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Old 02-25-2019, 10:11 AM   #1 (permalink)
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Information needed for Pulse and Glide

I've been musing about the benefits and drawbacks of P&G (which I am new to) and it occurred to me that I might not be seeing its full effect, if any, due to the lack of critical information about my car.

As I have understood it, the benefit of P&G is that you maximise the amount of time that the engine is operating in its most fuel efficient "zone" and coast for the rest of the time. I've managed to glean that the engine FE (or Brake Specific Fuel Consumption (BSFC)) is dependent on the engine RPM and output torque as it is related to optimum engine temps and frictions I'm assuming. This gives me only the engine RPM to control the FE from the driver's seat at any given driving speed and condition, hence the "revving up" to desired RPM and then gliding.

So that brings me to the question: Isn't it a prerequisite that I know where my car has its optimum RPM for any given torque load, i.e the BSFC map, and won't I just be winging it without that information? I've found that the i10 has its max torque at 4500 RPM, but this doesn't necessarily mean its peak FE is there right?

Can anyone clarify this? Am I better just going for constant low speed/ high gear instead?

PS: If anyone has a BSFC map for a Hyundai i10 (2011) that would be grand!

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Old 02-25-2019, 10:57 AM   #2 (permalink)
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https://ecomodder.com/forum/showthre...d-19594-5.html

Old thread on P&G, I doubt you'll want to rev past 2500. And IMO if not willing to go Engine Off in the coast I don't think it will save anything over going a constant average speed of the average P&G.

Last edited by roosterk0031; 02-25-2019 at 11:06 AM..
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Old 02-25-2019, 11:03 AM   #3 (permalink)
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I only do mini-pulse and glides where downhills allow me to glide for longer than I would on flat, and I just put the clutch in rather than kill the engine. Doesn't really save that much.

Also, if anyone is behind me I don't subject them to inconsistent speed. They will get worse fuel economy because they aren't prepared for the speed changes.
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Old 02-25-2019, 01:38 PM   #4 (permalink)
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Quote:
Originally Posted by redpoint5 View Post
I only do mini-pulse and glides where downhills allow me to glide for longer than I would on flat, and I just put the clutch in rather than kill the engine. Doesn't really save that much.

Also, if anyone is behind me I don't subject them to inconsistent speed. They will get worse fuel economy because they aren't prepared for the speed changes.
I would shift to neutral and let the clutch out while gliding, otherwise you're subjecting your throwout bearing and spring to far more use than it's designed for.
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Old 02-25-2019, 05:17 PM   #5 (permalink)
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With such a small engine it only makes sense to P&G at lower speeds.

I used to pulse between 2000 and 3500rpm. And learned over time that it was more important to reach the next coast point at the right speed than to load the engine optimally.
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Old 03-06-2019, 09:24 AM   #6 (permalink)
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Quote:
Originally Posted by roosterk0031 View Post
https://ecomodder.com/forum/showthre...d-19594-5.html

Old thread on P&G, I doubt you'll want to rev past 2500. And IMO if not willing to go Engine Off in the coast I don't think it will save anything over going a constant average speed of the average P&G.
Thanks! They seem to be touching on the point that you need to know the optimum BSFC "island" in order to gain the most from P&G, but it's not stated explicitly. I also agree that the benefits seen in my car will be minimal at most
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Old 03-06-2019, 09:27 AM   #7 (permalink)
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Quote:
Originally Posted by redpoint5 View Post
I only do mini-pulse and glides where downhills allow me to glide for longer than I would on flat, and I just put the clutch in rather than kill the engine. Doesn't really save that much.

Also, if anyone is behind me I don't subject them to inconsistent speed. They will get worse fuel economy because they aren't prepared for the speed changes.
Yeah I've also started doing that lately since it seems that I'm "driving blind" without knowing my engine's best operating point. Also it can be quite fun to try and hit perfect runs in hills and valleys
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Old 03-06-2019, 09:30 AM   #8 (permalink)
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Quote:
Originally Posted by Shaneajanderson View Post
I would shift to neutral and let the clutch out while gliding, otherwise you're subjecting your throwout bearing and spring to far more use than it's designed for.
That's actually related to another worry of mine, namely the downsides of P&G. No matter how smooth I release the clutch there's always that slight "snag" which I don't imagine is good for the mechanics in the long run.

Also, a more serious issue is that my concentration on the road is impacted since I'm having to keep an eye on the speedometer. Not good at all!
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Old 03-06-2019, 09:34 AM   #9 (permalink)
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Quote:
Originally Posted by jakobnev View Post
With such a small engine it only makes sense to P&G at lower speeds.

I used to pulse between 2000 and 3500rpm. And learned over time that it was more important to reach the next coast point at the right speed than to load the engine optimally.
Interesting... Once I get my OBDII logger up and running I'm planning on creating my own "MPG map" with logged MPG values plotted against driving speed and engine RPM. Hopefully that will inform me on the optimal RPM at any given speed.
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Old 03-07-2019, 11:18 AM   #10 (permalink)
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Quote:
Originally Posted by Telemachos View Post
That's actually related to another worry of mine, namely the downsides of P&G. No matter how smooth I release the clutch there's always that slight "snag" which I don't imagine is good for the mechanics in the long run.

Also, a more serious issue is that my concentration on the road is impacted since I'm having to keep an eye on the speedometer. Not good at all!
I wouldn't so much worry about wearing out the clutch on your bump restarts, that little bit of slip is no more than you would normally have when shifting gears. It is what the clutch is designed to do afterall.

however the throwout bearing and clutch spring are not designed to be held long term. For that matter why strain your leg constantly when it's a simple matter to put the transmission in neutral.

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bsfc, doing it wrong, hyundai, p&g, pulde and glide

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