EcoModder Forum Finer points of P&G

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TacoModder

Join Date: Nov 2008
Location: San Diego, CA
Posts: 108

rik's prerunner - '03 Toyota Tacoma Prerunner Double Cab TRD 4A
90 day: 29.68 mpg (US)
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If you wanna get right to the "finer points" and aren't afraid of some high school math, take a look at this party-killer I posted a few months back.

The gist is that if you have a gauge that'll give you your instantaneous GPH, you can easily calculate your break-even pulse-to-glide ratio for different scenarios.

Quote:
 For those who want to see how to compute this: * P&G Gas Used = PulseRate x PulseTime + GlideRate x GlideTime * DWL Gas Used = DWLrate x DWLtime Plug in your averages: You'll need to choose a cycle time to compare, ex. 5 second pulse and 10 second glide = 15 total seconds. * P&G gas used = 4.0 gph x 5 sec + .4 gph x 10 sec = 20 + 4 = 24 * DWL Gas Used = 1.3 gph x 15 sec = 19.5 So you can see that using a 5 to 10 pulse-to-glide ratio (or 1 to 2) is not fuel-efficient for me.
In the final analysis, all you're really aiming for is to use less gas in a certain amount of time than you would cruising. Since every car is different, the best approach IMO is to get a gauge and do the observation/calculation. Good luck!

 02-09-2009, 07:52 PM #3 (permalink) EcoModding Lurker   Join Date: Nov 2008 Location: Portland, OR Posts: 53 Daq Civic - '92 Honda Civic DX sedan 90 day: 42.54 mpg (US) The Hardbody - '91 Nissan D21 (pickup) The Hardbody - '91 Nissan D21 (pickup) Thanks: 1 Thanked 7 Times in 5 Posts Thanks, akashic, I had actually read that post earlier and found it helpful in recognizing how simple it is in principle to compare a P&G scheme to DWL. Some way of measuring instantaneous fuel consumption would be wonderful, but I am not aware of a way to do that with an OBD-I vehicle. The next best thing seems to be a vacuum gauge, and I'm definitely considering getting one, but there isn't necessarily a precise relationship between manifold pressure fuel consumption. The "finer points" I am most interested at this point are the numbered items in my post, that is, whether it is better to gradually build load during acceleration through a gear or to keep load steady the whole time, and whether it is better to give priority to smoothness or quickness during shifting, P>G, and G>P transitions. What I'm trying to get at is, given that you've learned the ideal acceleration and P&G schemes for best FE, how do you refine your technique further? Anyone out there with a 92-95 Civic DX/LX who's got P&G nailed?
TacoModder

Join Date: Nov 2008
Location: San Diego, CA
Posts: 108

rik's prerunner - '03 Toyota Tacoma Prerunner Double Cab TRD 4A
90 day: 29.68 mpg (US)
Thanks: 0
Thanked 2 Times in 1 Post
Quote:
 Originally Posted by daqcivic Some way of measuring instantaneous fuel consumption would be wonderful, but I am not aware of a way to do that with an OBD-I vehicle. The next best thing seems to be a vacuum gauge, and I'm definitely considering getting one, but there isn't necessarily a precise relationship between manifold pressure fuel consumption. The "finer points" I am most interested at this point are the numbered items in my post, that is, whether it is better to gradually build load during acceleration through a gear or to keep load steady the whole time, and whether it is better to give priority to smoothness or quickness during shifting, P>G, and G>P transitions. What I'm trying to get at is, given that you've learned the ideal acceleration and P&G schemes for best FE, how do you refine your technique further? Anyone out there with a 92-95 Civic DX/LX who's got P&G nailed?
If you're interested splitting hairs, you need to be able to see them. The mpguino is what you want. It's for pre-OBDii cars, and it's all over this site. Without one, you're like a competitive sprinter without a stopwatch or a standardized track. You need the instantaneous feedback. Right now, even if your tank miles are going up since you started P&G, you can't conclusively know that it was the P&G that helped. One reputable ultra-hypermiling member with a Civic, after installing his mpguino, reported that he got WORSE mpgs with P&G. You really need the feedback to sort any of this out.

