There is so much wrong to this and miss information. First Carburetors make MORE power than fuel injection. Seems wrong but it’s not, that’s why a lot of your big power stuff uses them. Fuel injection is preferred because it doesn’t have to be adjusted as it adjusts itself and can give better fuel mileage. It’s much more convenient, but if youre looking for max power? Carbs are still king.

Not all cars run overhead cams and many of your big power vehicles dont. Look at your supercharged LS’s in your C7 ZR1 or your Dodge Demon with its Supercharged V8, bother run a single cam in the middle and make more power than people know what to do with. Having multiple overhead cams isn’t a necessity and it’s generally not even a major advantage. VVT doesn’t help for Max power and many vehicles with a single mid block cam still have it. VVT allows vehicles to adjust their cam profile to give more low end power. So rather than have a cam that makes big power from 4,000-6,500rpms they can adjust the valve timing to extend that range from 2,500-6,500 without losing maximum power.

Compression is something we’ve always had (and compression was actually pretty high in the past) and how fast an engine can spin has little to do with anything as they don’t really spin engines much faster than previously.

It all boils down to your last paragraph which is like half right honestly. So I’ll give the actual explanation down below.

Cars from the 60’s and 70’s weren’t low on power. In 1968 Chevy released the Corvette ZR1 with an L88 engine that made over 550 horsepower with 610ftlb of torque and 12.5:1 compression. A fucking monster even by today’s standards. So no power and compression was certainly not the problem. Now not all of the engines of that time were so powerful most of them were in the 300-400hp range (for performance engines) but that’s not the full story. They had lower horsepower but much more torque. Back then it was about having that low end grunt that got you moving (torque) much rather than horsepower which is what’s helpful going 150+mph. They had different goals and we don’t see vehicles today naturally aspirated that come anywhere close to those levels of torque.

So what happened? Why did we see the power levels fall from the muscle car era? The first thing people point to is emissions, and sure that played a huge part. Smog was at record levels in the 70’s and they needed to bring it down, so they cracked down on emissions. Naturally emissions control makes vehicles have less power. There was also a second aspect which isn’t as often talked about, and that’s the gasoline. Back then they ran leaded gasoline which is not a thing anymore. Lead in gasoline raises the octane by a LOT. You can still get it but it’s for off road use only because of the health risks. The thing though is cars now have to survive on unleaded 91 octane instead of like back then when it had lead in it and was basically race gas. If you modify a vehicle today (especially a turbo car) to accept leaded gasoline, you can see improvements of a hundred horsepower easily on a stock vehicle. In my race car I get 600+ horsepower switching from 91 to C16 (116 octane leaded fuel).

Between those 2 things that how we ended up with vehicles like the Mustang that went from a 428 cubic inch cobra jet engine making insane amounts of power to a 4 cylinder in the 80’s. The one thing that came out of this was vehicle weight, in order to reduce emissions cars became lighter which was the muscle cars of the 60’s and 70’s biggest downfall. Lighter cars are faster. In addition to that after a lot of technology manufacturers have increased the flow rate of cylinder heads which give more air for more power. Look at a set of stock LS3 cylinder heads and they will outflow modified big block heads right out of the box. On top of that it’s cam profiles, balancing, and finding ways to increase compression back to the glory days without detonation due to the lower quality fuel. Still to this day though those old engine designs from the 60’s mixed with the learnings over the years are still the most powerful engines. A modern engine can’t even come close to the power output of a old big block Chevy when modified.

So in short fuel quality and emissions is the downfall of engine power, and engines didn’t have as high of horsepower in the old days because they were designed to give more torque. At the end of the day the old saying still runs true which is “there is no replacement for displacement”. The bigger the engine the more power it can make. Power adders like super chargers and turbos just add artificial displacement. Vehicle manufacturers today strive for high horsepower rather than torque which is why it seems like they make more power, but in reality they don’t. Look at the Honda S2000 for an example 237 horsepower seems nice but only 162 torque compared to that L88 which made 550+ horsepower and 600+ torque. It’s all in what they are building the engine to do. The only thing they have accomplished really is making engines more fuel efficient and not use leaded gasoline.