P&G Questions

[dosco]

Is there a sticky here that:

1. Explains, in detail, how to drive using P&G techniques,

-or-

2. Has links to sites that explain P&G?

Yesterday, after reading a site (IIRC linked by PaleMelanesian) about BSFC, I can understand the fundamentals behind P&G. Question is, it seems like I'm accelerating "violently" (relatively speaking) ... not sure if I'm doing it right...

[PaleMelanesian]

Look in the articles section at CleanMPG. Or look it up on MetroMPG. Both have explanations of how it works. Yes, the higher acceleration is counterintuitive at first, but it works. If you keep the rpm low enough, though, you're not going to be all that violent.

[dosco]

Look in the articles section at CleanMPG. Or look it up on MetroMPG. Both have explanations of how it works. Yes, the higher acceleration is counterintuitive at first, but it works. If you keep the rpm low enough, though, you're not going to be all that violent.

I read some stuff on both sites. The CleanMPG info seemed mostly about hybrids (admittedly I didn't dig real hard or deep) and the MetroMPG stuff lacked detail.

I guess my question is this: do I focus on my speedometer or on throttle angle and tach?

The reason I ask is due to the issue of the BHP SFC charts linked on the other site (that I think you provided). If the optimal SFC is at a particular load and RPM, should I try and hit that or simply focus on the car's speed? I've been focusing on RPM and throttle angle, and as such the accelerations seem rather brisk.

I realize one answer will be "buy a ScanGauge II." I will eventually, but in the meantime, can I P&G and improve FE?

[PaleMelanesian]

I highly recommend the scangauge. In the mean time:
Manual trans:
Keep the rpm below about 2,200. Use 1/2 to 3/4 throttle until you get up to your top speed. Let's say that's 55. Then pop into neutral and coast down to 45 or 40. Back into gear (probably top ear, but whatever will give you 2,000ish rpm) and pulse up again. Up-down-up-down. Sometimes I start the pulse in 4th and shift into 5th partway through.

Automatic - you'll have to use less throttle, to avoid a transmission kickdown. That's a killer on fuel economy.

[dosco]

Manual trans:
Keep the rpm below about 2,200. Use 1/2 to 3/4 throttle until you get up to your top speed. Let's say that's 55. Then pop into neutral and coast down to 45 or 40. Back into gear (probably top ear, but whatever will give you 2,000ish rpm) and pulse up again. Up-down-up-down. Sometimes I start the pulse in 4th and shift into 5th partway through.

Automatic - you'll have to use less throttle, to avoid a transmission kickdown. That's a killer on fuel economy.

Don't have a manual trans.

OK. I've been trying to emulate what you've described by using "1," "2," and the OD button. Will continue to do so and track MPG.

[PaleMelanesian]

There's no need to use the 1 and 2. You want to be out of those gears as soon as you can, not hold it in low gear. I'd leave in Drive and work at keeping the rpm low. Once you know your car's shift points, let up when you reach that speed, let it shift, then get back on it, only now you're in a higher gear / lower rpm.

[dosco]

There's no need to use the 1 and 2. You want to be out of those gears as soon as you can, not hold it in low gear.

Indeed. What I've been doing is at lower speeds, to use the "1" or "2" to get to an appropriate throttle angle/RPM, followed by a shift to "N." Of course, I don't do this at higher speeds.

I'd leave in Drive and work at keeping the rpm low.

I was under the impression, from the BHP SFC graphs, that too low of an RPM is bad (of course is worse with low loads), and that a target RPM was desirable...? No?

Gonna have to get that damned scangauge....

[PaleMelanesian]

I think you're over thinking the low speed part of it. Just let the auto do its thing up to 20-25 mph, with a gentle throttle. Then work on P&G. Also, with an automatic, DWL is a bigger help. Driving with Load - lose speed on the uphills and gain it on the downhills.

[dosco]

I think you're over thinking the low speed part of it.

Probably. Heh.

Also, with an automatic, DWL is a bigger help. Driving with Load - lose speed on the uphills and gain it on the downhills.

Got it.

[monroe74]

I've only recently started doing P&G, so I'm no expert. But I think I've arrived at a specific way of thinking about it that makes the technique fairly easy for me to understand and implement. I haven't seen anyone else explain it exactly this way, although my technique is 100% derived from reading the material that others have kindly provided.

