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daqcivic · 02-09-2009, 05:10 PM

So I am new to employing P&G as a dedicated FE technique, and I want to work out the finer points. I've read up quite a bit on what people have to say about it, so I think I've done enough research to get into a discussion about it.

As I understand it, the goal of P&G is to maximize FE by maximizing coasting distance/time (not sure which is better to think in terms of) and minimizing BSFC while DWL. (I understand min BSFC to be the RPM and load level at which the engine uses the least amount of fuel for the power being produced.) To put it another way, to get the best aggregate FE between coasting (EOC if possible) and pulsing (accelerating at the load and in the RPM range that will minimize BSFC, given the speed, power output, and gearing of the vehicle). It seems to have been very well demonstrated that this achieves significantly better FE than "egg-under-foot" acceleration and steady coasting for a given average speed and RPM, though the benefits are far greater for lower speed ranges.

The general wisdom seems to be that min BSFC (for the power output and speed/gearing of the vehicle) is achieved in low RPM ranges and with higher loads (however this is quantified, usually vacuum pressure, SCII readout, or pedal/throttle opening percentage). For my vehicle, a 92 Civic DX 5MT, since I cannot take advantage of a SCII and do not currently have a vacuum gauge installed, I have found PaleMelanesian's advice description of his P&G shifting and load scheme a helpful starting point, since he has a similar car, has refined his technique using a SCII, and describes his load in terms of throttle %. I have also found a helpful online speed/RPM in gear calculator for Hondas (Fatboy Raceworks » Graphical Transmission Gear Ratio Calculator), esp. since I have a different tire size than OEM. Here is my basic scheme (numbers are rounded) for for shift points and pulsing:

Gear beginning MPH/RPM ending MPH/RPM
1 0/idle 10/2000
2 10/1050 21/2150
3 21/1450 32/2200
4 32/1700 44/2300
5 44/1800 55/2200

This will no doubt be refined over time, but I think it's pretty close to ideal given real-world driving conditions. PaleMelanesian has also said he uses about a 50-60% load in lowest gears up to about 80% in higher gears (80% seems to be the consensus on the best general load to achieve min BSFC), so I am trying to emulate this as a starting point. (Forgive my lack of citation links, as I haven't figured out how to embed links yet.)

Aside from the way P&G goes against the grain of my intuitive sense, I have some questions and concerns about how to do it properly:

1. Should you keep the load steady through the whole speed/RPM range in a given gear, or should you gradually increase load through the range?

2. Should you peg the throttle at the given load level the split second the gear is engaged, or should you take a second or 2 to engage the gear smoothly and get up to the desired load? In the first case, the jerk of the engine would seem to waste fuel, but it would seem to be necessary to attain the desired load for the greatest percentage of the pulse time. In the second case, I figure smoother is usually better, but especially in shorter gears taking a second or more to smoothly get up to load means that ideal load is achieved for only a few seconds due to the rate of acceleration. In addition, in top gear there is very little acceleration at the low end of the RPM range regardless of the load level, so it would make sense not to use a higher load at such RPMs if no additional acceleration is achieved. My Civic takes forever to go from 45 to 50, but above that it gets much better.

3. Should you clutch-in and throttle-off the instant the high end of the speed range is achieved, or should you take 1/2 to 1 second to ease off the throttle before disengaging the clutch entirely? This is especially relevant to at least early to late 90s vehicles since lower emissions are achieved by having the computer let the revs hover a second after the throttle is let off suddenly. That extra second of revs could add up to a lot of wasted fuel, but if the throttle is decreased slowly in gear the effect would be reduced.

It is going to be a frustrating couple weeks before I can get through a full tank with P&G to see how well I'm doing with it, but I'd love some more discussion on the finer points so I can get the best start possible!

02-09-2009, 05:10 PM	#1 (permalink)
daqcivic 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	Finer points of P&G So I am new to employing P&G as a dedicated FE technique, and I want to work out the finer points. I've read up quite a bit on what people have to say about it, so I think I've done enough research to get into a discussion about it. As I understand it, the goal of P&G is to maximize FE by maximizing coasting distance/time (not sure which is better to think in terms of) and minimizing BSFC while DWL. (I understand min BSFC to be the RPM and load level at which the engine uses the least amount of fuel for the power being produced.) To put it another way, to get the best aggregate FE between coasting (EOC if possible) and pulsing (accelerating at the load and in the RPM range that will minimize BSFC, given the speed, power output, and gearing of the vehicle). It seems to have been very well demonstrated that this achieves significantly better FE than "egg-under-foot" acceleration and steady coasting for a given average speed and RPM, though the benefits are far greater for lower speed ranges. The general wisdom seems to be that min BSFC (for the power output and speed/gearing of the vehicle) is achieved in low RPM ranges and with higher loads (however this is quantified, usually vacuum pressure, SCII readout, or pedal/throttle opening percentage). For my vehicle, a 92 Civic DX 5MT, since I cannot take advantage of a SCII and do not currently have a vacuum gauge installed, I have found PaleMelanesian's advice description of his P&G shifting and load scheme a helpful starting point, since he has a similar car, has refined his technique using a SCII, and describes his load in terms of throttle %. I have also found a helpful online speed/RPM in gear calculator for Hondas (Fatboy Raceworks » Graphical Transmission Gear Ratio Calculator), esp. since I have a different tire size than OEM. Here is my basic scheme (numbers are rounded) for for shift points and pulsing: Gear beginning MPH/RPM ending MPH/RPM 1 0/idle 10/2000 2 10/1050 21/2150 3 21/1450 32/2200 4 32/1700 44/2300 5 44/1800 55/2200 This will no doubt be refined over time, but I think it's pretty close to ideal given real-world driving conditions. PaleMelanesian has also said he uses about a 50-60% load in lowest gears up to about 80% in higher gears (80% seems to be the consensus on the best general load to achieve min BSFC), so I am trying to emulate this as a starting point. (Forgive my lack of citation links, as I haven't figured out how to embed links yet.) Aside from the way P&G goes against the grain of my intuitive sense, I have some questions and concerns about how to do it properly: 1. Should you keep the load steady through the whole speed/RPM range in a given gear, or should you gradually increase load through the range? 2. Should you peg the throttle at the given load level the split second the gear is engaged, or should you take a second or 2 to engage the gear smoothly and get up to the desired load? In the first case, the jerk of the engine would seem to waste fuel, but it would seem to be necessary to attain the desired load for the greatest percentage of the pulse time. In the second case, I figure smoother is usually better, but especially in shorter gears taking a second or more to smoothly get up to load means that ideal load is achieved for only a few seconds due to the rate of acceleration. In addition, in top gear there is very little acceleration at the low end of the RPM range regardless of the load level, so it would make sense not to use a higher load at such RPMs if no additional acceleration is achieved. My Civic takes forever to go from 45 to 50, but above that it gets much better. 3. Should you clutch-in and throttle-off the instant the high end of the speed range is achieved, or should you take 1/2 to 1 second to ease off the throttle before disengaging the clutch entirely? This is especially relevant to at least early to late 90s vehicles since lower emissions are achieved by having the computer let the revs hover a second after the throttle is let off suddenly. That extra second of revs could add up to a lot of wasted fuel, but if the throttle is decreased slowly in gear the effect would be reduced. It is going to be a frustrating couple weeks before I can get through a full tank with P&G to see how well I'm doing with it, but I'd love some more discussion on the finer points so I can get the best start possible! Last edited by daqcivic; 02-09-2009 at 05:23 PM..