I was wondering if my 94' Impreza will fit a bigger motor in it. Right now it has a ej18, AWD. I bought this because its my dream car and i want to boost it up. Please help. Thanks

You can install any engine you want, but if you have to ask this general of a question then you probably don't have the skill set or finances to come even remotely close. 

 

You need to be more specific - who's doing the work, how much cash on hand do you have, what are your skillsets, and what does "boost it up" mean?

 

The easiest power upgrade which requires almost nothing custom or special and tons of people have done it - is to install an EJ25 block under that EJ18 intake wiring harness.  That's the cheapest route but you're still stuck NA and pointless gains if you're trying to modify it any further.  If by "boost" you mean turbo and supercharger - then this isn't a good route.

 

If you want forced induction - turbo/supercharger - then you need a truck load of money or skills for custom fueling, wiring, splicing, and more....and of course expensive parts.  Which usually isn't in the cards for most people behind a post like this. 

 

or you can try to cobble up a home made low boost turbo charger and probably blow your engine up, upgrade to an EJ22, wash-rinse-repeat.