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V8 is necessary for a luxury car company to consolidate it's "higher class, higher performance" image. People wouldn't think that 3.5RL is the same level as LS430 or 540i because all RL is using is a 3.5L V6 engine, no matter how well this V6 is, it's still a six cylinder engine, not much different from the one using in TL or Accord(at least most people would think that).
People who buy super luxury car wouldn't consider fuel economy as much as the ones who buy Civic. Sure, emission is very important to our environment, but there wouldn't be many $60,000+ luxury sedans on the road anyways, unlike Accord and Civic, a 4.0RL wouldn't hurt our environment that much right?
As far as profit, why the heck Mercedes Benz and BMW and Lexus make V-8 powered sedans if there is no profit? If Honda wants people to recognize Acura or admit that Acura is as good as Lexus, they have to push their models to a higher level. Quietness and comfort and reliability are the basics a luxury car company should provide, and now people are asking for bonus and image - V8 and RWD/AWD, 6 speed automatic transimission, air-suspension, stuff like that. If Acura can make cars that has some of the above-mentioned items(so far none of them exists on any of Honda/Acura brand sedans), they would eventually make enough profits. Plus, they could use the same or slightly modified version of the sedan-used V8 onto it's next generation NSX sport car. Don't tell me a natural aspirated V6 engine would justify a $80,000 plus price anymore.
I don't know much about pickup-truck market, but I know evey year Ford sells its F150 almost twice the sales of Honda Accord. And if the development of pickup truck could promote the development of V-8 engine, why not? hehe just my idea.