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Old 08-19-2016, 04:09 AM   #1 (permalink)
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Noob questions about pulse and glide

Hi I was wondering if pulse and glide will still be efficient with the engine on? as i cant really turn off the engine here because of the needed demand on airconditioning (humid and hot here) or will dwl work better?

also when slowing down to a slow pace is it better to use dfco or just put it in neutral?

another question is if its better to stay at the best bsfc at a lower gear (say 2500 rpm 2nd gear hi load) compared to lets say 2000 rpm 3rd gear hi load but not in the "best island" in the bsfc.

thanks!

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Old 08-19-2016, 07:40 AM   #2 (permalink)
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Frankly, no one can answer those questions for you. You'll just have to fine tune your technique for your car and conditions.

In summer I EOnC in neutral, so I can keep the A/C (A Prius is great for hot weather BTW).

If you look at BSFC maps you really don't loose much efficiency by not being perfectly on the island, it's a few percent so I don't worry much about it, I just try to stay near 80% load (NA petrol cars).
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Old 08-19-2016, 07:50 AM   #3 (permalink)
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Most of my P&G is with the engine on. It's as simple as popping out of gear and watching the instant mpg skyrocket.

At 60 mph my car settles down to 270-300 mpg. It's not off, but it's nothing to sneeze at.
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Originally Posted by sheepdog44 View Post
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 08-19-2016, 08:15 AM   #4 (permalink)
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Think about it like this, the engine consumes more power the faster it spins because that's how friction works. By putting it in idle, you're slowing the engine down and reducing its energy consumption, so yes, it generally works.

It might not work on certain cars with extremely tall gearing on flat terrain. If your cruise rpm is like 1500 (e.g. Corvette) I would guess that engine on pulse and glide doesn't do much. However if you see a hill, that's a good opportunity to drop it in neutral on a slight downgrade.
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Old 08-19-2016, 09:54 AM   #5 (permalink)
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Quote:
Originally Posted by escymkii View Post

also when slowing down to a slow pace is it better to use dfco or just put it in neutral?
If you have to slow down it is best to slow in neutral. The trick is to throw it into neutral early enough that you will be down to the target speed at the right time.

For example: if you know the speed limit decreases ahead find the spot where you can coast in neutral from and reach the slower speed zone at the reduced speed limit. This way you are throwing away less of the energy that was used to get up to speed in the first place.

Neutral, DFCO, brakes {last resort }
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Old 08-21-2016, 09:52 PM   #6 (permalink)
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Hi thankyou for your responses! its quite hard really to have an economical figure here because there are lot of speed bumps! i think every 200m to 300m. i get 18km/l tops when cruising on long trips but get a horrible 6-8km/l at city driving despite P&G because of the speed bumps and awful traffic. well looks like ill modify my P&G at a lower rpm and more load thanks!
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Old 09-15-2016, 07:31 PM   #7 (permalink)
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got a noob question about P&G...

Started to do the gas it up above the speed limit, push the clutch in to glide, repeat. When you pulse back up to speed, should you accelerate as fast as possible back to speed? Or should you ease the acceleration up?
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Old 09-15-2016, 08:45 PM   #8 (permalink)
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Here's a BSFC chart for my engine:




I generally drive at 50mph when the speed limit is 50 or above, which puts me right at 2000RPM, where the engine can most efficiently convert fuel into motive energy. From the chart, you can see that above ~75% load, efficiency begins to drop off, so it's best to accelerate at high but not full load.

I have a $3 eBay ELM327 bluetooth dongle paired with my smartphone I used to keep an eye on load until I got a feel for it.
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Old 09-15-2016, 08:51 PM   #9 (permalink)
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thanks for the reply. you guys really know your stuff. A lot of it is well above my head. I def need to do some driving experimenting to find my efficiency sweet spots.
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Old 09-15-2016, 09:05 PM   #10 (permalink)
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Perhaps a more helpful tip would be that, when I do P&G, I pulse in top gear at medium-acceleration. Given that I live in a very hilly/mountainous area, my pulses generally coincide with climbing one side of a hill, while my glides I do with the engine off down the other.

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