 02-09-2009, 09:11 PM #5 (permalink) EcoModding Lurker   Join Date: Nov 2008 Location: Portland, OR Posts: 53 Daq Civic - '92 Honda Civic DX sedan 90 day: 42.54 mpg (US) The Hardbody - '91 Nissan D21 (pickup) The Hardbody - '91 Nissan D21 (pickup) Thanks: 1 Thanked 7 Times in 5 Posts I get what you're saying, I'm not sure I can figure out the mpguino install and programming. I don't even know how to read electronic schematics or tap into a wire.
 02-09-2009, 11:31 PM #6 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 22,275 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 52.07 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 61.98 mpg (US) Fancy Metro - '14 Mitsubishi Mirage top spec 90 day: 58.72 mpg (US) Even Fancier Metro - '14 Mitsubishi Mirage top spec 90 day: 70.75 mpg (US) Thanks: 3,811 Thanked 6,690 Times in 3,468 Posts daqcivic: if I'm not mistaken, you can now buy a pre-assembled MPGuino programmed with the latest code. You'd still need to install it, but I suspect you could also get help with that from the members in the MPGuino subforum. And to split hairs as precisely as you want, it seems like you'll need a BSFC map for your engine. __________________ Honda mods: Ecomodding my \$800 Honda Fit 5-speed beater Mitsu mods: Oops, I did it again! Bought another cheap, 3-cylinder Mirage. Mods in progress... Ecodriving test: Manual vs. automatic transmission MPG showdown EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget
 02-10-2009, 11:31 AM #7 (permalink) Hypermiler     Join Date: Dec 2007 Location: Texas Posts: 2,320 PaleCivic (retired) - '96 Honda Civic DX Sedan 90 day: 69.2 mpg (US) PaleFit - '09 Honda Fit Sport Team HondaWagons 90 day: 44.06 mpg (US) Thanks: 611 Thanked 428 Times in 280 Posts You rang? What I'm talking about is lower THROTTLE in the low gears and at low rpm, and higher throttle at higher rpm. At low rpm, it takes less to fill the cylinders, since the valves are open longer. (lower rpm = longer time for each cycle) Watching the MAP and LOD gauges on the SG, I aim for ~50% throttle, building up to 80% as the rpms climb. If you're in the gear for more than a few seconds, definitely taper it (heavier) as you gain speed. Gears: Your shifting scheme looks pretty good. You can go a little lower on the rpm, shifting a little sooner. If it growls/rumbles a bit, that's fine. As long as it can gain speed it's ok. I hardly use 1st gear. On a downhill start, I don't - I go straight to 2nd. On flat/uphill starts, I only use it to get rolling, and shift to 2nd about as soon as it's fully engaged. (3mph or so?) The transitions between pulse and glide are a small part of the whole, but when you do them so much, I guess it can make a difference. If you can minimize the number of P&G cycles, they matter less. I finish my pulse, clutch in, and 1/2 sec later key off, right as the revs reach the lowest point. Even the Scangauge can't measure at a fine enough resolution to show the best method here. My reasoning is that this way I have the shortest time in the key-off position, since the low-rpm engine dies that much sooner. For the pulse, I do recommend getting a vacuum gauge. I've seen that ~80% load on the Scangauge is about 12psi MAP, so you can aim for that. If your rpm is low enough, shifting with both quickness and smoothness is really really easy. As for BSFC charts, the colorful one in this article seems to be good enough for my purposes. Just aim for the red zone. Article: Browser Warning Overall, I find that getting the very best pulse less important than getting the best glide. You can do a 1:1 pulse to glide ratio, with a light pulse, or you can do a heavy pulse with a glide 3x as long. Both will give you similar results. Gauge the terrain, traffic, and other conditions to get the best glide you can. If that means pulsing on an uphill, do that. You can then coast up and over the peak and down the other side. You have to fight the urge to "do something", and just wait it out. Ok, rambling done. Hopefully some is useful. __________________ 11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
EcoModding Lurker

Join Date: Nov 2008
Location: Portland, OR
Posts: 53

Daq Civic - '92 Honda Civic DX sedan
90 day: 42.54 mpg (US)

The Hardbody - '91 Nissan D21 (pickup)

The Hardbody - '91 Nissan D21 (pickup)
Thanks: 1
Thanked 7 Times in 5 Posts
Quote:
 What I'm talking about is lower THROTTLE in the low gears and at low rpm, and higher throttle at higher rpm. At low rpm, it takes less to fill the cylinders, since the valves are open longer.
That makes perfect sense. I was a little confused from an earlier post where you listed a throttle % according to gear, not RPM; but of course, the engine doesn't care what gear it's in or even really what speed the vehicle is at, just what RPM it's at and what load is being demanded based on the throttle. So if there is enough time spend in gear I should begin initially with about 50% and increase up to about 80%. However, for my car's gearing, since RPMs at initial engagement speed in 2nd and 3rd are below the rule-of-thumb optimal BSFC range of about 1500-2200RPM, (around 800-1000 in 2nd and 1200-1400 in 3rd), it would seem best to begin in these gears with less than 50% throttle, until the RPM gets up to at least 1500.

