How to accelerate in P&G mode? - Fuelly Forums

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Old 06-04-2008, 01:03 PM   #1
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How to accelerate in P&G mode?

I'd like input from people with experience with optimal acceleration when in Pulse and Glide (keeping the engine ON in glide).

What's your real world experience on that topic? How hard to accelerate in P&G mode?


FE recommendations are to accelerate as slow as possible, in low RPMs. I believe the logic is you don't know what you're doing so we'll give you an idiot proof solution yet not optimal: low RPMs=less gas used. The recommendation also likely assumes you keep using a lot of gas once you've accelerated. HOWEVER, in P&G, the goal is to save gas on the total distance travelled, and in G mode gas used is little.

Let's set the rules here:

- Total distance is split in P-distance and G-distance.
T = P + G
- In G, car uses constant 700RPM, and burns a typical 0.3GPH.
- Total travel time is constant no matter what (else you could drive slower meaning higher FE in theory)
- City travel < 45MPH so aero impact negligible

My take is the best way to accelerate is a hard acceleration where the engine is in it's peak torque curve, so that distance P is minimized, in favor of G, and that doing so the engine runs at peak performance aka energy burned vs enrgy output to the wheels.

With the above, if we can plug in GPH for some accelerations and acceleration durations, we could tell what's optimal. However I don't have the data...
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Old 06-04-2008, 01:21 PM   #2
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I've been having great luck in my manual transmission car using WOT in the highest gear possible, though in cars that go to open loop mode under WOT it would be better to use 80% open throttle.

In my automatic, I use about as much pressure on the gas pedal as I can without causing it to downshift. For sure it is accelerating far less efficiently in 2nd gear under any amount of throttle than in 3rd gear.

Take a look at the fuel rate monitor thread linked in my sig, you can get a gauge that represents your GPH. A ScanGauge can't measure your GPH, it only guesses based on a calculation of MAF, O2, TPS, and other sensors.
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Old 06-04-2008, 01:33 PM   #3
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Hmmm.. But in 2nd gear, you accelerate darn fast, so you're in acceleration mode less longer. For example you could be burning 50% more gas in P mode but need to do it for 1/2 the time before going into G mode.

You have to add time to the equation. That's why for me the equation is hard to figure out!

As for the "DIY fuel rate monitor" thread, I'd like to do that on my Del Sol, it's OBD-1 so no SG anyway. Someone posted a system with a wire connected to the PC audio port to collect duty cycles with a Java applet. I think it's a great idea, and wanted to do that but have yet to figure out what to tap where w/o messing up the car. I also have ideas on how to extend that to allow detailed experiments and conclusions. Pics of the tap setup would be great to get an idea of how it was done (but that's all off topic).
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Old 06-04-2008, 02:14 PM   #4
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http://www.autospeed.com/cms/A_110216/article.html

High throttle, low rpm is best. Get the most efficient power out of the engine.

But... I'm finding that from a complete stop up to maybe 20mph, super light throttle ends up better. Then, when I'm closer to the desired speed, I switch into a heavy-throttle P&G routine.
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Old 06-04-2008, 03:25 PM   #5
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I just go by sound;Automatic 4 speed BTW..... When accelerating I listen for the steady increase in RPMs and a nice smooth gear change, then the same repeated for the next gear.
When cruising at highway speed ( or my version there of) I listen for a certain up/down sound almost as if the transmission was slipping.Then shift to neutral when I feel I'm going fast enough for a good glide.
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Old 06-04-2008, 03:30 PM   #6
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Quote:
Originally Posted by sonyhome View Post
You have to add time to the equation. That's why for me the equation is hard to figure out!
I figured for time. When the total acceleration is done, it's always been better for me to use a higher gear and lower RPM.

Quote:
Pics of the tap setup would be great to get an idea of how it was done (but that's all off topic).
I could post pics, and I think monroe74 or fumesucker did (and I'm pretty sure it was fumesucker who hooked it up to his PC's sound card), but it's so incredibly simple that you really don't need pics. Your fuel injectors are probably kinda near your spark plugs. When you look at fuel injectors, you'll see that each has two wires going to it; one of the wires will be the same color for all, and the other wire will be a different color for each injector. Use the wire that's different.

