Although Shining Arcanine's premise is an interesting one, there are several problematic areas. Fuel economy is not just about engine size and/or aero. It's also a function of weight and tire rolling resistance.

When people decide they want a "luxury car" what are they really saying? Typically they are saying they want a vehicle that is highly refined (quiet and smooth), has a solid, safe feel, quality and durability, has excellent ride and handling characteristics, decent to overwhelming performance and a lot of high tech goodies. So how does all this come together?

Well, as someone has already mentioned, when you put 4 cylinder engines in progressively larger and or heavier cars, they tend to have to work harder and they get noisier (not refined) and hotter and more prone to breakdown (less durable). Since they have to spin at higher rpms, a 4 cylinder in a larger car would be less smooth at highway speeds (again, not something the luxury buyer wants) than the same engine in a lighter car.

So, why not just make the luxury car lighter? Well, there is a lot of work going on in that area, but the requirements for more content (safety equipment like multiple airbags, antilock brake systems, traction control systems, ultrasonic and radar based park assist systems, cameras, alarm systems, you get the picture) add mass. Other than the safety content, you could strip some of that stuff out, but then you wouldn't have a luxury car anymore.

Lastly, tires can not be ignored. There is significant stress in the vehicle development world in striking the right balance between tires that have low rolling resistance (easier to get moving, more difficult to stop), smooth ride (luxury focused) and excellent handling (wide grippy sports car focused tires).

There are a few entry luxury cars that have 4 cylinder engines. BMW 3-series vehicles have had 4 cylinders for years. For US models they are going away from 4 cylinders in favor of Inline 6 engines because the demand for 4 cylinders is low and the performance of the 4 cylinder versions is suffering from all the things I've mentioned above. The Saab 9-5 has a turbo 4 as a base model and it gets pretty decent fuel economy, but it's content is luxury more from a European perspective of luxury than a US perspective.

Someone mentioned that the ability of the Corvette to get decent fuel economy from a 400 hp engine is an indication that 4 cylinders could be made powerful enough to power larger cars. The reality is that the engine in the Corvette is waaay beyond what is required to power the vehicle under normal circumstances, so the engine basically loafs most of the time. The automatic transmission in the Corvette is very efficient and allows the engine to operate in its most efficient ranges. (The same basic transmission is also used in most GM pickups and SUVs.) Most people aren't using anything approaching the 400 hp that's under their right foot. The same vehicle with a 220 hp V8 would probably have less efficient fuel consumption.

Peace,

Martin

I am NOT the official voice of GM with respect to Hybrid issues

I am NOT the official voice of GM with respect to Hybrid issues

I am NOT the official voice of GM with respect to Hybrid issues