Being disappointed by my fairly low score in this weekend's fuel economy run, and wondering if I should have P&G'd instead of lean burning, I did one lap on a short course of country roads to see what P&G would get me.
Lean burn: 69.7mpg on a 6.4mi loop @ steady 50mph
P&G: 71.6mpg on the same loop @ 45-55mph
During the first run, I just "drove normally". That means cruising in 5th gear at 45mph in one section and 50mph in another, and slowing down if that's what it takes to hold lean burn. During the second run, I did P&G. When vehicle speed dropped to 5mph below cruising speed, I'd tap the throttle to re-start the engine, give it 60% throttle in 3rd gear (2200-2700RPM), then shift to N and hit the engine kill switch when I got to 5mph above cruising speed.
It was a 6.4mi loop of country roads, with five complete stops and four right turns. The course was somewhat flat, there was little wind, and no traffic on my tail. Conditions: 53°F ambient, engine fully warmed up, electric assist switched off.
P&G didn't beat lean burn today. I think there are conditions under which it would, though.
The course I laid out happened to be about as good as it gets for lean burn. If I had been cruising at 120mpg instead of 80-90, then lean burn would have wasted more revs compared to P&G. Maybe my 3rd gear P&G was sub-optimal? Would I have gotten better results in 4th?
I will P&G at the next hilly fuel economy run for sure, but until then, I'm going to keep on cruising in lean burn, knowing that my efficiency is near P&G levels, without the fluctuation in speed.
In effect uphills and downhills give me a sort of terrain-based P&G: I shut off the engine and glide on downhills steep enough to maintain speed coasting. Except on steeper downhills where I would pick up speed, and there I leave the engine on, foot off the gas for fuel cutoff, and add in regeneration to top up the battery. I drive the uphills without assist, letting speed bleed off a bit near the top if I know the downhill afterwards is steep enough to regain the speed I lost.
On dead flats and slight downhills, I try to mosey along in LB rather than P&G. In a non-hybrid without lean burn I'm more inclined to use P&G.
Sometimes in the Insight-I I'll let the speed droop a bit when there is no traffic around, accelerating back up to my target speed as a cluster of cars comes up from behind. Sort of a traffic-based P&G.
__________________
2006 MT
MIMA w/FAS module
various mods to driver
I find that I can't lean burn for about 30s after a long engine-off. So, I don't think you could acclerate in lean burn while doing pulse and glide.
But yes, I do like to use 3rd gear lean burn for climbing hills when I can't climb them in 5th gear lean burn.
I have an idea that I think would save a tiny amount of fuel when you're going faster than you can lean burn but there's no traffic behind you: "pulse and lean burn". Accelerate to 5mph faster than your cruising speed at 65% throttle, then enter lean burn, which causes you to slowly lose mph. Do that until you're going cruising speed minus 5mph, then repeat.
...When vehicle speed dropped to 5mph below cruising speed, I'd tap the throttle to re-start the engine, give it 60% throttle in 3rd gear (2200-2700RPM), then shift to N and hit the engine kill switch when I got to 5mph above cruising speed....
Hi Robert,
You'll get more mpg by shifting slightly below 2000 rpm.
That's because the air intake resonator has null at around 2000 rpm, and power drops off at this point. The resonance is greater at about 1600 and 2200 rpm.
For best mpg's, I typically shift around 1900 rpm when I can, with little traffic around. It makes getting up to speed harder, but really improves the gas mileage.
Replacing my current hot air intake with one that's hotter and includes the stock resonator is on my to-do list.
Do you think I could have P&G'd at these speeds in 5th gear? That would place me at 1400-1700RPM. I started to do it in 5th, but it didn't seem to "like" 1400RPM and heavy throttle application. Though it's true that I'm very unfamiliar with that operating regime.
Pulse and glide seems extremely difficult with this car. I've read up on people who are doing it at CleanMPG and I have my own experiences in my other car, which I've managed to get a little over 25% over the highway EPA rating with through forced engine stop and pulse and glide.
Those on CleanMPG doing it say that your pulse should be 25% and glide around 75% or better. The "problem" that we have is the engine is small, we don't get the power to pulse 25% of the time and glide. So I don't see how the 1900rpm or 1700rpm numbers make sense. I can't pulse at those speeds, I sometimes can't even maintain highway speed on the slightest uphill at 1700rpm. So, this means it requires dropping a gear or two to do it.
We need to revisit the idea of why P&G works. Engines are more efficient if they are produce a greater amount of power, to a point, at the engine speed they are at. If you sit with a car running at 3,000 RPM in neutral, you waste a whole bunch of gas accomplishing no work. So with pulse and glide you make those engine revolutions work for you by putting your engine under load by speeding up and then shutting it down while you coast.
...I see the Insight being a bit different, at least on the highway in lean-burn. The car is geared very low for its engine size, it right about where my 3.4L V6 used to drive at in top gear but it has less than 1/3 the air and therefore less space to fill with fuel and produce power. Granted the Insight is probably half the weight, it really isn't my point. My point is that the small displacement is putting the engine into a more efficient high load situation by spinning less revolutions, pumping less air, and therefore putting less fuel into that air. Lean burn helps because we can reduce pumping losses and the burn is a little more efficient (also hotter) when lean.
