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Discussion Starter · #1 · (Edited)
I have been really easy on the car trying to get the best economy and i always let it shift at 2k RPMS or less. I guess i have been doing it all wrong. I found a post on another site saying differently.

Post #5
I have read that
BMW instructs drivers to accelerate at 75% engine load and shift when the
engine's mean piston speed reaches 1200-1500 feet per minute. Mean piston speed
is a function of engine stroke and RPM.

Vp=RPM*S/6

Vp= mean
piston speed
RPM= engine speed
S= engine
stroke length, inches

This keeps you in
closed-loop operation (for EFI) at high volumetric efficiency with low
frictional horsepower loss for as short a time as possible before you can
achieve steady-state cruise and/or EOC. It is what I like to say is accelerating
"smartly."


Chevy Cruze 1.4 stroke is 82.6 mm or 3.3 in. I did the math and came up with 2182-2700 RPMS is the optimum rate of acceleration for fuel efficiency.


Lets discuss,
 

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To my understanding with open/closed loop. You are only in open loop while your warming up you engine after its at operating temp it will switch over to a closed loop and stay there. So I don't under stand when u say "keep you in closed loop"

Dealing with RPMs I still say that under 2k is better in city and right at 2k on highway. This has been my best results
When I go over 2k in city I always see a drop in mpg.


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To my understanding with open/closed loop. You are only in open loop while your warming up you engine after its at operating temp it will switch over to a closed loop and stay there. So I don't under stand when u say "keep you in closed loop"

Dealing with RPMs I still say that under 2k is better in city and right at 2k on highway. This has been my best results
When I go over 2k in city I always see a drop in mpg.


Sent from iPhone 4
Car also goes into open loop under heavy throttle conditions. It determines AFR based on the most recent fuel trim before the heavy throttle condition, then adds extra fuel per the Power Enrich tables to bring it to anywhere between 11 and 13 AFR. This is done because there isn't a wideband O2 sensor to determine exact AFR at all times.

Fuel usage calculations are also very inaccurate while the car is in open loop.

Someone with a tuner would be able to tell us the exact throttle position when the car goes into open loop and the PE table is used, but it might not be of much use considering we have electronic throttle.

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Discussion Starter · #4 ·
I do have the torque app and dongle, ill check and see if it shows open/closed loop.
 

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So is it possible just to switch out the reg o2 with a wide-band o2. Or does it require a computer to use it with another port in the exhaust .

I believe I've seen someone do it to a old corvette on "2 guys garage" or some other show. But don't remember if it was just a direct swap or more to it.



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So is it possible just to switch out the reg o2 with a wide-band o2. Or does it require a computer to use it with another port in the exhaust .

I believe I've seen someone do it to a old corvette on "2 guys garage" or some other show. But don't remember if it was just a direct swap or more to it.

Sent from iPhone 4
No, unfortunately its not. Unless you find a way to modify the harness, WB o2 sensors are 6-wire harnesses. You'd be better off adding a bung for a WBO2 system and leave the original be, that one does have a job to do.
 

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No, unfortunately its not. Unless you find a way to modify the harness, WB o2 sensors are 6-wire harnesses. You'd be better off adding a bung for a WBO2 system and leave the original be, that one does have a job to do.
Actually, it is possible. It requires the use of a controller interface. Short story, its a box that the wideband O2 plugs into, which converts the signal into something that the PCM can read as well as providing a signal for your digital gauge. However, you're looking at $500+ worth of equipment here.

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On level road from sea level to 3500-4000ft, I suspect that XtremeRevolution's shift points of

1-2: 2000 RPM
2-3: 1800-2000RPM
3-4: 1500RPM
4-5: 1500RPM
5-6: 1500RPM

are reasonably close to the optimum shift points for acceleration, especially since he has reported being able to hear the turbo starting to spin up at 1500 RPM. Above 4000 ft you need to increase these shift points by about 300 RPM to account for lower air density, which puts the shift points at 5000-7000 ft right at the low end of OPs calculated shift points. When travelling downhill you can upshift as soon as the shift won't push the engine speed below idle RPM. Uphill can require shifting at significantly higher RPMs to keep enough torque to continue accelerating. Today, while resuming the posted 65 MPH after a 25 MPH bottleneck driving up the west side of Vail Pass required shift points between 3500 and 4000 RPM. Shifting lower doesn't provide enough torque and HP to accelerate after the shift. I had to downshift from 3rd to 2nd to get started after the bottleneck ended, bascially setting the engine speed above 2500 RPM to start accelerating.

BMW's formula is for a non-turbo charged car and thus doesn't take into account the additional torque and HP boost from the turbo charger, which why for the best fuel ecoomy we can and should shift our ECO MTs at lower shift points than the BMW formula.
 

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On level road from sea level to 3500-4000ft, I suspect that XtremeRevolution's shift points of

1-2: 2000 RPM
2-3: 1800-2000RPM
3-4: 1500RPM
4-5: 1500RPM
5-6: 1500RPM

are reasonably close to the optimum shift points for acceleration, especially since he has reported being able to hear the turbo starting to spin up at 1500 RPM. Above 4000 ft you need to increase these shift points by about 300 RPM to account for lower air density, which puts the shift points at 5000-7000 ft right at the low end of OPs calculated shift points. When travelling downhill you can upshift as soon as the shift won't push the engine speed below idle RPM. Uphill can require shifting at significantly higher RPMs to keep enough torque to continue accelerating. Today, while resuming the posted 65 MPH after a 25 MPH bottleneck driving up the west side of Vail Pass required shift points between 3500 and 4000 RPM. Shifting lower doesn't provide enough torque and HP to accelerate after the shift. I had to downshift from 3rd to 2nd to get started after the bottleneck ended, bascially setting the engine speed above 2500 RPM to start accelerating.