The basic underlying idea is that a gas engine is most efficient with a large throttle opening. Theoretically, the most efficient setting is when the throttle is completely open (otherwise you get what are called pumping losses, where the engine is doing extra work to overcome the vacuum created by the throttle). But as a practical matter, most (all?) EFI cars open the injectors completely upon full throttle, and this wastes gas (it dumps in more gas than the engine can use). So in real terms, the most efficient throttle setting is perhaps, say, 70% open.

So what I do is I try to adopt the idea that my throttle is a binary switch, with only two acceptable settings: off (completely closed), and 70% open. Let's just call it OFF and ON. That's the key concept, for me. Then I adjust my driving to take this into account. I strive to avoid any throttle setting other than those two.

So let's say I'm driving along a typical suburban road, at about 40 mph. Let's say the speed limit is 45 mph. The traffic is light-to-moderate. I'm in top gear, with the throttle 70% open (ON), and the road is flat. This means I'm accelerating. So I let my speed get to, say, 50 mph. This brings me pretty close to the car ahead of me. So then I drop into neutral (I could also turn the motor off, but the important thing is to at least drop in neutral). And now of course the throttle is OFF (if I didn't turn off the motor, some gas is being used to keep the motor idling, but to keep things simple let's still call this 'OFF'). Now I'm coasting. I let it coast down to, say, 35 mph. Then I shift back into top gear and I turn the throttle back ON, that is, I move the throttle to the other acceptable setting (70% open.) Now I'm accelerating again, from 35 mph. When I reach, say, 50 mph, I drop into neutral again, and turn the throttle OFF. Rinse and repeat.

If conditions are right, and if I'm skillful, I can avoid annoying the driver behind me and the driver ahead of me. At the moment I hit 50 mph and am about to start coasting, I am as close the car in front of me as I am willing to safely go. At the other end of the cycle, when I am done coasting and am about to start accelerating again, I have dropped back and gotten close to the car behind me. But not too close. If traffic isn't very heavy, and there's a reasonable space between those two cars, I'm simply using that space fully, without getting too close to either of them.

Another important idea is keeping revs as low as possible, which means upshifting early (about 1200-1600 rpm, on my car). But when I'm doing a nice long P&G routine, doing (let's say) 35-50 mph over a long distance, the only gears I'm using are 5 and neutral. And I'm not paying attention to the tach. I'm mostly focusing on the two acceptable throttle positions (OFF and ON), and I'm paying attention to the speedo, and my position relative to my neighbors (in front of me and behind me).

"do I focus on my speedometer or on throttle angle and tach?"

As I explained, I'm paying a lot of attention to throttle angle, and also to the speedo. But I'm paying no attention to the tach. This assumes I'm going fast enough (say, over 25 mph) where the only two gears I need are neutral and 5.

Of course if I approach a grade, things change. I might have to use 4, or 3. But I still want to follow the rule about ideal throttle opening (either closed or 70% open), regardless of what gear I'm in. If I'm at 70% throttle in 3 or 4 and getting too close to the car in front of me, that means I should have shifted to 5, or I should be coasting ('gliding'). In fact, I can apply these simple rules to pretty much any driving situation. If throttle ON is giving me too much speed, that means I should be shifting up. And if I'm already in top gear, and I have too much speed, that means I should be coasting.

Conversely, anytime the throttle is OFF (i.e., I'm coasting), and I find I don't have enough speed (to avoid annoying the driver behind me, let's say), that means it's time to turn the throttle ON. And in the highest possible gear.

There's one more idea that's helpful. It has to do with the fact that coasting ('gliding') really comes in three flavors, as follows:

A) coasting in neutral; the engine is idling
B) coasting in neutral; the engine is off ('engine-off coasting,' or EOC)
C) coasting in gear; engine braking is slowing the car down

The interesting thing is that C uses less gas than A. Why? Because when I'm coasting in gear (i.e., using engine braking), then the injectors are completely off. If I'm coasting in neutral (with the engine on, throttle closed), the injectors aren't completely off; they have to provide gas to keep the engine idling. So sometimes it's better to use C instead of A. But this would be the case only when my intention is not to maximize coasting distance.

This concept becomes relevant in the following situation (or in similar situations). I'm cresting a hill. There's a long, moderate downgrade ahead, and then a stop sign. I know I will have to stop, at the bottom of the hill. I know I don't need throttle ON to get down the hill. Gravity and momentum is more than enough to get me there. B would be ideal, but let's imagine I prefer to avoid that, for whatever reason. I still have two choices: I could use A, and then use my brakes at the bottom. Or I could use C, and avoid A, and then perhaps not need to use my brakes. This latter technique saves gas. Why? Because C is more efficient than A.

