The main reason for looking for more power is that I'm not confident the current engine is going to last. When I start the car on a morning first thing, it stumbles and nearly immediately cuts out. It'll restart again fine but the idle control valve is defo faulty. Whether it would cause the other issue I don't know tbh but mpg is only 25 at best and there are also turbo worries. It has leaky turbo seals and there is blue smoke from the exhaust when warming up. It was only rebuilt 30000miles ago and same time period the car had new pistons done. But the turbo was rebuilt with 360deg bearings and was race spec balanced. How would these turbo mods affect drivability if nothing was done map-wise? The car had horrible emissions on the MOT machine makig me think all is far from well with it. Would I be best getting a used zetec block and getting turbo rebuilt and converting that or could I use a ST170 bottom end and 4-2-1 exhaust manifold with current inlet and head and mapped accordingly?

Comments please as I love the car but really just wanna make sure it's 100% reliable.