Nandishpal,
I can help you out with your Subaru Forester. You can swap a turbo on to the 2.0 Forester engine because it's basically the same engine that is in my WRX. We can apply a few tricks from my blog at
Subaru Off Road where I databased almost everything I've done to my WRX. Before you do any modifications, get a wideband air to fuel ratio gauge to monitor rich and lean conditions. EGT gauge also helps detect damage.
Let's start with the biggest restriction:
TGV Deletes - This is a huge restriction, it's a butterfly valve and actuator that sits inbetween your intake manifold and the intake head. Some JDM models do not have TGV's, this may not apply to your forester. To check if you have TGV valves, you can look and see if your intake manifold goes completely to the head or if there is a separate unit inbetween the intake manifold and head. If there is a separate unit, you have TGV's and they should be removed. While removing the TGV valves, add some phenolic gasket material in between the bottom of your TGV and the head. This 3mm or 7mm spacer material resist heat up to 300F. This will cool down your intake charge which helps make power.
Start removing other restrictive parts like emissions equipment. The stock headers are fine but you need to take off catalytic converters, baffles, and stock mufflers. These are all very restrictive. Next, change the intake to cold air with cone. A good cone in your fender is better than hot air from the engine bay, or using the restrictive stock intake.
You'll need to retune your ECU for these changes, and that can be done with a laptop and tactrix cable. Get some free tuning software like OpenECU. Make sure you have plenty of fuel to air, and then try adjusting the timing. Do a little bit at a time until it's perfect. Or you can download premade maps. Either way, you'll need to retune the car if you've got modifications. You can do all of these mods with out a tune and risk running the car too lean. Just keep an eye on mods as you do them and if it starts to run lean then you know you'll need a tune. Basically, let the engine breath better and consume more fuel and you'll make more power.
You can add a turbo to your engine and make anywhere from 250-600 hp depending on turbo size further upgrades. Anything past 300 hp and you'll need to rebuild the internals of your engine. Stock internals can handle 300 hp for a while, but break down eventually. If you upgrade to a turbo, get a fuel injectors and high pressure fuel pump as well. The stock rails and lines are fine.
Depending on how much you want to modify, just start with small things. I suggest you read through my blog and adapt what modifications I've done to your vehicle. The engines are almost identical. I hope this helps