about the different turbos and what they are capable of – the VF35 makes the best upgrade in my opinion at the moment and should hit a nice safe 320-330bhp. This is pretty much an ideal level for the WRX keeping it within the capabilities of the engine, gearbox and clutch.
Some other info:
– a vent to atmosphere dump valve will not improve the performance but if you must fit one for the sound then stick to a good make – forge have always been good from what I have seen. (Baileys are less so)
– a FMIC is not needed at this stage.
– an induction kit will most likely not improve performance as the std airbox is very good. If you do want more induction noise then go for a cold air induction kit such as the K&N typhoon where the filter is located away from engine bay heat.
Anyway … hope that is useful.