Why wouldn’t a faster engine speed give more power?
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Engines are designed to work best at certain RPM ranges. The main factor that affects this is the profile of the cams and the design of the valves. In a perfect world every exhaust stroke would expel 100% of the exhaust gasses inside each cylinder; if this were the case, the amount of power the engine produced would be directly proportional to RPM, i.e. if an engine made 300HP at 6000 RPMs, it would make 150HP at 3000 RPMs; it doesn’t work that way. When gasses leave the cylinders they leave in 3 separate pulses.
1. When the exhaust valve opens the higher cylinder pressure forces the gas to rush out into the exhaust manifold
2. The majority of the exhaust gasses leave as the cylinder rises during the exhaust stroke
3. The intake valve opens up slightly before the exhaust stroke finishes and the exhaust valve remains open during part of the intake stroke. The inertia from the gasses inside the exhaust pipes draws the remaining gasses inside the cylinder and fresh air fuel mix is drawn in. This is very bad for low end performance because the gasses aren’t flowing fast enough for this to have a positive effect. That’s why muscle cars have that classic rumble at low RPMs.
Modern cars have a trick called variable valve timing that allows them to adjust when the intake and exhaust valves open in relation to each other depending on engine speed and load. At low RPMs there is very little overlap and at high RPM and high engine load the intake and exhaust valves have much more overlap.
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