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Old 08-20-2012, 02:27 PM   #11 (permalink)
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I'd say P&G won't, only way P&G is effective is if you cant get 70% or higher engine loading, with your automatic it will probalby down shift at 30-40% if anything close to my 2 GM's. Sentra SE-R did testing with his car with different engine loading using P&G.

http://ecomodder.com/forum/showthrea...d-19594-2.html

With his car 70% load during the pulse, and engine off during coast is need to break even vs constant speed. I'm pretty sure that's impossible with a GM auto you can't get 50% load unless your REV's are way to high to be affective. And you probably won't be going engine off, 09-10 Cobalts auto's do allow flat towing so maybe your's does, but would be a lot of wear on the starter.

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Old 08-20-2012, 04:03 PM   #12 (permalink)
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Your model + your powertrain + your foot + your roads = your answer. Get an SG or UG to find the answer that works best for you.

I do pretty well P&G with our minivan, better than constant speed. This one does have an eco button- it makes the trans not want to downshift, making P&G a lot easier.
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Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

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Old 08-20-2012, 04:20 PM   #13 (permalink)
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With gliding and no pulsing you can improve easily on just constant speed. A lot depends on the terrain but i glide about 25% of the distance traveled with it in neutral.
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Old 08-20-2012, 04:20 PM   #14 (permalink)
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Quote:
Originally Posted by roosterk0031 View Post
I'd say P&G won't, only way P&G is effective is if you cant get 70% or higher engine loading, with your automatic it will probalby down shift at 30-40% if anything close to my 2 GM's. Sentra SE-R did testing with his car with different engine loading using P&G.

http://ecomodder.com/forum/showthrea...d-19594-2.html

With his car 70% load during the pulse, and engine off during coast is need to break even vs constant speed. I'm pretty sure that's impossible with a GM auto you can't get 50% load unless your REV's are way to high to be affective. And you probably won't be going engine off, 09-10 Cobalts auto's do allow flat towing so maybe your's does, but would be a lot of wear on the starter.
With my 02 pontiac i can hold to the engine load steady at just about any load %
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Old 08-20-2012, 05:48 PM   #15 (permalink)
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Quote:
Originally Posted by 3-Wheeler View Post
Universities use this same P&G method to achieve mpg readings of over 2000 and higher. Slow speeds and lot's of engine off coasting.
Sure, but they are freewheeling like a bike then - even shutting down the engine.

If his auto transmission doesn't have a freewheeling of coasting function , it will be effectively braking.



One way to find out : Try it
Set speed using CC
From a fixed point, let go of the gas and see how far it rolls.
Return
Get up to speed using the resume function
From the very same point, let go of the gas and shift into neutral just for once.
See how far it rolls now.
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Old 08-20-2012, 05:53 PM   #16 (permalink)
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You can accelerate at 1500 rpm to 2100 at +90% load in OD and not have it unlock the torque convertor and/or downshift?

I've wonder if SGII & untraguage measure load% way differently.
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Old 08-20-2012, 06:07 PM   #17 (permalink)
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Automatic.

In my Odyssey I can get 10-20% better highway mileage using P&G, where glide = neutral. If you're not willing to use neutral, just stick to steady speed. The engine braking from in-gear "gliding" will cost you dearly.
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Old 08-20-2012, 06:33 PM   #18 (permalink)
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But my 2 GM auto's coast same OD or Neutral, isn't the point of P&G to be efficient you need to get engine load fairly high 70%+ but RPM's low, the GM's unlock at lower rpm before I can ever load them in drive or OD unless rpms are way up.

In Sentra's data collecting (only one car) P&G at 70% load with EOC to roughly match constant speed. He had to go higher load still with EOC to get better than constant speed. With my auto GM's and I highly suspect a Cruze it's impossible to get better than 70% load in top gear without going 90 mph, I doubt I can get 40% at 2,000 rpm without downshifting.

I believe your honda's lack of free wheeling is why P&G does better than constant speed. Both the malibu and Impala drop to 1000 rpm when going down hill and will pick up speed.
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Old 08-20-2012, 07:18 PM   #19 (permalink)
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Don't shift into nuetral in an automatic it's never worth it. Please don't even try to do it you'll thank yourself later.

P&G in gear will only be beneficial if you can turn the engine off while your coasting in gear which is one thing. In gear your coast will never be as long as if you were in nuetral. The length of your coast in relation to the length of the pulse will be a good indicator if it'll be worth it. But if you cant turn off the engine in your coast your gains will be marginal if not worse.

What I think your getting at is driving with load, which is the best thing you can do in an automatic. Accelerate downhills, lightly coast in gear at the bottom flat slowly killing your speed to the target cruise mph. If you have to accelerate do it before a hill or cruise at a higher speed in anticipation. Never accelerate uphill! Drive slower. Accelerate less to a lower speed and cruise at the slowest speed in the highest gear you can get the AT into. Pump up your tires.

Those are good gains to be had by simply driving with load. My old Saab did 26mpg normal driving, I got it up to 30mpg by changing the nut behind the wheel.

Just my opinion.

For Manual cars P&G is always better. Not every car has the luxury of leanburn, and in the case where your car doesnt leanburn (which is the vast majority,) your gains will be even greater than maintaining speed.
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Old 08-20-2012, 08:43 PM   #20 (permalink)
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Sheepdog, agree with most of what you said, except never try coasting in N, my Dodge must be in N to coast well. Best gains made are with the Nut, but it is different between makes of cars. If Honda don't unlock N coast can gain, my Dodge unlocks if coasting down a big hill, but then engine revs to 3k if driving on cruise which I do 95% of time if the car of the day has it. My auto GM's coast like in N, my manual GM, 5th gear off throttle going down a small Iowa hill that will barely maintian speed is 120 mpg in 5th, 180 mpg neutral coast, plus neutral coast will hold or pickup speed.

The OP is talking GM, and I think with GM auto's set the cruise at 55 and forget. Accelerate hard as you can without reving past 2300 rpm or so since he has the 1.8, start your coast earlier than you think you should and you'll bet EPA combined by 40-50%.

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