I could also just have the engine off while I glide down the hill (B). That's fine too. The key point is to realize that in this particular situation I can save a little gas by using C instead of A (and C should consume no more gas than B).

Note this related paradox: an engine at 3000 RPM can be using less gas than the same engine idling. How is that possible? When the engine at 3000 RPM has a closed throttle, and is being driven by the car's momentum (i.e., it's in engine-braking mode).

"I was under the impression, from the BHP SFC graphs, that too low of an RPM is bad"

No, I think this is a bad misunderstanding on your part. Lower RPM is always better, assuming your engine isn't pinging. And assuming your engine is generating enough power to do what's needed (e.g., push your loaded car up a grade at a speed sufficient to avoid annoying the driver behind you). If you can't get up the grade, downshift and get higher RPM. But always seek low RPM, whenever possible.

There are many folks here who know a lot more than me, so I hope they chime in with any corrections. Those folks include Pale. I've learned a lot from his posts. I think what I've said is congruent with what he's saying in this thread.

[RoadWarrior]

Probably in an auto your BSFC has to increase more than 10% to get over the difference between having the TC locked up and not, as it will most likely unlock under anything other than light acceleration. Also you probably need to stay between 2000 and 3000 in an auto, depending what your TC stall speed is, low RPM in an auto is like trying to paddle a canoe up a fast moving shallow stream, vs punting it with a stick.

[Hateful]

On my way home from work I have to start at the bottom of a steep hill,flattens out,back down the other side and turn to the right. I accelerate briskly enough to reach 45mph and the top, continue accelerating on about half the flat part,go into neutral and coast halfway down the other side. Then I put it back into drive and let the car low to at least 37mph.Once I've made it around the turn without flipping over I accelerate again.
Putting the car back into drive slows the car enough not to flip and turns the motor so I've already got my RPMs up for the next hill.
you can go slow and still be reckless

[PaleMelanesian]

That's a pretty good explanation there, Monroe.

Here's more discussion: http://www.gassavers.org/showthread.php?t=4455

low RPM in an auto is like trying to paddle a canoe up a fast moving shallow stream
It sure is! It's a challenge, to put it lightly.

[dosco]

"I was under the impression, from the BHP SFC graphs, that too low of an RPM is bad"

No, I think this is a bad misunderstanding on your part. Lower RPM is always better, assuming your engine isn't pinging.

Here's the link that Pale provided: http://www.autospeed.com/cms/A_110216/article.html

Look at the graphs.

After re-looking, I guess it depends on what chart you look at - the 3rd chart reflects what you are saying - low RPM (below 3,000) is good, regardless of throttle angle.

What I'm thinking about is the 2nd graph that shows SFC vs. RPM, and has 3 curves for engine load. It's pretty clear from that graph that the most fuel efficient operating condition, regardless of load, is between 3,000 and 3,500 RPM.

Are you sure you are using 70% throttle? That's a lot. If I'm using 1/2 throttle, the acceleration is very brisk, and I'm concerned about using "full" (or close to full) for the sake of FE. Maybe I'm worrying too much.

Anyways, as Pale said earlier, I'm probably overthinking things and need a ScanGauge II.

[PaleMelanesian]

According to the Scangauge, I'm using 80% or higher throttle. My main target is to keep it just under the point where it adds extra fuel. You can see that on the SG by watching when it goes into Open Loop mode.

From my experience, the 4th, 5th & 6th graphs in the article match best with my engine. Yours may be different. You'll have to experiment and see.

[monroe74]

disco: "Here's the link that Pale provided"

Thanks for reminding me where to find that article. I think it's very helpful.

"Are you sure you are using 70% throttle?"

I think there's a magic number, and I think 70 is probably about right, but I don't know if 70 is exactly right. I don't mean to imply that it is.

The issue is that at full throttle, the computer opens the injectors 100%. I think that's what's called open-loop mode. In the absence of a SG or similar instrument (like a DMM), it's hard to know exactly when this starts happening.

Open-loop mode wastes fuel. So the most efficient setting is somewhere slightly short of full throttle. And the right answer probably varies for different cars. What you want is the maximum throttle opening (because this reduces vacuum and therefore reduces pumping losses), just short of sending the ECU into open-loop mode.

"It's pretty clear from that graph that the most fuel efficient operating condition, regardless of load, is between 3,000 and 3,500 RPM."

