I'm with rockhopper on this.
If you really want to learn how to tune you really should buy a book on it. That money you'd spend on a chip would be better spent on that book to help you understand how you can tune.
The basic principles boil down to the fact that in order of an Internal combustion engine (petrol) to develop more power you need to get the maximum amount of air in and out of the engine.
The more air you get in. The more fuel in the right mix you can burn. The more power the engine makes.
Engines are very much a compromise also.
Look at the TS block. They are the same block through the range. Same Bore size. The only difference is the crank throw.
The 1.6 Shortest crank. 1600cc 120hp
1.8 Medium crank or square crank 1800cc 140hp
2.0 Longest crank 2000cc 150hp
They all rev to the same amount 6800rpm. So why does the 2.0 not make 160hp?
This is because the trade off in this engine is more torque instead
Imagine a longer crank on a bicycle. Its easier to go up a hill if the crank is longer. But I bet you can't make your legs go round as fast as say a shorter crank.
This is the difference in the 1.6 and 2.0L
The 1.6 has a small crank. It therefore can spin very quickly. This makes the engine faster. More responsiveness.
But equally it doesn't have the torque.
The 2.0L is the slowest spinning engine or response. Because it needs to rotate that heavy long crank.
But the trade off is more torque.
Also if the 1.6 could rev to 10'000 rpm. It would make the same Horse power as the 2.0L at say 7000rpm.
So to tune a petrol. Its always a compromise.
To make more power you need more air and thus the correct amount of fuel. Not over fueling. It doesn't make any more power.
To get more air into the engine. at atmospheric pressure the only way to do that (Without a turbo) is...
Make the engine bigger (Increase displacement)
Make the Engine Rev faster (More rpm = more air = more power)
There are many, many other variables that compromise design and power.
Alfa could easily make my little 1.6 have 200hp. But it would need to rev to 15'000rpm. Have larger valves, shorter crank but larger bore (So valves could be larger) change the hydraulic tappets to mechanical. Then it would have a super hot cam.
But this compromise would mean on paper the engine makes alot of power. But will be pants for doing the school run in.
Companies spend alot on R&D getting the best compromise for the people that are buying the car.
For example. My 1.6 Alfa vs a Golf 1.6.
The alfa makes more power top end. Because the buyer will want to use the rev's have a more sporty feel.
The golf will have a more subtle power delivery but make less power on the specs sheet.
Doesn't mean its worse. It just means its different.
Alfa 166 2.0 Twinnie - LPG and a few trick performance parts