How do you keep a car naturally aspirated and increase power? I don't think there is as much options then other types.

exhaust, cams (this is forza logic, im no expert)

• first of all: weight reduction, bro (you wouldn’t believe how much rear seats weigh)
• an engine is something that breathes (try breathing with a stuffed nose ;-))
• if you get a used car, clean the intake manifold and throttle bodies etc
• get manifolds that are wider,
• camshafts control when your valves open and close, you can fiddle around with that,
• ignition timing - the earlier the better, but not too early, no woman likes that ;-)
• if you want to increase laptimes etc, upgrade the brakes (you can brake later - therefore be faster for a longer time
  (but please consider this: don’t just power up the engine, make it better. there are going to be higher forces and the parts have to deal with them, and nobody likes an engine thats broken)

cams, injectors, valves, bigger pistons/ bore, intakes, exhaust.
classic hot-rodding stuff!

3 words, bore and stroke.
Or bigger cams (lopey cam), bigger intakes, etc.

Changing the camshafts to a more aggressive (i.e. longer duration and higher lift) profile is a good way to make power at the top end, but a common misconception is that they add more torque; they actually move the torque band around. Less aggressive cams will give you plenty of torque practically from idle upwards, but will reduce torque at the top end - sometimes the car will struggle to accelerate in the last few hundred rpm. More aggressive cams will move the torque to higher rpm, and thus increase power (power = torque × rpm ÷ constant, so the same torque at higher speed means more power) but will make the car accelerate worse at lower speeds. Idling speed will also have to be raised to over 1000 or so, because at around say 700rpm, with aggressive cams the engine won’t produce enough torque to idle smoothly.

Well the easiest answer is always on the inside of the inside: cam, heads, pistons, ect. Also, there is no replacement for displacement. However, you cant just mix and max parts. A wrong pair of heads on a cam will kill power and gains, same with all the parts. But lets assume that you dont want to tear into your engine.

First is flow. Better intake and exhaust will increase power because there is more air coming in and its easier for it to go out. And with more air, you want to add more fuel to the mix. In an car with a ECU should compensate for the fuel mix, but you can also upgrade the injectors.

Weight reduction is also a plus, and not just in terms of changing seats. If you get better and lighter pullies, especially on cams, even the smallest weight change on the cam pulley means a huge difference in load. Depending on the engine, you can take tons of load off the cam by changing pullies.

You can also upgrade normal parts in the engine. Better sparks and wires will give you a better spark. Better cooling system will keep things cooler. Better ignition systems and timing will increase power bands. Pretty much better parts will increase power and performance.

New pipe with aluminium with antimony to save the pressure from engine, new camshaft, new modify ecu, new rail pressure, new injection system for more pressure, weight reduction, new intake system and exhaust system, new transmission for more power in wheels