Which ECU?
 

What is the difference between a Z4 and a Z5 ecu? Will either fit into my MY93 WRX?

z4 will run higher boost on a 93wrx import and raised fuelcut

mine boosted at around 15psi with the 3 port sel

ok thanks. I'll keep an eye out for a z4 then! After reading through many threads that seems like the best option for a reliable power increase. I guess the other alternative is a scoobyecu upgrade though, but I have no idea how to go about that or if it is safe to hike the power up to 280bhp with standard internals.

Depends on how you drive if you drive it hard all the time the car will break no matter what hp you have.
My mate runs a 94 wrx which has 300 to 310bhp (power fc + other mods) and there is no problem with it just make sure the fuelling is correct and the oil gets changed regularly.
If you have any doubts I'm sure you could find a friendly garage that would check the car for any faults before you start increasing the power.
Also get some new brakes the 2 pots are ****e (Iknow as I have a 93wrx as well)

Your car will run either; the Z5 is similar to the Z4 but it has a higher rev limit. The Z4 is more common and itll make an excellent upgrade for the (any of seven!) ECU thats currently fitted.

A Z4 on Optimax with a decat will see you quite close to 280PS.....


Simon