I think you're misinterpreting the graph (http://www.autospeed.com/cms/gallery/article.html?slideshow=0&a=110216&i=6). The graph doesn't say that 3200 RPM is highly efficient "regardless of load." The graph says that at any given load, 2800-3200 RPM is highly efficient. Here's the key to understanding the graph: "load" basically means "throttle opening."

You are noticing, correctly, that given a load of 100%, that the engine is most efficient at 3200 RPM. This simply means that if the engine is running full throttle at 3200 RPM, it is more efficient than when it is running full throttle at, say, 1000 RPM. Fair enough. Here's what that means in terms of driving.

I'm climbing a steep hill. I'm in top gear. I have the throttle wide-open (for the moment, let's set aside the open-loop issue). The engine is at 1000 RPM. My speed is probably about 20 MPH. The speed is constant; i.e., I'm producing exactly enough power to fight gravity and travel up the hill.

Now imagine that I downshift to 3rd, or 2nd. RPM is now 3200. The throttle is still wide-open. Speed is still 20 MPH, and is still constant. I'm still producing exactly enough power to fight gravity and travel up the hill. But I'm not accelerating, because the hill is very steep.

The graph shows that in this circumstance, I am indeed better off in the lower gear. In other words, when heavy throttle in a low gear is not enough to raise my speed (assuming I am not already at the redline), maybe that means the hill is so steep (and/or the trailer is so heavy, and/or the headwind is so great) that I actually belong in that lower gear, and shouldn't upshift.

But this is an unusual circumstance. For almost all modern cars (even with low-power engines), if we assume a flat road and a vehicle carrying only one or two people, then full throttle (or 70%, if we want to take the open-loop issue into account) is enough to produce acceleration, even in top gear. Unless we're already at a high speed (like 90 mph), where air resistance is providing the equivalent of a steep grade.

In other words, if we're using the throttle to keep the engine at high efficiency, that probably means we're accelerating. That's the essence of P&G: acceleration, alternated with coasting.

Back to the graph. Yes, given a fully-open throttle, 3200 RPM is more efficient than 1000 RPM. But our cars do not stay at 1000 RPM, if the throttle is fully-open. Even in top gear. They accelerate. Unless you're climbing a grade, and then it indeed makes sense to downshift. But the important thing is to keep the throttle fully open (70%), except for when you're coasting. If I'm climbing a hill in 3rd gear, with full throttle, and this is not producing acceleration, then you're right, I probably shouldn't be in a higher gear, even if that would let me lower the revs.

"If I'm using 1/2 throttle, the acceleration is very brisk"

Life is much more complicated with an automatic. It's probably brisk because your tranny decided to downshift. That's what an auto trans usually does, when you give it a large throttle opening. A stick is much better, in this regard, because it lets you choose a large throttle opening without downshifting.

Theoretically, we want full throttle 100% of the time, except when we're coasting. I say 'theoretically' because we have to back off just enough to avoid open-loop mode. And with an automatic, you also have to back off just enough to avoid unwanted downshifting.

[dosco]

Thanks for reminding me where to find that article. I think it's very helpful.

It is. I found another link to a very long paper that expounded on the graphs at the speed site. I'll dredge it up again, if interested ... but it basically says the same thing as the speed article.

The graph doesn't say that 3200 RPM is highly efficient "regardless of load."

Perhaps my choice of words wasn't so great, but the graph clearly shows that at the various load conditions (25%, 75%, 100%), the most efficient rev range is 3,000 to 3,500 or so.

I agree with you, though, so no argument.

For almost all modern cars (even with low-power engines), if we assume a flat road and a vehicle carrying only one or two people, then full throttle (or 70%, if we want to take the open-loop issue into account) is enough to produce acceleration, even in top gear.

Indeed. The very essence of P&G driving. I think we're in agreement.

Life is much more complicated with an automatic. It's probably brisk because your tranny decided to downshift.

I used to drive a stick, and am very conscious of what the auto trans is doing - thus my focus on both RPM and throttle angle.

I think the "brisk" part is b/c I've been driving with small throttle openings and low accelerations for so long that it seems very odd to be "flooring" it (not literally) and accelerating briskly.

Theoretically, we want full throttle 100% of the time, except when we're coasting.

This is where a CVT for a gasoline+spark engine comes into play... ...

[RoadWarrior]

This is where a CVT for a gasoline+spark engine comes into play... ...

Or should... unlike the shining example of the dodge caliber :rolleyes:

'95 Neon using venerable torqueflite hydraulic 3 speed transmission. 26mpg combined.
'05 porked out final year Neon, with electronic 4 speed ultradrive, 25mpg combined
'08 Caliber, CVT transmission, 24mpg combined.

