I was bored one day and started fiddling with some numbers on a spreadsheet, thinking about whether the Prius estimate of "about 50-70% speed = mpg" (40mph ~25mpg) acceleration target was applicable to anything else. I sometimes have to drive the family van around, which is fairly old and is EPA estimated for like 22 mpg on the highway. All I have for instrumentation is a Tach and a somewhat laggy i-MPG display, so I'm never entirely sure if I'm in that 70% load zone, couldn't find a BSFC chart so I'm not sure what kind of "optimal" MPG to expect either. So with the sketchy assumption that cruising at 50mph with ~25mpg is reasonable to expect, I multiplied it by 0.6 to get 15mpg, then copied that ratio down the speed range (so like, 20 mph = 6 mpg), maintain near 2K RPM. Does this seem like a reasonable set of napkin assumptions to make? (2008 Sienna)
This topic is beyond me, but I have a couple of thoughts for you to ponder, and the search image results about gearing is food for thought as well. It behooves me to keep in mind that you're focusing on acceleration and keeping a specific range of load. I was almost off on a tangent in the at-speed and above ranges that do not apply. My brother would like your family car choice. He has a pair of 2009s, one for business hauling and one for wife and grandkids.
If you can't be sure of exact load, better to err on the side of faster acceleration, and get to cruise speed, with an automatic.
Yea that's pretty much what I'm doing, keeping the RPM near 2K when accelerating, spaced out with trying to coast where practical. Unfortunately it wants 45+ mph before it considers going into 5th, which isn't always practical, so I'm stuck rolling around in 4th. Somewhat doubtful how much coasting helps because of how draggy it feels, but 40 mph cruising is probably a distance away from peak BSFC due to how much horsepower this thing has.
Considering the aero, driving with load might be a better option than pulse and coast. The torque converter might lock up, even if fourth, then.
Sounds reasonable. I'm somewhat reluctant to use neutral too much, so that's probably what I'll keep in mind. Outside of slowing down for red lights, etc.
When I searched hypermiling techniques for the Sienna, I found people varied between neutral coasting and letting fuel cut-off do its thing when approaching lights, depending on distance to the light. You're already working the acceleration aspects, so you're well on your way. And of course the usual comments about tire pressure, steady speeds, removal of roof impediments if any (racks), removal of excess baggage.
I generally only use neutral coasting when not coming to a stop, but none of my cars air braked like a minivan.
For small cars, both our 6spd 2013 automatic & 2016 manual Elantras love to coast, holding speed. Extra distance from the stop light really helps to get the speed down, before the brakes are applied. With the 6spd automatic, I love coasting so the transmission doesn’t need to shift down through each gear. Of course, if hurry-hurry people are behind me, trying to push me toward a stop light, I’ll coast less. Maybe if it’s a wasteful pickup with over-bright headlights & KC lights (or any car with over-bright lights) in my rear view mirror behind me, I will coast all the way down. Accelerating the automatic in each gear a little quicker, I’ll ease off acceleration at the very low acceleration shift point, to get the next higher gear to upshift as early as possible. I’ll remain at very low acceleration, so the transmission doesn’t accidentally downshift. As the car accelerates a bit above the very low acceleration shift point, I’ll apply a bit more gas pedal. As I approach the next higher gear, very low acceleration shift point, I’ll ease of the accelerator & get the transmission to upshift early again. Continue the process until 5th gear is engaged. The 6th gear won’t engage till 43MPH (45 MPH with my over-sized tires), if I ease off the acceleration for the last time. If I’m on a flat back road, I can ease off to 41MPH & even down to 37 MPH (with my over-sized tires), 1200rpms & still hold 6th gear. Can really pile on the MPG, then.
In the 2019 Fit LX CVT , I find that it's easy to hold at 2000 RPM when accelerating up to speed. It's hard to check with the SG , but it seems to run at 25 MPG , or about the same as the Prius ( also hard to determine ). I rarely find times I can shift to neutral , but my experience in this car has been limited. After Tuesday , the Prius will be gone and I will have a lot more time in the Fit.
I had the Dodge Caliber CVT. I liked it very much(the CVT, not the Caliber body) & was in the top 5% MPG on the Caliber forum, & beat the people with the 5spd manual transmissions. I loved it in the mountains, being able to have the perfect gearing for ALL slopes & conditions. The Dodge forum & reliability data showed many mechanical problems, tho mine was very good. But, the Caliber still wasn’t efficient, & I was wondering when my CVT might have trouble. Anyhow, that is why we have the Elantras now. Love the Elantras (specially the manual efficiency), but still miss the CVT elegance.
I got some testing done with OBD readouts for the van, it seems at about 60-70% load the engine was using about 2.3 to 2.7 gal/hr. Weird thing I noticed was the throttle valve seeming to never open more than like, 20 degrees, though I don't really have a way to film the throttle valve and correlate that to what the readouts claim. I guess at lower RPMs, the airflow is slow enough that the ECU can't be bothered to open up the throttle all that much?
My old carbureted 1979 Plymouth Champ, had 3 valves per cylinder, two being regular & small intake valves. At low rpms, the small intake valve would activate, while the regular intake valve remained seated. The idea was the small intake valve would increase the velocity of low rpm, slow air on the intake stroke, better swirl-mixing the fuel-air on the compression stroke & obtaining more thorough combustion on the power stroke. Theory I know, but the Champ would often get 45-47MPG, 43 MPG in the mountains, & during ideal circumstances, did deliver 50MPG. MPG was much higher than my 1973 1.4L Subaru AND the 1984, 1.5L Toyota Tercel. In its time period, I always was happy with Champ’s MPG.
I remember reading about that for intake valves (V-tec, etc), didn't realize it could be applied to the throttle valve as well. I always expected "80% load" to be, well, throttle valve at 80% opening.
The ECU is smart enough to know that not much throttle opening is needed at low engine speed to provide a moderately high manifold absolute pressure (i.e., lowish vacuum).
