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Old 01-04-2013, 11:08 PM   #1 (permalink)
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Stay in best BSFC zone even if torque converter slips?

I have been playing with accelerating efficiently and I've realized that I can make my tranny shift into third quickly, then get on the throttle and hold 2500 RPM at 65-70% load. This results in fairly brisk acceleration. About 45 mph I can just let off the throttle and it upshifts and locks the torque converter.

Although I don't have a BSFC Diagram for my engine (2.0L "Beta II" in many hyundais and kias), I assume that this RPM/LOAD is near the best efficiency point. But I can't help but wonder if it is allowing the torque converter to slip too much and is undoing any extra efficiency the engine might be gaining. Whereas operating at a lower load level might result in less slippage, possibly meaning that the entire BSFC diagram for the drivetrain system gets shifted "downwards" to lower load levels.

In other words, unlike a manual transmission, I think the efficiency of the engine and automatic tranny must be considered together to make the BSFC diagram useful.

Any thoughts? Trying to avoid a detailed investigation into something that others have already figured out! (And save the gas I'd have to burn!)

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Old 01-05-2013, 02:32 AM   #2 (permalink)
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Probably should figure out if the torque converter ever locks in lower gears. I think higher rpms = higher torque converter efficiency, but don't quote me on that one, it's just a hunch based on driving my mom's car.

I don't know if this is actually working, but when I drive an automatic I press the gas lightly to start, roll onto the pedal halfway as the car picks up speed, and as the rpm approaches 3000 I let off a little to coax a shift and then back on it a little, and then I take note of the rpm; Sometimes the transmission doesn't want to shift up, so I switch to neutral and then back, usually that coaxes an upshift, and then I put very little pressure on the pedal to keep it in the highest gear.

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