There's no replacement for displacement

A staple motto of the American muscle car crowd. It means that engine size (displacement) is the ultimate horsepower producing factor of a car, and that other horsepower-increasing devices, such as turbochargers can never fully substitute.

This motto has sound basis. An engine with a small displacement can be modified by car manufacturers to have a relatively large horsepower in several ways, the most important being cam modifications.

Cam modifications shift the torque curve in a certain direction; in this case, toward the high-end range. Since power is proportional to torque times speed, torque produced at a higher RPM level will yield more power. This type of cam modification is used religiously on Japanese cars, allowing cars like the Toyota Celica to get 150+ horsepower out of a Geo Metro sized engine. However, there is a catch. This type of cam modification means the engine will only start making sufficient torque and horsepower at very high RPM's. For example, the Celica makes peak torque at around 6,000 RPM and peak power at around 7,500 RPM. Torque is the turning force that allows cars to accelerate. The more torque, the faster the car accelerates. To have to rev up to 6,000 RPM (which is the engine redline of most cars!) just to get sufficient torque for a fast launch would take a long time, and the massive amount of high-pitched noise that is produced at such a high RPM level hinders any pleasurable experience one may have from driving the car.

An engine with a large displacement, however, has enough horsepower being produced by merit of its size that no radical cam modifications are needed. Therefore, there is much more low-end torque, meaning that the torque is readily available at commonly-reached RPM levels. The Chevrolet Camaros of old, with their 300+ cid displacement, had a torque peak around 2500 RPM!

Following on from sideways' writeup about technology triumphing over sheer engine size, there are a couple of other factors to consider. First of all (and this is a pretty obvious one), the age of the engine must be taken into account, although this is essentially another facet of technology moving with the times. My 1975 Toyota Corona has a two-litre engine, but it's not even going to come close to some new plastic shitbox hatchback with a 1.6 or perhaps even a 1.3 litre motor.

Secondly, it is important to consider just what the measuring stick is for judging cars. Top speed? A car's performance can be gathered by measuring it's braking horsepower, which is how much energy is needed to stop the car (or kilowatts (kW), or Newton metres (Nm)). Often though, the best test is acceleration - measured by the time the car takes to reach the speed of sixty miles per hour from a standing start (refered to as 0-60mph (around 100km/h)), or the time it takes to complete a quarter of a mile (the 1/4 mile) from a standing start. Engine displacement is obviously not the only factor that influences the time. Curb weight, aerodynamics, tyres and track conditions all contribute.

So what does it all mean? In other words, unless you're going to put you foot to the floor, (and even then) sheer engine size isn't the only factor that decides performance. As sideways pointed out earlier, there are many replacements for displacement, some of them more effective than the extra cubic inches. In the early 70's in Australia Chrysler Australia released the Charger, a sports car version of the Chrysler Valiant. At it's best model (the E49), the car featured a 265ci Hemi straight six (4.35 litre) which was able to score a 1/4mile in 14.1 seconds, stock: Way better than any 350/351 litre Holden or Ford at the time, and even up to (and possibly after) 1997, was still the fastest Australian production car, even compared to the brand new 5.7 litre V8 Holden GTS-R. New tyres brought down the time to 13.8s. This is comaparable to American big-block V8's, and a tricked up Charger was and is definitely a force to be reckoned with. Not bad for a six cylinder!

To sideways; there is still nothing like the feeling of being behind a big V8, even if it's not the greatest performing car on the road.

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.