Yea I've played with pulse and glide, most of my area doesn't really allow for it, the ground is more or less flat, so no opportunity to off coast down hills. I played around with it in my corolla auto at the time. About best in cruse mpg was something like 55mpg at around 45mph (basically the lowest speed the trans would let me go while lockup + 4th gear). Pulse and glide after a few attempts I got stopped to stopped mpg of around 65-70mpg. That's pulsing to like 45-50mph and gliding to 0mph. I think trying to average something like 40mph it was more like 55-60mpg. Still a large improvement, but the effort involve, traffic, etc I determined it wasn't really for me. With a manual trans and efficient take off and shifting, I suspect the numbers could be much better.
I've kind of ran with drive the vehicle as efficient as I can with more or less minor mods. Pulling up to 44mpg out of my corolla wasn't half bad when it's rated 32mpg highway, but that's with like 3 stops in a ~45 mile trip at around a steady 45mph speed. Pretty ideal for mpg. I have half a front belly pan on it, lower grill block, hood sealed, passenger mirror delete. Driving habits were by far the largest effect, the mirror delete and grill block I'd say are next biggest changers.
I actually was thinking about the mirror deletes, not sure what the legal status would be, but it seems like having a couple small screens and having backup camers on say the front corner of the car facing back would give a pretty nice view of the blind spot and an aright camera angle for backing up (atleast as far as side mirrors go).
That's pretty neat the prius engine should fit in my car, not sure how crazy the ECU would be about an engine swap, and like you say, the mpg difference probably isn't worth the effort, but the echo isn't that common, however the prius seems to be everywhere. Back a while ago I was researching the prius and at that time the results suggested the engine basically only worked in the prius so it's value wasn't great. I think I remember seeing a prius engine for $100 on craigslist around that time lol.
Another thing kind of dawned on me recently too. I kind of already knew it kind of, but it was just what I thought. Basically longer stroke vs bore size is more efficient and gives better mpg. That's effectively a truck engine and lacks big hp numbers but generally has good torque figures. I can't say how great this source is, but it seems to make a lot of sense even though it's in a 2 stroke context.
https://achatespower.com/stroke-to-bore/
Based on that logic, the echo 1.5L 1nz engine sounds to be a pretty good engine for mpg. The bore x stroke is 75×84.7mm (0.885 ratio), the corolla 1.8L (stroked 1.6L) 7a is 81x85.5mm (0.947) and the 1.6L is 81x77mm (1.05). From the limited experience I've had with the 4afe engine, it gets worse mpg and has lower power output. It seems pointless when the 7afe is better all around.
A while back I watched a video where a guy took equipment engines and swapped them into small trucks and such and were claiming some pretty crazy mpg figures, I'm thinking an f150 he claimed like 30-35mpg with the 4 cyl diesel engine. They where small engines, probably 40-60hp. Clearly diesel vs gas is hard to compare for the bore x stroke thing but the same logic should apply.
Makes me wonder what the ideal bore to stroke ratio would be for the best mpg and size the engine's displacement for the power requirements. Yea bigger engines weigh more, but in theory if the engine is the ultimate mpg design and you need 50hp from a 3.0L to have alright drive-ability vs a 1.5L 100hp and it's more fuel efficient, then that could be an interesting research point.
Clearly there's a point of no return, there's a point when the stroke will be too long and give negative effects or physical issues (piston speed, friction points, vibrations, etc), but I figured it's an interesting thought experiment. Too bad there wasn't a solid consistent reproducible test that could be done across engine designs to score their fuel efficiency in some standard way independent of the vehicle it's in.
Also it's kind of ironic that my diesel truck has almost a square bore/stroke design (same number, or 1:1 ratio) but has a low hp rate for it's massive size. 104.4 mm × 106.2 mm (0.98). 215hp and 450 ft-lbs of torque. I really thought it would be a lot longer stroke being diesel since diesel fuel burns so much slower and such.
To compare, here's a Perkins 3 cyl diesel for a tractor: 91 x 127mm (0.717) and 17.4:1 compression ratio. It's 2.5L, 45.5hp and 121.7 ft-lbs of torque. Scaling it up to 7.3L gives 132.9hp and 355 ft-lbs of torque. Generally hp/torque scales up linearly with displacement with the same designed engine, atleast based on my understanding and what I've read.
One more Perkins diesel engine, one that's higher compression ratio (23.3:1). 84x100mm (0.84), 41.6hp, 105.2 ft-lbs, and 2.2L. Scaled up that's 138hp and 3.49 ft-lbs. Pretty interesting, similar numbers even with higher compression.
I checked the toyota's d4d 4 cyl diesel and scaled it up and it's almost double the numbers of my diesel, of course it's also about 10 years newer tech in it too. Kind of funny, around a 4L version of the engine would have similar power to my 7.3L engine and I bet the mpg would be a bit better too.
I know hp/torque isn't really a measurement for mpg effects, but I found the numbers interesting. Seems like for my truck, the best FE mod would be a modern engine swap, and the echo would probably be a 3-4 cyl diesel engine swap lol.
Getting kind of off topic, but I might have to poke around a bit more to compare similar vehicle mpgs with long vs short stroke with similar sized engines and such, ideally from the same company so the engine/ecu is setup somewhat similar. Maybe there's something to using old tractor engines to get really good mpg but with low hp.