To be honest, you're wasting your time (and money) chasing numbers.
As you're attempting NA tune without opening the block, I assume there is a budgetary consideration.
So cheap stuff is induction (ram scoop at a high pressure area at the front, tweaked inlet piping for best flow, really really good exhaust system, uprated ignition system (better plugs, larger, individual coil packs) and a piggy back ECU are the 'easy' stuff, each of which is going to cost you plenty. Coupled with some wild cams, and a very high rev limit, this will either see you with a 200bhp NA car that is horrid to drive or a rod through the block.
The unfortunate thing with NA tune is that you pretty much HAVE to open the block: to get lots of power you really need to rev, which means carefully balanced rotating mass, and to get the air in at the right speed you pretty much HAVE To port the head, as it's optimised for low end torque and driveability.
You can get bigger numbers, but compromises have to be made.
Honda typically rely on Hand finished heads, extremely light and carefully balanced rotating mass, and approace (or exceed) the magical 100bhp/litre threshold. But in doing so, they sacrifice some of the driveability: There is nothing worse than being caught in the wrong gear in a Honda: it's gutless. Or try going 4-up, or carrying something heavy: there torque figures are so small that the blistering performance is severely muted, and you can feel it.
Homda use VTEC to alter the cam profile for a specific rev range: this attempts to retain some low end torque and driveability, as well as refinement, but keeping the exhaust valves closed longer to build torque and reduce noise. Without this, the car would drone on and feel awful below the "on cam" range (usually 4000rpms and above).
Your best bet is to fit an exhaust and airfilter to start with, and see how it does.
Careful selection of oil is vital. Uprated plugs and coils will help.
This is all the cheaper stuff, though a properly designed exhaust is going to be expensive: it will need to be computer modelled by an engineer specialising in the field.
Then drive it and see if you're happy. At this point you can decide if it's worth investing in a piggy-back (probably) and cams (probably not, as they will be pricey).
A better idea would be to put the car on a diet: start removing heavy things you just don't need.
AA membership is a lot lighter than the spare wheel.
A smaller battery will save a lot of weight.
ABS...do you want it? It's pretty heavy.
Windows can be changed for plastic.
Panels can be changed for carbon fibre (try lifting the bonnet with one finger! )
Boot carpets...
Speakers....
Subwoofer...?
Removing weight will have a much bigger impact on the cars handling and point-to-point performance than an extra 50bhp.