I recently took my STi 4 to Power Engineering in Uxbridge for an ECU "Phase 1" upgrade and re-map and I thought that the results might be of some interest to those thinking about it!
The car is a 5-door, in beautiful black mica, with around 7000 on the clock, reg. S11 WRX. I previously fitted a ScoobySport back box and a RamAir filter.
The results are impressive. Although the maximum bhp only improved from 293 to 295 (at around 7000rpm and 6500 respectively), at some 3750 rpm it has increased from 195 to 230, and at 5000 rpm from 225 to 265! The torque figures behave in a similar fashion showing an increase, at 5250 rpm, of some 30 lbs/ft and at 4000rpm a massive increase of some 40 lbs/ft topping out (at that rev rate) at just over 300 lbs/ft. As David says, a power increase is promised but they don't actually say whereabouts!
The overall effect is that the car feels significantly faster--especially in an overtaking situation, overtaking in third from about 4000rpm and upwards is almost scary when you realise how quickly this manoevre can be achieved on the road, but the car feels stable and well within its limits. Although this is an relatively expensive upgrade I am more than satisfied that it was money well spent, far superior to the "Superchip"-type of upgrade. Talk to them about it! Every one at PE was extremely helpful and friendly and the company certainly deserves the excellent reputation that it has. (Used notes please David, in a brown envelope).

In reply.

Thank you for your kind comments.

Regarding the power increase. As you have learned max power is not everything (as anyone who has read it would know). It is where the power increase is delivered.

However by far the majority of cars we have converted have given our quoted figures of +30bhp and +40lbs/ft of torque.

I think that with some of the STi cars they are affected by turbo size and restricted by standard downpipes.

Certainly the STi3 gives a better top end power increase because it has a larger flow turbo, but when all is said and done you are happy and the car is significantly quicker.

Just to give you an idea how difficult this business is, if we had lied and toll you the car was now 330bhp would you have believed us? I suspect yes. So this just showes the importance of torque.

The reverse of this theory is the 8v and 16v Golf, do you remember when the 16v Golf came out and everyone said it felt slower but it had 25bhp more, "how come?" people asked.