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Old 04-08-2013, 10:33 AM   #1 (permalink)
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lower engine load better for MPG, torque converter to blame?

My car allows me to accelerate with a locked up torque converter above 40mph with approximately 50-60% engine load at 1800rpm according to my scangauge. However below 40mph the torque converter is always unlocked or slipping (unless decelerating) so i havent noticed improvement with lower load acceleration. But for above 40mph every test i did shows locked acceleration at low loads is better than unlocked or slipping TQ at 80% plus loads. However instruments are not always accurate and i was just wondering what other people with auto transmissions think about this? Are torque converters the bigger problem compared to engine pumping loss associated with smaller throttle opening? Someone told me my car isnt subjected to traditional pumping losses because of variable valve lift system.

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Old 04-08-2013, 11:38 AM   #2 (permalink)
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Get above lock speed with high load and stay above that speed. Besides we all know high load accel is best NOT low load.
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Old 04-12-2013, 04:36 PM   #3 (permalink)
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with the torque converter fully unlocked my engine speed jumps to around 3000-3500rpm under load. At 3500rpm my ECU enriches the mixture. after some experimenting i managed to trick the TCU to keep the TQ locked using the throttle while increasing engine load to about ~95% at 1500rpm. you just have to slowly open the throttle, something to do with the drive by wire system. if you just step on the throttle (even if your only apply a bit of throttle) the torque convert will start slipping and RPMS jump. I found 1500rpm (TQ locked) and ~95% engine loads to give me best results but if anyone thinks i can improve on this to reach my 30mpg city goal please let me know.
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Old 04-12-2013, 10:35 PM   #4 (permalink)
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Exactly why nobody here likes automatics. If the converter is unlocked any additional load just revs the engine higher. Personally, I accelerate moderately in first to about 15mph/2200rpm, let it shift to 2nd then get on it at high load and reach 40+/3800rpm and stay in lockup the rest of the way up.
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Old 04-12-2013, 11:01 PM   #5 (permalink)
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the Jetta is DSG = no torque converter

the jetta hybrid is DSG
so there is no torque converter
like is used in an automatic and will easily exceed 30mpg
the jetta has a "glide" function where the drivetrain is disengaged from the engine for a "Power on coast" type of function

the subaru ?
can be tricked (as you have discovered) as rate of change in TPS value is a primary input to unlock the torque converter

the only real fix to to replace the car with an automatic trans to one with a manual trans
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Old 04-13-2013, 12:08 AM   #6 (permalink)
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Quote:
Originally Posted by ksa8907 View Post
Exactly why nobody here likes automatics. If the converter is unlocked any additional load just revs the engine higher. Personally, I accelerate moderately in first to about 15mph/2200rpm, let it shift to 2nd then get on it at high load and reach 40+/3800rpm and stay in lockup the rest of the way up.
3800rpm? that seems a bit high - at least for my subaru above 3k rpm it really starts to burn a lot of gas. but yea i guess that minimizes time Not spent in overdrive/coasting. i'm really starting to do a lot of coasting if traffic permits. I need another 4mpg to reach my goal but ill be glad with just 28mpg.

Quote:
Originally Posted by mwebb View Post
the jetta hybrid is DSG
so there is no torque converter
like is used in an automatic and will easily exceed 30mpg
the jetta has a "glide" function where the drivetrain is disengaged from the engine for a "Power on coast" type of function
haven't got the jetta yet but yes im just glad it's not a cvt or conventional auto with torque converter. after reading the jetta manual though it recommends to stay off boost and drive in eco load. that means less engine load correct? or does it have something to do with running on battery.
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Old 04-13-2013, 02:40 AM   #7 (permalink)
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Mod to make it easier to keep a car in lean burn:

AutoSpeed - Giving the Insight a Good Driver

Something similar might help keep the TC locked.
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Old 04-13-2013, 10:39 AM   #8 (permalink)
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Quote:
Originally Posted by ever_green View Post
3800rpm? that seems a bit high - at least for my subaru above 3k rpm it really starts to burn a lot of gas. but yea i guess that minimizes time Not spent in overdrive/coasting. i'm really starting to do a lot of coasting if traffic permits. I need another 4mpg to reach my goal but ill be glad with just 28mpg.
I can do 15-40mph in about 4-5 seconds in 2nd. Its probably a toss up between that and using 3rd.

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