pulling apart a motor is easy, any monkey can do that 
Putting it back together, AND use up all the nuts and bolts, have it run Better, smoother and with more power is a different ball game.
Trouble most get into with cars is putting Bigger diameter wheels on… They have a little Jap car, put big dia wheels on to look good and for better handling etc - except the extra rolling weight of the big wheels is too much for the engine - so more power n torque will help bring speed back - but now it can turn corners Faster. Faster corners means better lap times.
The other thing that is proven, is if you want a faster car - buy one already built that way - forger about custom jobs - far more expensive. Much cheaper to buy one already Fast.
Unless of course, you just like tinkering.