On that evidence I should be grateful I've got the old 3 speed torqueflite technology auto in my minivan, and not go wishing for CVTs or a 4th gear.

[dosco]

On that evidence I should be grateful I've got the old 3 speed torqueflite technology auto in my minivan, and not go wishing for CVTs or a 4th gear.

Oh, I don't wish for one either. It reminds me of the SCCA F400 (?) class that used snowmobile CVTs. I can't say that I cared for those things at all.

[monroe74]

dosco: "I found another link to a very long paper"

If you found that link on this site, I think maybe I saw it too. I vaguely remember some other similar paper, that I found via a link cited in this forum. If you found the link on another site, I think I'd like to see it, if you have it handy.

"the graph clearly shows that at the various load conditions (25%, 75%, 100%), the most efficient rev range is 3,000 to 3,500 or so"

Yes, the graph shows that high revs (about 3000) are more efficient than lower revs. But this is easily misunderstood, because the graph also shows that at any given engine speed, 100% throttle is always more efficient than 25% throttle. Following the graph, we would seek to be at 3200 RPM and 100% throttle. Trouble is, even a low-powered car is typically too powerful to maintain this state, unless it's climbing a steep hill.

The essential message of the graph is this: the engine is most efficient when the throttle is fully open. It's very counter-intuitive, but the key to saving gas is to open the throttle! (Almost fully, except for the issues I cited, about open-loop and about how an auto trans likes to downshift.) And then coast.

"I think the 'brisk' part is b/c I've been driving with small throttle openings and low accelerations for so long that it seems very odd to be 'flooring' it (not literally) and accelerating briskly."

Good point. I see what you mean. P&G is a challenge because it violates our old habits and expectations. It also has to be done skillfully, and with planning. I'm wasting gas if I accelerate and then have to turn that energy into brake heat, instead of coasting distance.

"This is where a CVT for a gasoline+spark engine comes into play"

Exactly. Grasping those BSFC charts makes it easier for me to understand why CVT is important. But I think we can see that it's possible to get good results without one, if the driver understands the principles we've been discussing.

[monroe74]

Pale, thanks for the compliment. I greatly respect your opinion. A lot of what I've learned is from you. I've read 100% of your comments. Your comments and your gaslog are a big part of what convinced me that I should try really hard to thoroughly grasp the theory and practice of P&G.

I've looked very closely at many gaslogs. There are two things I find very distinctive about yours. The first thing is that you're very much (95%) above EPA. This is virtually unheard of. Out of almost 400 vehicles currently in the garage, only 3 or 4 currently exceed you in this measure. And none by very much. This is especially impressive since your car is almost 100% stock. The four vehicles ahead of you all have fairly extensive mods, most including aero mods (beyond just a simple grill block, which is your only aero mod).

The other thing I find distinctive about your gaslog is that it shows a slow, steady improvement. Obviously FE is a combination of car factors (e.g., tire pressure), environmental factors (e.g., ambient temperature) and driver factors (e.g., skillful application of techniques like P&G). It looks to me like your steady improvements are mostly based on driver factors. I think the nature of P&G (and related techniques, like EOC) is that it can be done in a moderately skillful way, or in an exceptionally skillful way. It lends itself to constant refinement. So you seem to be on a learning curve, and perhaps not yet done refining your technique (but nevertheless way ahead of the rest of us).

Anyway, I had a lot of trouble grasping P&G until I saw those BSFC articles. They're very technical, and my previous posts are long, so I'll put the key insight in a nutshell:

There's one throttle setting (probably about 70%) that's more efficient than any other. ADJUST YOUR DRIVING SO YOU'RE NEVER USING ANY OTHER THROTTLE SETTING (except, of course, when you're coasting, and your foot is off the pedal). You should also be using the highest possible gear, most of the time. It also helps to understand the three kinds of coasting.

(Getting all this right with an automatic is a special challenge.)

It seems to me that this is what P&G is really all about: always use 70% throttle, or no throttle at all.

With P&G, you're operating the engine at high efficiency (70% throttle, during the pulse phase). This creates more power than you really need, so the car accelerates. The extra power is being converted into kinetic energy (momentum in the car). Then you coast, and rely on that kinetic energy. Gas consumption is very low (or even zero) while you're coasting. You save gas because you approach the following ideal: the engine is either operating at top efficiency, or not operating at all. This is much better than a steady speed, at partial throttle, where a lot of energy is wasted on pumping losses.

