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Old 04-23-2022, 02:43 PM   #10 (permalink)
Master EcoModder
Join Date: Jan 2012
Location: MI, USA
Posts: 571

92 Camry - '92 Toyota Camry LE
Team Toyota
90 day: 26.81 mpg (US)

97 Corolla - '97 Toyota Corolla DX
Team Toyota
90 day: 30.1 mpg (US)

Red F250 - '95 Ford F250 XLT
90 day: 20.34 mpg (US)

Matrix - '04 Toyota Matrix XR
90 day: 31.86 mpg (US)

White Prius - '06 Toyota Prius Base
90 day: 48.54 mpg (US)
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The data from Drifter's posts works well. While cruising, say 55mph in my case, push the shift control left and hold it, about 0.5-1 sec it will be in neutral. I do the action at the same time and the car coasts and the engine turns off. I only have one 30 mile round trip under my belt with that trick, but so far that seems to work. I think it's best to put it back in drive under the 42mph upper limit so the engine isn't needed to be on. Basically there's 2 electric motors, and pure electric motor mode (regen or electric power) max speeds are around 42mph. Above that it needs the engine spinning to keep the electric motor rpm's within spec.

I didn't know where the heat exchanger was located for the inverter. I should be able to at least do a 50% block off easily with no problems, unless the Prius's cooling system isn't massively over sized like basically every other Toyota I've owned. I think I left my scangauge in my dad's Lexus when we was working on it last. Is there a gauge to show inverter temp by chance? I really don't like the fact the prius doesn't give any real gauges. I'm used to 90's era vehicles I guess where you could see voltage, coolant temp, sometimes oil pressure, rpm, etc.

Another factor for kicking the engine on is the hvac system, if you demand heat from it, defroster, ac, etc it's another reason for the engine to kick on. Like when I very first got the car, the 12v battery was dead, so I put the heater controls to max heat, rolled the windows down and in around a 10 mile trip I'm pretty sure the engine didn't turn off while on the car dolly. The battery seems to be doing well so far, last time I checked it was at 12.55v which isn't quite full charged, but it's 90%+. To check the 12v state of charge, it needs to sit long enough so the flash charge goes away, letting it sit overnight is the easiest way I've been going. You could put a load on it w\o turning on the charge system if you recently drove the car, but it's not as accurate. In a "normal" car you can crank the engine a little but not start it to eat up the flash charge.

As far as electrical mods, I'd have to look at the wire diagrams, but I don't think there's much direct control for the gas engine besides what the gas pedal and shifter does. I watched a vid about an open source controller for the inverter which drives the electric motors. According to that vid they can make 80hp or so but that's with the engine deleted, and the sun gear welded, not quite the route I'm looking to go. A pure electric car would be neat if the batteries didn't cost $10k+. I suspect most of the engine control and all of the automated functions in the care is communicated over the canbus, so maybe it's possible to intercept messages, or control things manually over that network. I have basically zero experience with canbus though, I just know it's a network designed for in the car, and of course the raw data is 1's and 0's. The new scope I bought recently is fast enough to read canbus though, so could be interesting to peek at some time.

Small update for the thread, I've done a fair bit of reading, sounds like 55mph trips people average roughly 45mpg so I'm slightly above what I've been seeing at around 47mpg. I'm sure fixing up the front end will help things a bit.

ABA testing is a bit harder with this car since the hybrid battery is a factor. When I get some spare time I might have to drive north a bit where there's basically no traffic and do some testing on driving patterns and such for take off. It seems like as long as I don't actually floor the car, or take off too light, it gets roughly the same mpg. I'd like to try higher speed pulse and glide and see how that effects things too. I'm pretty sure I could automate the setup with an Arduino. If the slight pulse & glide works well, then I'd want some way to automate it for long trips on the expressway and such since most of the time the traffic can get around no problem, unless it's a person not paying attention (lot of them around my area too lol).

An idea just dawned on me. I've been pulling up my driveway normally, but then I have to back out. Since my road is a dirt road, the last 1/4 mile is slow enough it's always electric only mode. I could back in and probably use slightly more battery than coasting in. I suspect puting a load on the cold engine sooner might be a benefit instead of idling and doing nothing. The trip to the first corner (1/4 mile) is again slow enough where the car wants to run off battery only even with the engine running to make the emissions systems happy and such. Too bad I couldn't control that a bit more, but that seems to be the nature of newer cars.

Another idea I had last night was the gear ratio. Since my driving is at higher speeds, I suspect having the gearing slightly higher should help mpg. At least my own experience has been larger tires give better mpg on normal cars roughly equal to the size increase if driven right. I don't need the car to be a rocket or anything. The fun thing is how well would the computer respond to the change though. Say a 10% increase in tire size gives 5% better mpg. If 45mpg is typical for 55mph speeds, then that would put me right in the 50mpg range for my goal. Sadly, it looks like the prius has a smaller 5 lug bolt pattern than the other vehicles I have in my yard, so I don't think I have a bolt on larger tire to just test the idea with. Has anyone else tried larger/smaller tires on a prius vs stock? Clearly the in car reported mpg and speedo will be off, have to offset the numbers based on the % difference in tire size (effective gear ratio change). City mpg will be worse most likely because of the higher gearing is harder to accelerate and the heavier tire.

Another idea that might be hard to aba test would be running a tire with a higher load rating. The whole tire would be heavier, but the max psi would be higher too. Like my truck's load range E tires are 80psi max and I run them at that pressure. I suspect "small" high load range tires are hard to find. Closest thing I can think of would be for a trailer which aren't designed for on car use, handling and such might suffer.

I found one mention going larger size got better mpg, but it's a person delivering mail... they went up one side on width and claim they got the best mpg that way. The ~4% larger size they lost 4mpg. Their use case is the opposite to mine though, so 4mpg drop in city driving might mean a 4mpg increase for highway driving. If you count 55mph+ as highway, that's 90% of my driving. I suspect once winter time hits, I'll be looking for some winter tires, so I'll look at going larger for the added ground clearance and ABA testing with 2 tires of each size and rotating the tires front to rear should be a reasonable test, same rolling resistance and such.

Just found this chart, looks really interesting. Looks like 14-27mph steady speed driving gives 100+ mpg on the prius. 55mph says 65mpg which doesn't match my car, but it's also 263k miles and needing some work, weaker battery, etc. The post/graph was posted in 2007 so likely using nearly new cars for the tests. On a warmer day I did a steady state 55mph test and the mpg readout said 53mpg if I remember right. I reset the trip while going 55mph, and looked at the average before I slowed down for the corner, engine fully warmed up clearly. That puts me down about 18.5% from what the chart suggests I should be getting on an effectively new car.


Last edited by ps2fixer; 04-24-2022 at 02:42 AM..
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