Quote:
Originally Posted by MGB=MPG
i used to get in top gear as soon as possible with very light throttle loads , however im told thats wrong.
the advice was accelerate briskly [about 80% power] fully utilizing the peak torque segments of YOUR engines power curve in all gears then at cruise around about peak torque for your engine .i go into top gear [4] at about 40MPH and thats some pretty fast stick whipping at 80% for sure
not to say you should red line the thing in the low gears. but run it up until you can fall into the next gear at a good torque #
a power curve chart [fuel-power] is helpful in deciding the best engine speed shift points
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Mind you I only know the theory of driving stick, and can't actually do it, but peak torque doesn't really mean peak efficiency, since torque has more to do with the volumetric efficiency provided by your intake and exhaust acoustic resonance and cams.
Light throttle acceleration is definitely bad, but what engine speed do you use? It's hard to find BSFC charts but out of all the ones I've ever managed to dig up BSFC is in a "very good" range between 2000-3000 on most engines. That's not to say going outside that range is necessarily going to make a noticable impact, but using somewhere between 2-3krpm to accelerate would appear to be ideal for most cars. I imagine as you go up in displacement per cylinder that number goes down since the cooling losses are comparatively smaller with a large combustion chamber.
Also the higher you rev, the more energy the rotating assembly, flywheel, and input shaft soak up, which may or may not be significant, I never bothered to figure out the order of magnitude of those losses.
I guess there's also the issue of "throttle %". You'd have to know how your engine requested torque vs. pedal position is calibrated if it's drive by wire throttle, but I think if you just press halfway down you'll get something like 50-70% torque which is pretty good. With a cable throttle it's harder, and it'd be good to have a manifold vacuum gauge or something, and aim for 0.7 bar absolute pressure or somewhere around there.