There is no
replacement for displacement. Let me correct myself: there is one: Cubic dollars
. But for everything else, add the cubes.
Displacement rules because in an internal combustion engine produces power by burning fuel and air. The key to gaining more power is simply to add more air and fuel. Because gasoline produces power most efficiently when it is mixed with air at a stochiometric ratio of 16.5 parts of air to one part of fuel, the limiting factor is air. In a normally aspirated engine air is drawn in the engine by the vacuum created during the intake stroke. The larger the engine displacement, the more vacuum produced. It's that simple. More air allows more fuel and more power follows.
One might argue 'what about all that high tech stuff'. Fair enough. When Henry Ford built the famed race car, the 999 he built about a 20 liter engine. It didn't produce half the power of the 2.0liter Zetec in my Ford SVT Focus. Technology does matter, through engine control, fuel metering and breathing. But it isn't fair to compare 1908 with 2002.
Once you have met the minimum standards of engine management met by all modern cars the key issue again returns to breathing, the ability fo flow air in and out of the engine. You can improve beathing by smoothing air flow in and out of the engine, and by inceasing valve area. The second way is to simulate a larger displacement through pushing more smaller cycles through the engine, in essence by out-revving the other engine.
Smoothing air flow in and out of the engine can be done to both 'low tech' overhead valve and the higher tech.overhead cam motors. The key is good exhaust, intake and port design. The supposedly 'low tech' motor in a 2004 Z06 Corvette produces a very reliable 71hp per liter, and impressive total for any streetable engine, and does so with thumping torque at any engine speed. If you spend more money engineering a lower tech, lower production cost solution to perform very well indeed. Yes, a twin cam motor could do better. But it would cost a lot more, and the DOHC cylinder head is very wide. The small block OHV -V-8 is a very compact piece for the power produced.
Let's now look at out-revving the low tech engine. A standard detroit V-8 is good to 6,000 RPM, right now, and many are good to 7,000. Racing variants can be reliable up to about 8,500 RPM. An racing overhed cam engine can go to 14,500 which is significantly more. But there are some caveats. The biggest of which concerns the cost of parts.
As an engine revs higher a factor known as piston speed comes into play. Internal combustion engines have a lot of reciprocating mass. Piston speed is a good measure for how fast the internal, reciprocating bits are moving. The main revving limitation of a 'low tech' overhead valve engine is the lifter/pushrod system which has a lot of reciprocating mass the overhead cam motor avoids. Fair enough. But as you rev higher piston speed becomes a very large factor. In any motor, once you pass 7,000 RPM you start to need special internal parts. The crankshaft on the Honda S2000 is a really slick piece, whose bearing surfaces cannot be touched by human hands, lest they be damaged. These pieces aren't cheap, and once you start putting them in then the old fashioned V-8 starts revving pretty high as well. The overhead cam engine still enjoys an advantage, but you have to rev it stupid high to obtain said benefits. That may not be enough to overcome any displacement disadvantages.
What about supercharging? Vaccuum is more about air being pushed in to the cylinders and at one atmosphere only so much air goes in. Superchargers mechanically force more air in, in effect creating a bigger engine. The supercharger is limited by design. Turbochargers use a waste gate to limit how much boost they can attain. Cars like the Mitsubishi Eclipse can gain big power cheaply simply by reprogramming the waste gate to a higher pressure.
The big, low tech, motor enjoys one big advantage; torque. Big motors produce lots of it, and produce torque practically everwhere. Small motors can produce torque, but in a much narrower rev band. Small motors make their power higher up in the rev band, which makes the torque harder to use. Big motors are easier to drive. They are more flexible.
But to produce really significant gains over the normally aspirated, overhead valve motor, you have to spend a lot of money. Money for more expnsive parts. Money for more advanced assembly techniques. Any modification you can do to a small motor, say Nitrous oxide injection or supercharging, can also be done to a big, low tech motor with equal results. Ask John Hennessey. I've seen on a race track what a couple turbos and some smart modifications can do to Dodge Viper. The fastest, most highly modified, high-tech Civics are nothing more then roadkill. In fact, we try not to let them on track together because the mismatch is so ugly.
All things being equal, the high tech motor does beat the lower tech motor. But all things are never equal. I like small nimble cars, that's what i drive, and what I raced. But the sledgehammer works. Anyone who races uses the largest engine they can.