as above 350 is the magic number with a Scooby enough to be a very fast car but still low enough not to be too hard on the rest of the drive train,to do it right you will need to drop it to ali burrows,sti tuning or any good builder for a rebuild with pistons ,bearings,gaskets,oil pump etc then fit a tdo5-20g turbo and sti 550cc injectors and top mount or front mount full decat exhaust and a remap .at that you will have a reliable 350 no hassle.if budget is an issue just full decat ,vf35 or vf48, injectors and a map you should see 300 bhp