Why (some) GM products suck

[Urbane Guerrilla]

Originally Posted by sugarpop

Yes, gas mileage has actually gone down over the years, instead of up. It's sickening. And on this show I watched recently (Futurecar), they said that only 25% of the fuel is actually used to propell the car. 75% comes out the tailpipe. I was stunned! How extremely inefficient is that, and STUPID? Other forms of fuel don't have that inefficiency.

Though about the best you can see (in recent electrical generating plants) is right around 50%, up from around 35% thirty years ago.

A good part of this is actually due to the piston engine: roughly a fifth of the heat energy developed inside the cylinder with every firing is needed to exhaust the combustion gases out the exhaust valve. This is one reason aero engine makers stopped developing piston power about the end of WW2 and the turboprop engine came out, and this is also why turboprop engines are small, shaft horsepower for shaft horsepower.

Turbosupercharging came around as one way to scavenge some of that thrown-away heat energy. Handling a lot of turbosupercharging power was the reason the WW2 Thunderbolt was so bulky a fighter plane; it was full of ducts, behind a great big two-row radial engine.

Tiny turboshaft engines for automobiles probably best suit an electric powertrain, though: spin an alternator, not a transmission and driveshaft, feeding two or more electric motors turning the wheels. It works for locomotives...