So basically alot of the advantage of pulse and glide goes away with a small displacement lean burn engine using low RPM gearing. Can it improve with pulse and glide? If you have a stock Insight without any mods disabling assist like I do, if you are on the highway I doubt it. Outside of lean burn I can't get it to speed up fast enough in a higher gear and lower gears the assist wants to kick on without enough engine load to make the pulse effective.
I pulse and glide on slower roads with no traffic, there is a road that I turn on when I'm coming back home after work that nobody is ever on. I speed up to 50MPH and shut the engine down when I hit the stop sign I'm at 10-15mph without much to lose when I stop.
I'm not saying that the advantages of pulse and glide aren't possible with this car at highway speeds of, say 55mph or higher, but I think it will be harder to do considering the efficiency of the setup causing diminishing returns. It's easy with my Prizm to get an extra 25% in he summer using it but that is due to its high RPM gearing and excess power leaving me outside of load.
If anyone has decent gains from P&G at 55mph, I'm all ears.
Pulse and glide seems extremely difficult with this car. I've read up on people who are doing it at CleanMPG and I have my own experiences in my other car, which I've managed to get a little over 25% over the highway EPA rating with through forced engine stop and pulse and glide.
Those on CleanMPG doing it say that your pulse should be 25% and glide around 75% or better. The "problem" that we have is the engine is small, we don't get the power to pulse 25% of the time and glide. So I don't see how the 1900rpm or 1700rpm numbers make sense. I can't pulse at those speeds, I sometimes can't even maintain highway speed on the slightest uphill at 1700rpm. So, this means it requires dropping a gear or two to do it.
We need to revisit the idea of why P&G works. Engines are more efficient if they are produce a greater amount of power, to a point, at the engine speed they are at. If you sit with a car running at 3,000 RPM in neutral, you waste a whole bunch of gas accomplishing no work. So with pulse and glide you make those engine revolutions work for you by putting your engine under load by speeding up and then shutting it down while you coast.
...I see the Insight being a bit different, at least on the highway in lean-burn. The car is geared very low for its engine size, it right about where my 3.4L V6 used to drive at in top gear but it has less than 1/3 the air and therefore less space to fill with fuel and produce power. Granted the Insight is probably half the weight, it really isn't my point. My point is that the small displacement is putting the engine into a more efficient high load situation by spinning less revolutions, pumping less air, and therefore putting less fuel into that air. Lean burn helps because we can reduce pumping losses and the burn is a little more efficient (also hotter) when lean.
So basically alot of the advantage of pulse and glide goes away with a small displacement lean burn engine using low RPM gearing. Can it improve with pulse and glide? If you have a stock Insight without any mods disabling assist like I do, if you are on the highway I doubt it. Outside of lean burn I can't get it to speed up fast enough in a higher gear and lower gears the assist wants to kick on without enough engine load to make the pulse effective.
I pulse and glide on slower roads with no traffic, there is a road that I turn on when I'm coming back home after work that nobody is ever on. I speed up to 50MPH and shut the engine down when I hit the stop sign I'm at 10-15mph without much to lose when I stop.
I'm not saying that the advantages of pulse and glide aren't possible with this car at highway speeds of, say 55mph or higher, but I think it will be harder to do considering the efficiency of the setup causing diminishing returns. It's easy with my Prizm to get an extra 25% in he summer using it but that is due to its high RPM gearing and excess power leaving me outside of load.
If anyone has decent gains from P&G at 55mph, I'm all ears.
This is exactly my experience. As I said above, I find P&G useful in the Insight-I only on rolling terrain where I "Pulse" the uphills and "Glide" the downhills. I don't use it on strictly level ground or on downhills too gentle to glide on.
__________________
2006 MT
MIMA w/FAS module
various mods to driver
....So I don't see how the 1900rpm or 1700rpm numbers make sense. I can't pulse at those speeds, I sometimes can't even maintain highway speed on the slightest uphill at 1700rpm. So, this means it requires dropping a gear or two to do it.
I'm not sure if your talking about my quote above, but I have found that the engine is very sensitive to activity of the resonant chamber mounted on the intake tract.
Several years ago, I did some uphill testing that was reported here to the effect of the intake resonator and how I had heard that several had removed it to install a hot air mod.
This will work only if you always keep your revs above 2000 rpm, since the resonator does give an measurable boost from 1300 to 1600 rpm's or so, and then again above 2200 or so.
There is a distinctive null about 1900 or so, and that's why I tend to shift to the next higher gear about 2000 rpm or so.
I haven't tried too much P&G, but did read that the winner of the 2008 Madison Hybrid Fest varied his speed from 30 to 11 mph and got about 170 mpg in the contest, so it can be done with an Insight, although at a speed most people would not care to drive.
I have an 02 CVT, and after reading the threads and the library, I brought my commute average from 51mpg to 62mpg with only 1 major change. I keep my rpms at about 2200 (one bar above 2000). It does cause me to run below the speed limit (about 56 - 58 mph on the flats). But the smile on my face to be getting such good mileage can't be beat. Using a little push on the hills (keeping it safely above 54) it works great!
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Experiment: Insight Lean Burn versus P&G