Quote:
Originally Posted by PaleMelanesian View Post
But... I'm finding that from a complete stop up to maybe 20mph, super light throttle ends up better. Then, when I'm closer to the desired speed, I switch into a heavy-throttle P&G routine.
Accelerating from a stop, you're in very low gears with very fast acceleration and it's hard to control your RPMs and shifting fast enough. At least, that's what I've found with WOT in my manual tranny, and in my auto of course a quick stab of the gas pedal will put me almost immediately into high RPM before I get a chance to let off the pedal.
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Old 06-04-2008, 03:59 PM   #7
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Best mileage in my Del Sol was 47. Pale does much better in a heavier car with the same basic engine tranny combination (I think).

Aero drag in city EPA cycle is 29%, highway is 70%, so aero is always a factor.

70% throttle in low enough gear to have your revs peak at 2200, then shift to higher gear.

Draft if possible, it's easy here with fairly heavy traffic.

Instead of EOC (which you stated you don't use, like me) here is an option.

Whenever you need to slow down use the highest gear practical to keep engine revs above 1000 RPM. I used to never downshift to slow down, but now I think it is a big factor in my mileage improvement.

If you know your traffic light patterns, try to time it so you don't have to decelerate more than a coast, but if you find your self having to stop for a light, try to use downshifting to stop all fuel delivery, which is the same as shutting the engine off (no fuel delivery).

I find the ideal average for me is 1 to 3 pulse to glide, at about 40 MPH average speed. 2200 in your car should be about 52 MPH. Thats for a 1.5 engine (not SI) and manual tranny (which I assume you have).

At above 50 MPH average try to find a draft. Vehicles with larger frontal areas than yours are best. It may be better to just draft than to try to P&G at higher speeds, try both methods to see which works best for you in your situation.

The same applies to the CRV except drafting would be much more effective.

Drafting for me is 3 highway stripes between me and the host vehicle on the Interstate at 65 MPH (about 125 feet). Lower speeds would be closer. At 45 MPH around here if you give the car in front of you more than 6 lengths, someone will always pull over in front of you and then slam on the brakes and turn right. I try to keep my minimum stopping distance between the host vehicle and my car. Closer may be more effective but it also becomes a lot more dangerous.

Every suggestion should be considered and adjusted to your specific desires and the traffic you have to deal with. I have driven 64 east from Richmond at 77 MPH, in bumper to bumper traffic with less than 5 cars lengths between any vehicle, for 60 miles, without anyone moving more than 200 yards ahead or behind anyone else. Thats pretty much the saturation point for a 2 lane (each way) Interstate at 65 MPH.

regards
gary
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Old 06-04-2008, 08:32 PM   #8
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question

I'm still trying to figure out P&G. Are you guys saying very light throttle in say, first, until I get close to 1.5 rpm's, then floor it until 2k, then shift, light throttle to 1.5, then floor it to 2k...etc.

I've been using light throttle always to 2k, then shift.

Quote:
Originally Posted by PaleMelanesian View Post
http://www.autospeed.com/cms/A_110216/article.html

High throttle, low rpm is best. Get the most efficient power out of the engine.

But... I'm finding that from a complete stop up to maybe 20mph, super light throttle ends up better. Then, when I'm closer to the desired speed, I switch into a heavy-throttle P&G routine.
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Old 06-04-2008, 09:35 PM   #9
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Hmmm... I'm not quite sure I follow.

From a stop, 1st quick to 2nd, up to 2000RPM, 3rd to 2000RPM, 4th to 2000RPM, coast.

That would be better than 1st/2nd/3rd then coast (higher RPMs), or 1st/2nd then coast (even higher RPMs)?

Would it help to take a counter videos while P&G'ding, with different scenarios to have experienced P&G'ers tell which looks and sounds liek the best P&G?


I usually P&G from 35 to 45, and I play the lights. If it turns orange and I'm close, accelerate, if I'm far, coast or even brake to get green before I have to stop.

I don't draft in city traffic because people's driving is erratic. I find P&G more effective, as I can coast 3-to-1 like said above, my commute is flat or slight inclines perfect for P&G with a low roll resistance car.
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Old 06-04-2008, 09:43 PM   #10
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For the fuel rate monitor, photos would be good, not just the taping of the injector, but overall what was done, the tapped wire needs to go back to the cabin.

Also the tap gives you:
-duty cycle
- engine RPMs

But you're missing speed to get MPG.

Therefore it'd be nice to tap another signal to get speed or tire rotations.

With that, we could do a cool ultra precise hypermiling analyzer.
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