Your engine is NA (naturally aspirated) and it sucks air. It has to suck air through the intake as well. The idea is that with a bigger straighter pipe, you suck more air, and get more HP.
Unfortunately, you have got to be severely restricted already (e.g., tons of bugs, dirt, and leaves over your present air filter) or alternatively, you have to have the engine spun up so fast and sucking air so hard that it is restricted by the OEM intake.
If your airfilter is blocked, spend $15.00 and get a new one. As for the second example, your car will only run at max RPM that last moment before you shift. You may see a marginal gain when going flat out, but there is no bloody way you are going to see a 15-20BPH gain. That's over 10% on a 122 engine. And I'm not even sure if the 122 is at the crank or the wheels. Maybe somebody else knows.
Anyway, you are gonna spend big money to get a little gain.
Other places to spend money for very little return: Larger headers, larger exhaust, cat-bypass, etc.
These can all be done, but on a 122hp engine, your gains are not going to be huge.
If you want to really boost power, you need to look at FI (forced induction) such as a turbo or a supercharger. Or, you need to look at more aggressive internals. Cams, pistons, rods, crank, etc.
There are shops around that do this sort of thing. You are going to be looking at $4-6K for a blower system, either TC or SC. On the lower end if a "bolt-on kit" has already been worked out for the car. Higher end if you need somebody to handle mapping and tuning your ECM.
Better Internals are gonna run you around the same, but fewer places will do it since it is more difficult to engineer the total solution. E.g., you require many moving parts internal to the engine versus some off the shelf parts with some custom EMC mapping, injectors, maybe a fuel pump. But again, there are race shops that will do this.
Do one of the above, and then you will get some serious gains out of a fatter exhaust system, headers, and a big fat intake. Any blower kit will have an intake kit already because one end will be on the blower output leading direct to the intake manifold.
Neither will be cheap, but anything can be done. It gets addictive though, and before you know it, you are looking to go bigger, faster, etc.
Also, each is asking for problems ... for example, I just broke the crankshaft on a supercharged engine about a month ago. Now I have a bunch of engine bits in my garage, and I'm looking at an expensive and time-consuming repair.
But if you do it ... HOLY SMOKES IT IS BLOODY FUN!
Okay ... my rant is over. Not sure what started that!
