Winning the MPG/0-60 tradeoff


A friend of mine just bought a car.  He happily told me it gets amazing gas mileage and accelerates great from a stop.  I smiled and kept my mouth shut; I've seen the car's spec sheet so I know it's not fast, but why spoil his fun?  On the other hand, instead of pitying his misunderstanding, maybe I should envy him for successfully faking himself out:  he got the feeling of acceleration without paying for actual acceleration.

He traded in a giant American V8 sedan with some unholy level of horsepower.  I'd been in that car - driven it, even - and I know he liked the power.  His new car is a VW Passat TDI.  That's also a full-sized sedan, and not a lightweight one, but the TDI engine makes about half the horsepower his last car did.  It gets from zero to 60 about one second faster than a Prius.  So how is it that he's so happy about its acceleration?

Answer:  it's a diesel.  Power is torque times RPM, and diesels tend to have a lot of torque but they can't rev to high RPMs.  So when the light turns green and you step on the gas, a diesel makes a deep HURRRRR sound instead of the higher pitch of a gas engine.  Psychologically, in your head you're expecting that deep tone to go along with lazy acceleration, but the diesel's torque accelerates you better than you expect.  It feels fast.

Car design involves compromises.  Quick cars tend to be thirsty.  My friend values fuel mileage, so he found a way to be happy with the acceleration of a fuel-efficient car:  he's fooling himself.  He probably even knows it, he's got an engineering degree.  But I'm not going to be a jerk and point it out, and risk ruining it for him.  I wouldn't want someone to pull a hipster move like that on me.