Installing a twin turbo is like a $4,000-$10,000 job. There is no cheaper way to do it.
Watch these guys install a turbo and understand that even them: with a FULL shop with lifts, degrees from automotive training institutes, and a flow of money from their show, along with 8 or so guys to help STILL struggled to put in turbos.
It is not a one man job, for a person with little experience. It is something that you need thousands to do and experience to get done properly.
I wish it were easier my friend, but there is a reason it is so hard to get more horsepower.
There are other ways to grab 20-40 horsepower here and there, porting and polishing the engine block, etc. But are you comfortable opening the block and do you have the tools and expertise to port and polish properly?
Adding horsepower is not easy. But everyone has to start somewhere.
Just keep in mind this is not something you can do for hundreds. Its going to be thousands of dollars to be adding real horsepower.
If you lack experience, add much more to that number because mistakes in this area will be expensive, when parts get broken or damaged or mis-installed, the results can be catastrophic. Eg. Can you imagine installing new engine block or rebuilding after it is blown?
So yes, you can add horsepower, but this is not a cheap hobby unfortunately.
So yes, if you wanted the easiest, cheapest way to do it, you should have bought the higher horsepower vehicle in the beginning, that came that way from the factory. That is the cheapest, easiest, most direct way.
I know its hard to hear, but its the truth.
Watch the donut media video and see exactly what Im talking about. This stuff is no easy task.
There are unfortunately no easy, cheap shortcuts to 100 horsepower gains.
Though everyone has to start somewhere. If you are determined, start reading books by James Halderman about engines and getting to know how they work.
Start watching turbo install videos on YouTube.
And start saving up, because even a single turbo kit for a BMW 118D is going to cost you about $2000 plus shipping minimum
This kit is capable of ~290-300bhp with 350-400lbs of Torque (with supporting mods) and will out perform any hybrid stock turbocharger
www.google.com
And that does not include all the tools you may need to invest in, including likely an engine hoist and engine stand (in the U.S. you can actually grab both from harbor freight for likely under $500) among many others.
But the knowledge is important. If you fire this entire setup up for the first time and it blows, you are now burned on like $2000 minimum + engine itself potentially, and a new engine for a low end BMW is like $12,000 from BMW
2008-2013 BMW Engine 11-00-0-421-180
www.bmwpartsdirect.com
Unless you are going salvage for a new engine, which is a total crapshoot. Would not ever go for a salvage engine unless you plan on totally refabbing/refurbishing/rebuilding it.
So these are all things to consider. Yeah man, its gonna be expensive. Can you do it? With enough money, knowledge found/gained, and perseverance and inspiration, you sure can, but you are going to need money, space (an empty garage a larger one preferably to pull an engine) to do so and get ready for setbacks.
You would not get something done like that in a week alone. Donut media barely got it done in a week, working all day (its their day job) with lifts and multiple guys and expertise to some degree.
Be ready to be working on your car for like a month, or two or more, because unforseen things like part shortages from BMW, (when you break a small part accidentally, etc) will definitely hold you back.
Good luck my friend. I hope you can see what you are getting yourself into.
Anything is possible but you must be realistic.