It's OK if you (i.e., non-technical readers) don't understand the concept of pumping losses. Just apply this simple rule: the only acceptable throttle setting is 70%.

[monroe74]

What I find interesting about P&G is that it requires me to unlearn years of driving habits. I was always taught to strive for moderate throttle openings ('drive like there's an egg under your foot'). WRONG.

Likewise for those old vacuum gauges which embodied the idea that high vacuum meant high FE. Also wrong. The idea only persisted because high vacuum often meant 'going really slowly.'

Those old vacuum gauges were sometimes called an 'economy meter' or a 'motor minder.' Some cars came with them as original equipment. Stewart-Warner still makes it, I think (see the left item in this photo (http://www.jalopyjournal.com/forum/attachment.php?attachmentid=213300&d=1155497932)).

What's glaringly remarkable is that it's OK to monitor vacuum, but the scale is WRONG. It's marked (in red) to indicate that low vacuum is bad. That's wrong. Low vacuum is good, provided I use it alternately with coasting (and provided that I also strive for high gear). Low vacuum is only bad when I'm persisting too long in a low gear, and when it means I'm creating excess kinetic energy that will ultimately be consumed by the brakes, instead of by coasting.

People are still very confused about this. I notice with great amusement a bunch of Camaro owners discussing this recently (http://www.thirdgen.org/techboard/tech-general-engine/464022-economical-driving-vacuum-gauge.html), saying things like this: "It's pretty well accepted that the greater vacuum reading you can get while cruising around the better your economy will be." Wrong. (BTW, I used to drive a '68 GTO, so I have no ill will toward Camaros, or other Detroit muscle.)

P&G driving can be FUN because it involves accelerating. Accelerating is fun, and it's a good thing, as long as the excess kinetic energy will ultimately be used in coasting, rather than consumed in braking.

[dosco]

If you found the link on another site, I think I'd like to see it, if you have it handy.

Here it is: http://www.tc.gc.ca/programs/environment/climatechange/subgroups1/vehicle_technology/study2/Final_report/Final_Report.htm

It's rather long, but I found it very very interesting that they remapped the contour charts that were in the speed article, accounting for 4-valve heads, turbos, etc.

Good stuff there.


Good point. I see what you mean. P&G is a challenge because it violates our old habits and expectations. It also has to be done skillfully, and with planning.

Exactly.

[PaleMelanesian]

Thank YOU for the compliment. Yes, it's all a constant refinement game. The cold winter showed me some flaws in my technique, and I refined them. Now, with warmer weather, I'm doing even better. Details like starting the pulse just before an uphill, and pulsing partway up, and the coasting up and over the crest. The uphill gives you more load, and makes it easier to hit that peak BSFC point. Then the downhill is free.

And it IS fun! :)

The vaccuum gauge is correct if you're applying it to steady-state cruising. Which is not one of the "70% or off" options. But in it's place, it is useful.

The grill block is more for faster warmup than it is for aerodynamics. My normal driving doesn't go over 55mph speed limit, so I'm not even going that fast.

[monroe74]

dosco: "Here it is"

Thanks very much for the link. Yes, I had seen that. I think that was linked in another thread around these parts. I agree, it's very interesting, and it supports the ideas expressed in the other article you cited.

pale: "it's all a constant refinement game"

Yes. And I think it also lends itself to a steady commute, where you're driving to the same place every day (over an identical route, or a route with minor variations; also probably at the same time of day, mostly).

For most drivers, that sort of driving is probably a large percentage of total driving. But we all sometimes drive in unfamiliar circumstances (and for some of us that might be a very large percentage of our total driving). Then P&G (and related techniques, like EOC) can become more challenging.

"The grill block is more for faster warmup than it is for aerodynamics."

Makes sense. I wonder if maybe it also helps the engine maintain warmth while you're gliding. The engineers who designed your cooling system probably didn't anticipate that the engine would spend a lot of time idling (or off) in a 45 mph wind.

"The vaccuum gauge is correct if you're applying it to steady-state cruising."

True. But that really just boils down to this guideline: if you must travel at a constant speed (for whatever reason), then the best you can do is just use the highest possible gear. And if you can, choose a lower speed. I think someone being guided by a vacuum gauge is really just applying those rules. But they're being misled, because they're being encouraged to adopt a constant speed, when P&G is better.

[PaleMelanesian]

I occasionally take a different route for that very reason - to keep myself fresh on unfamiliar roads.