BMW's formula is for a non-turbo charged car and thus doesn't take into account the additional torque and HP boost from the turbo charger, which why for the best fuel ecoomy we can and should shift our ECO MTs at lower shift points than the BMW formula.
Might also be worth noting that those shift points are for the Cruze Eco with the MT transmission. They may not be suitable (or available) by manual shifting an auto transmission, and they may be different with other non-Eco MT Cruzes.

Using those shift points with a calculated 76% city driving split, I've sustained a 40mpg lifetime average and my current tank may break my best record of 44.7mpg (which was also achieved with a ~75% city split).


I do have the torque app and dongle, ill check and see if it shows open/closed loop.
I would like to mention that the trigger for open loop mode will be a combination of both throttle position and RPM. I don't believe it is reliant on throttle position alone.
 

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it's possible that, with my 1.6 gpl, 81.5cm stroke, I have to change somwere between 2600 and 3300 rpm? or I did sometihng wrong? what i have to consider with gpl ?
 

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I do have the torque app and dongle, ill check and see if it shows open/closed loop.
it's possible that, with my 1.6 gpl, 81.5cm stroke, I have to change somwere between 2600 and 3300 rpm? or I did sometihng wrong? what i have to consider with gpl ?
It's certainly possible, but I would advise a lower shift point for fuel economy.

Can you re-phrase your last question?
 

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Discussion Starter · #12 ·
I played with torque a little, It takes a lot of throttle to change open/closed loop.

What info do you want or what do you want to see?

55 mph screen shot.


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Might also be worth noting that those shift points are for the Cruze Eco with the MT transmission. They may not be suitable (or available) by manual shifting an auto transmission, and they may be different with other non-Eco MT Cruzes.
Since we're only talking about shift points, I think the RPM ranges are close to optimal for all Cruzen with the 1.4T engine, regardless of the transmission. The 1.8 is a different engine and may require different shift points.
 

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it's possible that, with my 1.6 gpl, 81.5cm stroke, I have to change somwere between 2600 and 3300 rpm? or I did sometihng wrong? what i have to consider with gpl ?
Which cruze engine is this? Or is it a different car completely? Also, I have never seen a car that gets it's best fuel economy shifting that high. I have seen cars and situations where you need to shift in the range you're giving to avoid being a traffic hazard.
 

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Since we're only talking about shift points, I think the RPM ranges are close to optimal for all Cruzen with the 1.4T engine, regardless of the transmission. The 1.8 is a different engine and may require different shift points.
Well, here's my reasoning behind that. The only reason why I shift so high in 1st and 2nd is in order to be in a decent RPM/powerband in the following gear. If I had shorter gears, I'd be shifting 200-300rpm lower.
 

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Well, here's my reasoning behind that. The only reason why I shift so high in 1st and 2nd is in order to be in a decent RPM/powerband in the following gear. If I had shorter gears, I'd be shifting 200-300rpm lower.
Agreed. Also, I've noticed that in many cases I physically can't work the clutch fast enough for a lower shift from 1-2. My leg simply doesn't move that fast.
 

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Agreed. Also, I've noticed that in many cases I physically can't work the clutch fast enough for a lower shift from 1-2. My leg simply doesn't move that fast.
If I were to shift according to the light, I'd be rowing the lower gears literally every second.
 

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If I were to shift according to the light, I'd be rowing the lower gears literally every second.
I almost never see my shift up light and when I do it's because I'm at the border line but know that I need to stay where I am for torque. 25 in 3rd on a hilly dirt road for one place - if I shift up I won't make it up the next hill.
 

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It's certainly possible, but I would advise a lower shift point for fuel economy.

Can you re-phrase your last question?
for a 1.6 fuel engine I use the formula and I reach the result 2600-3300 rpm, but with gpl I have less power then I suppose that I have to modify something in the formula adding or not something... or the rpm range given by the formula doesn't change with the horse power/torque?
by the way I usually shift below 3000rpm on flat road, below 2000 going down and after 3-3500 rpm going up

robermd said:
Which cruze engine is this? Or is it a different car completely? Also, I have never seen a car that gets it's best fuel economy shifting that high. I have seen cars and situations where you need to shift in the range you're giving to avoid being a traffic hazard.
I'm from italy, the first year chevy sold a 1.6 engine with gpl, but the engine was the old nubira's 109hp... this engine were sold only in italy :uhh:
 

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for a 1.6 fuel engine I use the formula and I reach the result 2600-3300 rpm, but with gpl I have less power then I suppose that I have to modify something in the formula adding or not something... or the rpm range given by the formula doesn't change with the horse power/torque?
by the way I usually shift below 3000rpm on flat road, below 2000 going down and after 3-3500 rpm going up


I'm from italy, the first year chevy sold a 1.6 engine with gpl, but the engine was the old nubira's 109hp... this engine were sold only in italy :uhh:
Your shift points may differ simply because you have an entirely different engine than we do.
 
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