Quote:
 Your shifting scheme looks pretty good. You can go a little lower on the rpm, shifting a little sooner. If it growls/rumbles a bit, that's fine. As long as it can gain speed it's ok.
This is something I definitely need a gauge for. Going lower seems like it wastes fuel because I end up spending a couple more seconds at those lower RPMs with almost no acceleration. Then again, Lower shift points mean fewer overall cycles, so it would take some pretty precise testing to with good instrumentation to figure out where the optimal point is. On the upside, a few hundred RPMs difference in shifting points is probably going to have a minuscule effect on FE if the load is managed smartly.

Quote:
 I hardly use 1st gear. On a downhill start, I don't - I go straight to 2nd. On flat/uphill starts, I only use it to get rolling, and shift to 2nd about as soon as it's fully engaged. (3mph or so?)
I hear most people saying this, and I don't necessarily disagree (as if I could provide any solid evidence to the contrary), but it does seem to contradict the BSFC logic of using the engine in its most efficient range because 2nd gear is used for several hundred RPMs before 1500. I'm going to accept the prevailing wisdom of this for now, though I hate lugging the engine.

Quote:
 Overall, I find that getting the very best pulse less important than getting the best glide. You can do a 1:1 pulse to glide ratio, with a light pulse, or you can do a heavy pulse with a glide 3x as long. Both will give you similar results. . . . get the best glide you can.
This is really helpful! I had gotten good at maximizing coasting using very slow, light load acceleration, but it is quite a bit different and more difficult to time things (esp. in rush hour city traffic with hills and such) using heavy load acceleration. But if I know I can freely adapt the P&G ratio to fit the circumstances to get the most gliding I will probably do a lot better than trying to stick to a rigid pulse scheme.

It's definitely starting to sink in that I can't really refine things much and know if it's helping unless I get some instrumentation. Thanks MetroMPG for the advice on mpguino, I imagine I could find out where those few leads are by looking it up in a manual.

And thanks to all for your advice and willingness to help a clueless beginner!

 02-10-2009, 01:24 PM #9 (permalink) Hypermiler     Join Date: Dec 2007 Location: Texas Posts: 2,320 PaleCivic (retired) - '96 Honda Civic DX Sedan 90 day: 69.2 mpg (US) PaleFit - '09 Honda Fit Sport Team HondaWagons 90 day: 44.06 mpg (US) Thanks: 611 Thanked 428 Times in 280 Posts The uphill pulse / downhill coast thing helps in traffic. You keep a fairly constant speed, building potential energy instead of kinetic during the pulse. Short of getting some instrumentation, you need a reliable/consistent fillup routine. Same station, same pump, same time of day, etc. __________________ 11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
 02-10-2009, 01:50 PM #10 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 22,275 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 52.07 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 61.98 mpg (US) Fancy Metro - '14 Mitsubishi Mirage top spec 90 day: 58.72 mpg (US) Even Fancier Metro - '14 Mitsubishi Mirage top spec 90 day: 70.75 mpg (US) Thanks: 3,811 Thanked 6,690 Times in 3,468 Posts Also, since you willingly label yourself a "clueless beginner", please take the time to develop your technique in a quiet environment before unleashing it in traffic! (And I'll assume you're aware of what happens to your power steering and vacuum assisted brakes when driving with the engine off.) Driving safely takes enough effort on its own. Throwing a P&G learning curve into the mix can divert a lot of attention from other tasks. Later, when it becomes an "automatic" habit, that's less of an issue. __________________ Honda mods: Ecomodding my \$800 Honda Fit 5-speed beater Mitsu mods: Oops, I did it again! Bought another cheap, 3-cylinder Mirage. Mods in progress... Ecodriving test: Manual vs. automatic transmission MPG showdown EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget

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