set of headers and a dual 2.5" exhaust with some flowmaster mufflers and a edelbrock 4bbl. intake with a 600CFM 4 bbl. carb.
a better way is to change out the 8-1 pistons for a higher compresion ratio 9-1 10-1 11-1 12-1 ect call ross racing pistons they got em or wiseco
best way to pull an engine 318 bmw
Start with a cold air intake, then add headers. If you want 100 or more horsepower instantly add nitrous
Only you can determine what is best.
Easiest/cheapest way for a few more horses are an upgraded performance carb/intake (Holley/K&N, etc) and a less restrictive exhaust (high performance muffler, etc). Then they start to get more expensive - superchargers/turbos, etc.
There is no easy way to increase horsepower but probably the easiest way is to add a nitros system. Be aware that you can destroy the engine with nitros used incorrectly.
Forced induction.
The cheapest way is to use Nitrous but research it before going this route.
hook a horse to it or buy a 350
get an electric radiator fan anf take the blades of the belt driven one 10-20 more horsepower
If it is a gas or diesel vehicle performance tuners are the cheapest reliable power and they are unreal.
The fastest and easiest way would be to install a tuner but of course there are many ways to get more horsepower like an upgraded turbo, intercooler, cold air intake, injectors, etc.
Install a computer chip upgrade to improve fuel injection and ignition output. This is the most "efficient" way to add 50 horsepower. The quick and dirty way to add more horsepower is nitrous oxide. Putting the motor on a single-stage NOS bottle will raise horsepower, but threaten the viability of the engine.