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Old 06-23-2013, 08:26 PM   #1 (permalink)
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lugging kills my mileage

For my Subaru, I noticed that I get better fuel economy in a pulse if I make the same amount of power at higher rpm vs. lower RPM at wide open throttle plate.

In short -> 3/4 engine load at 2000rpm is better for me than full load (0 vacuum) at 1500rpm.

I have kept an eye on air to fuel ratio and they are always stoich so long as i don't exceed 3500rpm. the only difference I see on my instruments is higher ignition timing at higher RPMs / lower loads.

Monitoring the "horsepower" gauge and trying to maintain a steady power output has yielded better results than keeping a high engine load during the whole acceleration phase.

Just wanted to share my results and get some feedback. thanks!

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Old 06-23-2013, 10:28 PM   #2 (permalink)
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have you tried get up to the speed you want then switch to the highest gear possible.

once i get up to 60kph in 3rd i switch to 4th.
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Old 06-23-2013, 10:37 PM   #3 (permalink)
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There are a couple of things going on there.

First most engines have their best BFSC at about 2000 rpms give or take.

Second at full throttle most engines run a little rich to prevent detonation.
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Old 06-24-2013, 09:20 AM   #4 (permalink)
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get up to speed how? if you mean WOT then no, that gives me horrible mileage. anything above 3000rpm and my car really burns a lot of gas. high load and over 2500rpm it also burns a lot of gas. I found being gentle is the best. accelerating at 30kw power range.

Quote:
Originally Posted by TheEnemy View Post
There are a couple of things going on there.

First most engines have their best BFSC at about 2000 rpms give or take.

Second at full throttle most engines run a little rich to prevent detonation.
I certainly never go full throttle. just a 1/3 throttle is enough to achieve 0 vacuum at 1500rpm. but it seems it would be better to shift at say 2000rpm vs. 1500 from my experiments while making the same amount of power. the difference is not that great but its there...this is for around town driving though. on the highway I can pass without downshift due to the 4.11 final drive that puts me in 2500rpm at 65mph. but I found whether I pass at full load or ~70% manifold pressure doesnt make much difference at those speeds.

so in my notes higher loads are better at higher vehicle speeds while lower loads lead to better results in city driving.
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Old 06-24-2013, 12:50 PM   #5 (permalink)
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This should help you find your best acceleration load.
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Old 06-24-2013, 03:44 PM   #6 (permalink)
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ya unfortunately that requires a 4.06 firmware and two scangauges. I got neither

I have a full throttle engine dyno for my engine which determined 2400rpm to be most efficient. but im not sure how accurate it is since I heared its just an estimate.
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Old 06-24-2013, 10:54 PM   #7 (permalink)
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0 vacuum is for all intents and purposes full throttle, maximum dynamic pressure etc.

2400 rpm may very well be where your engine is most efficient at full throttle, where it is more efficient at lower throttles will take time and experimentation. That's why there is a BFSC chart for many engines

http://ecomodder.com/forum/showthrea...-got-1466.html
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Old 06-25-2013, 05:54 PM   #8 (permalink)
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but certain things like AWD torque distribution and valve lift is based on throttle input. Yes I know about BSFC charts but there is none for my engine as they are company secrets now. experimentation always has not delivered solid results. whether I shift at 1.5k or 3k 80% load I still get identical crappy mileage. but if I forget about engine speed and keep a constant power output of say ~40hp I get better mileage. its hard to maintain 40hp anywhere on the powerband except at ~2k rpm. below that it leads to full load and enrichment and above that power output shoots up and throttle becomes more sensitive.
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Old 06-29-2013, 07:58 PM   #9 (permalink)
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Quote:
Originally Posted by ever_green View Post
get up to speed how? if you mean WOT then no, that gives me horrible mileage. anything above 3000rpm and my car really burns a lot of gas. high load and over 2500rpm it also burns a lot of gas. I found being gentle is the best. accelerating at 30kw power range.



I certainly never go full throttle. just a 1/3 throttle is enough to achieve 0 vacuum at 1500rpm. but it seems it would be better to shift at say 2000rpm vs. 1500 from my experiments while making the same amount of power. the difference is not that great but its there...this is for around town driving though. on the highway I can pass without downshift due to the 4.11 final drive that puts me in 2500rpm at 65mph. but I found whether I pass at full load or ~70% manifold pressure doesnt make much difference at those speeds.

so in my notes higher loads are better at higher vehicle speeds while lower loads lead to better results in city driving.
Yea that's what I observed, trying to drive at only 1000rpm and shifting below 2000 didn't return very good gas mileage. I don't let the engine rpms get below 1500rpm if I need to accelerate at all. I tend to just give it the beans and hit 3000 or higher because my gearing is short, car is light, and it's kind of fun to do that in first.
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Old 06-29-2013, 11:16 PM   #10 (permalink)
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Quote:
Originally Posted by SentraSE-R View Post
Without instrumentation, you guys are just tossing WAGs for engine load. I've saved ~$2270 v. EPA on my xB, and ~$!500 v. EPA on my Sentra. That ~$3800 could buy 20 SGIIs and 20 UGs.

Efficiency log for: Mean Green Toaster Machine - 2006 Scion xB
Lifetime Fuel Economy: 49.4 mpg (US), 4.8 L/100 km, 59.3 mpg (Imp)
90-day Fuel Economy: 46.9 mpg (US), 5 L/100 km, 56.3 mpg (Imp)
3-tank Fuel Economy: 47.6 mpg (US), 4.9 L/100 km, 57.1 mpg (Imp)
EPA Combined Rating / % over rating: 28 mpg (US) / 67.3% (based on 90-day fuel economy)
Total fills: 121
Average cost per gal/L: $3.27 per gal (US); $0.00 per L (price data entered for 121 fill/s)
Average cost per fill: $24.61
Average distance cost: $0.07 per mi. / $0.04 per km
Total fuel used: 909.8 gal (US), 3444 L
Total distance traveled: 44898.7 mi. / 72257.5 km
Total cost: $2,977.61
Total fuel saved vs. EPA: 693.7 gal. (US) / 2625.9 L
Total saved: $2268.4 (based on avg. cost per gal./L)
Average tank distance: 371.1 mi. / 597.2 km

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Darrell

Boycotting Exxon since 1989, BP since 2010
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin
Mean Green Toaster Machine
49.5 mpg avg over 53,000 miles. 176% of '08 EPA
Best flat drive 94.5 mpg for 10.1 mi
Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg

Last edited by SentraSE-R; 06-29-2013 at 11:22 PM..
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