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Originally Posted by SilveradoMike
Im still having trouble understanding how improving power (mostly low end torque) wouldn't translate to an increase in mpg. Letting the engine make the same amount of power eaiser or at a lower rpm seems to make sense in my head. My thinking is this. If you have two identical trucks with idenical loads and total weight. But one has 500hp/tq and the other has 250hp/tq. Wouldnt the one with more power be able to do the job eaiser? There for reducing load on the engine and thus decreasing throttle input/fuel usage? Both being driven same route/speed ect.
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That's because you are talking peak hp rather than the hp used at that specific RPM/throttle position/load.
If you need 200hp to accelerate your loaded-up, gas-powered truck and you have one truck that makes 500 peak hp and one that makes 250 peak hp, the 250hp truck will likely be more fuel efficient. Why? The throttle will be nearly wide open on the less powerful engine, while the 500hp engine will be more closed. So, the cylinders will be acting against a significant vacuum in the intake manifold because the throttle plates are blocking air flow. It will take less of the available capacity on the 500hp engine, so there will likely be less stress on the engine and tranny (which would presumable be designed to handle higher loads), but that doesn't mean better fuel economy.
Even better for economy would be to accelerate more slowly and only need 100hp. Still run the 250 peak hp truck at nearly WOT but at lower rpms.