How to accelerate in P&G mode?

[sonyhome]

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...

[theholycow]

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.

[sonyhome]

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).

[palemelanesian]

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.

[theholycow]

Originally Posted by sonyhome

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.

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.

Originally Posted by PaleMelanesian

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.

[cugir321]

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.

Originally Posted by PaleMelanesian

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.

[theholycow]

Originally Posted by cugir321

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.

You seem to be under the impression that P&G is practiced when you might otherwise be normally accelerating from a stop. That is not correct. P&G is used when you'd otherwise be cruising at a steady speed.

Heavy throttle and lower RPMs (to result in the same amount of acceleration as light throttle and higher RPMs) is more efficient than the way you accelerate. Of course that only works if you've got a manual or a very obedient tiptronic/manumatic/etc transmission.

Originally Posted by sonyhome

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.

Okay, I'll post some photos, but it's really really incredibly simple. Just run the wire to wherever your meter will be, and connect it to the meter's positive lead. Ground the negative lead to any ground (I use a power outlet) and enjoy.

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

The tap does not give you engine RPM, only fuel injector duty cycle.

But you're missing speed to get MPG.

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

Vehicle Speed Sensor (VSS) is what you need to tap for that, and I recently read (and surely posted) about a DIY MPG gauge that uses VSS and the fuel injector tap.

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

If we could run this all (VSS, FI tap, and tach) into a computer or log it, you're damn right. That's a good idea. That's definitely a project that merely requires adding FI tap as an auxilliary input to a ELM327 interface. I have no idea how that would be done, it might have to be done through a separate serial port and combined in software.

[theholycow]

Originally Posted by theholycow

Okay, I'll post some photos, but it's really really incredibly simple. Just run the wire to wherever your meter will be, and connect it to the meter's positive lead. Ground the negative lead to any ground (I use a power outlet) and enjoy.

I put up a couple photos. I thought I had more. Anyway, take a look at the DIY fuel flow meter thread again. It's linked in my sig. Let me know if I can take pictures of anything else for you.

[1993CivicVX]

Originally Posted by PaleMelanesian

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.

But there's no power at low RPMS! But who am I to argue with a gas getter guru? But I am finding that I'm using less gas with light acceleration and slightly higher RPMs than with full throttle low as possible RPMs. We both have lean burn engines, too, so what's true for you should be true for me, right?

[monroe74]

Originally Posted by 1993CivicVX

But there's no power at low RPMS!

This came up in another thread a few weeks ago. My VX pulls smoothly from 1000 rpm. Or even a bit less. Even in top gear, and even going up a moderate grade, and/or with one or more passengers. I think other VX owners have reported a similar experience. I think there might be something about your engine that is not providing proper power at low rpm. I realize you're still getting good results, but I think maybe you could do even better.

I think I suggested you check the timing. I don't recall if you mentioned doing that.