To my knowledge apart from ECU issues you can just put it in. Everything fits fine.

You can run it on the UK ECU (needs remapped though) - do not connect the intake air temperature sensor that may or may not come with the STi.

I am using a block off an old WRX, crank off a 2.5 Legacy, modified heads off an STi 5 and a UK inlet manifold and sensors. The only fitting issue was because I was using a Phase I block with the starter motor and bell housing differences but they were minor, and you will not have these issues since both engines are Phase II.

[Edited by john banks - 9/7/2003 10:29:00 AM]

I need more speed and have come across a cheap STi 5 engine, ignoring the ECU for the moment, is there anything stopping me putting it in a uk 99 car? Would I need the gearbox, rear diff aswell?

I have an Apexi ECU that should drive it ok, if I fit the STI gearbox do I need an STI rear diff aswell? What are the differences ratio wise between uk and STI boxes and diffs?

you dont need the diff and gearboxes. If you fit the sti front diff, you will need to do the rear too else you will have a 4.44 final drive up front and a 3.9 at the rear.

Other thing to note is that if you convert to 4.44 front and rear, your speedo will over read to the tune of 54/3.9%, so you will need to adjust this or fit the clocks from an sti.

Hmmm can of worms being opened!!! Are the STI diff's different to mine (RB5) And are they woth fitting?
How much stronger is an STI gearbox compared to mine? Am aiming for 350bhp, or should I not buy the gearbox and put a PAR gearset in mine?

Anyone else care to contirbute?

ratios may be different, speak to andy f about that as he seems to know lots on the gear ratio front.

Personally I wouldn't bother. Think the normal sti ratios are near on identical to yours.

The main difference is the final drive. The gears are no stronger, nor are the synchros.

The final drive will make it accelerate harder, and the increased load makes building boost slightly easier lower down.

I have just switched my 22b from 4.44 final drive to 3.9, and am very happy with the ratios.

With an sti engine you will also have the 8k redline, meaning a theoretical stop speed of 200plus mph. ;)

should add that I have a PAR gearset and am more than happy with it.

if you can afford it and anticipate going for more power later on, then go for it, but at the power and torque levels you are considering, the normal one should hold up.

The sti gearbox is nothing special, nor is the UK box, both can be easily replaced, so stick with them. If you blow them up, then fit the lateral performance box.

Remember electrical problems with going from 3.9 to 4.44 they are the biggest spanner int he works, but can be overcome if you know the right people.