Ok, because I cant see it above.
Basics, valves open and shut to let the fuel and air in, and exhaust gases out. Has to be timed so the piston pulls in the air, and later pushes the exhaust gases out.
More performance means you want the valves open more (time and travel), and also higher compression (small the combustion chamber is).
Older engines are lower performance, and the valves generally dont open far enough to touch the pistons. Higher performance engines do have that risk, and it's a no brainer as the valves are very fragile compared to a piston and will get broken on contact.
More advanced engines by varying the valve timing or duration. There's a whole area of tuning to do with optimising the gas flow, the timing can be tuned to the revs and accelerator (air flow).
Simpler engines have a fix cam timing, locked to the crank timing.
VVT is Variable Valve Timing, ie it changes the cam timing depending on engine speed and load. Different makes have different methods of changing the timing. The funny large mass in the pulley allows the camshaft to change it's phase or angle to the pulley.
The fiat system is clearly dodgy as they took away the timing marks, meaning they think it needs manually set each time. Personally I cant see why they cant have conventional timing marks to line up.
Oh my, you're a brave man to try taking this subject on in such a small space! Well done.
I'm not brave enough to even try but it's interesting, perhaps? to consider that the more fuel/air mixture you can get into the combustion chamber the bigger the "bang" is going to be when it's ignited. Lots of things conspire to limit this, the design of the inlet manifold and porting. How restrictive the valve is to airflow (the longer you can keep it open and the further it opens is better, which is what camshaft design and VVT attempts to improve) but perhaps one of the biggest problems is that, even with a perfect design, where the piston going down in the cylinder would create a "perfect" vacuum - which in the real world it can never do - the maximum "pressure" acting to push the air through the inlet and into the cylinder is atmospheric pressure ( generally accepted as 14.7 lbs/sq in at sea level). It's useful to think of this "problem" in this way because no matter how "hard" the piston tries to "suck" the air into the cylinder you can't get more than a 14.7 lbs/sq in pressure differential between the outside of the engine and inside the cylinder which must, no matter what you try to do by way of camshaft and inlet design, be the final limiting factor. This is one, although not the only, reason why turbo charging has become so popular. Stick a turbo, or a less popular supercharger, on the end of the inlet and immediately you can increase the pressure of the air being fed to the engine and, everything else being equal, you'll end up with a lot more air in the combustion chamber so you can "squirt" more fuel in (because with more air you can burn more fuel) and therefor you get a much bigger bang and more power! Of course in practice, it's not that simple but the general principle of cramming more air in is easy to understand.
The manufacturers have taken advantage of this to be able to fit smaller engines to their cars thus getting better economy when driven gently but, with the turbo, still giving the vehicle a decent ability to pick up it's heels and go when needed. The down side is that if you use the performance most of the time you'll get pretty poor fuel consumption. Change up early and use small throttle openings and you can get surprisingly good figures - have you noticed how most of these vehicles have a "recommended gear" indicator on the instrument cluster which seems to be always encouraging you to change up to a higher gear? Seems to me to be the manufacturers trying to negate the "fuel guzzling" propensity of these engines?
I do think it's a little unfair of you to classify the FIAT system as being "dodgy" when most modern engines don't now have timing marks and unkeyed pulleys. My wee EA211 engined Ibiza, and now my new Skoda, have unkeyed pulleys on both cam and crankshafts. My guess would be that they are obsessed with having valve timing absolutely spot on - much as would be with a racing engine - to get best possible power and fuel consumption. Older engine's fuel and ignition systems were less exact so unable to benefit from such exacting valve and ignition timing to say nothing of modern direct injection fuel delivery. However, whether the wee F.I.R.E. engine with it's relatively simple port injection and, even with VVT, quite basic valve actuation, is highly debatable. I've done belts on them using the recommended tools and loosening of the cam bolt (only did it once this way) and by the "tippex" method (with the qualifier that I always check valve timing, using the tools, on an engine I don't have previous knowledge of) and I can't detect any difference in how they drive afterwards.
big wheel on the cam shaft little wheel on the crank.
