The Prius Experiment

[ps2fixer]

Where are those pizza pans from? they look quite well for that style of "hub cab". My rim rings are already damaged by the last owner, so I don't have any attachment to them. Might just drill and tap the actual rim though since it's not a huge deal and will secure them better.

I normally go with plastic since they are lighter and the balance of the cover is less critical when there's less weight involved.

[Blacktree]

I got them from WalMart, about $5 each. But I had to go through a lot of them, to get 4 that were in decent condition.

Side note: If the pizza pan wheel covers work as intended, I'll probably make something that attaches directly to the wheel. Because I also would like a more secure attachment.

I have some experience working with composites (i.e. fiberglass). So maybe I'll make some wheel covers and a grille block from fiberglass... or maybe carbon fiber? That would be cool. But that's a "maybe someday" thing.

At this point, I think I've exhausted all the "cheap and easy" aero mods to reduce drag. I would also like to try a belly pan and rear wheel skirts... maybe a drag spoiler as well. But those are more involved projects.

[ps2fixer]

I see, I'll have to try seeing what they have locally at my walmart. Hopefully they are stainless so they don't rust.

The fiberglass route would probably work well, but I think that's heavier than plastic. You could get a sheet of ABS plastic from Lowes or Home Depot I'm pretty sure, cut it with a saw (slow) and shape it, then you can use a heat gun to dome the shape of it some. Probably not easy to make it look as nice, but probably one of the lightest options. Old school hub caps were metal and pretty heavy, so as long as they are centered and balanced somewhat well it should be fine, just have to make sure they don't pop off too easily.


I've wondered if a small supercharger would help or hurt mpg. Prius it might not work too great on, but the concept is it would be sized to run the engine well at take off rpm's and do little to nothing ideally at cruising rpm so there's not much of a pumping loss from a more closed throttle. I've seen it mentioned quite a bit that supercharging or even turboing an engine can give the same, maybe slightly better mpg if you don't drive it harder than you used to. Clearly that's a more involved mod as well and probably not worth the costs if it does even save fuel at all.

[Piotrsko]

Superchargers would be belt drive? So some loss when adding boost from drive system.

[Blacktree]

Generally speaking, adding boost to a gas engine increases BSFC. You have to run it a little rich, to avoid knock. A diesel engine is a different story, because knock is not a concern. So you can run it super-lean.

[ps2fixer]

Originally Posted by Piotrsko

Superchargers would be belt drive? So some loss when adding boost from drive system.

The concept of supercharger would be belt drive, and that's because you'd want boost down low like 2500-3000 rpm. I'm sure turbo's can be sized so they boost pretty low, but I think they are more 4000-8000+ rpm type of range typically.

Originally Posted by Blacktree

Generally speaking, adding boost to a gas engine increases BSFC. You have to run it a little rich, to avoid knock. A diesel engine is a different story, because knock is not a concern. So you can run it super-lean.

There's a lot of factors involved with boosted engines. What's your source for the increase in fuel use? Just wondering if there's a theory behind it, personal experience or what.

Engines normally retard timing to prevent spark knock, that's how it's done on Toyota's at least. My 1990 Lexus LS400 is 10.5:1 compression ratio and calls for 90 octane min. I sometimes run 87 octane in it, and I can feel the timing being pulled (knock sensors pick up the knock and computer responds by adjusting the timing). The amount of fuel injected should be more or less the same. Not quite the same as boost, but this same car had a dealer installed option for a super charger, literately a bolt on kit, no tune change to the computer. I don't recall but I'd assume it requires higher octane fuel, but the same system the pulls ignition timing should work with the boost, at least to a point (it's max output is like 7psi).

On the GM side of things, when the engine gets hot, that has a similar effect as higher compression or extra boost, I've seen in their tune tables that they pull ignition timing, but I don't remember seeing anything in the fuel table for the same region. Again, not directly boost related, but somewhat related, preventing spark knock.

One benefit of having a boosted engine (super charger or turbo) is the fact you can use a much smaller engine to put out the power of a bigger engine. I don't think too many cars use that concept though, but I'd think it could potentially help FE having a little 1.8L making say 200hp with boost vs an 4.3L GM v6 which makes about the same hp. I would think there would be less losses with the inline 4 and smaller parts than the big v6. I guess a better example would be like a 500cc motorcycle engine powering a small car and having around 100hp (just guessing, but something like 15lbs of boost, it would be clearly a pretty hot setup). The Corolla 1.8L in my 1997 was around 110hp.

[redpoint5]

The new Integra is making 200hp from a 1.5L engine.

Very disappointing that it only gets 30 MPG. That's what my 20 year old 2.4L TSX gets, and the same horsepower.

I'm dubious of the value of a turbo for fuel efficiency reasons.

https://www.caranddriver.com/reviews...integra-drive/

[ps2fixer]

Power: 200 hp @ 6000 rpm
Torque: 192 lb-ft @ 1800 rpm

That's quite unique, maybe that's common for turbo engines, but peak torque being that low should be pretty great for ecomodder drivers. My corolla's engine's peak torque was at 2800 rpm, the 1.6L smaller engine version of the corolla peak torque was at 4800 rpm. It seems like the 1.6 gets a lot worse mpg, but it's also mated to a 3 speed trans, no over driver, no lock up torque converter.

Anyway, take any car that produces 200hp and compare the mpg, I suspect they will all be around 30mpg. A smart driver I'd think could get a lot better mpg out of the small engine than the larger engines though. Like for the era of car I drive, I'd have to have a v6 camry to get around 200hp, and those are rated for 27mpg highway 20mpg city. That's a 2001 car vs 2023.

I'm not sure how the hybrid system would respond to the prius engine creating more power, I assume it would balance out fine. Of course the prius engine is pretty special with it's valve timing, forcing air in would make it run at a higher effective compression ratio, and since the static compression is at 13:1, it could be really easy to go past the ability of the fuel to resist spark knock. I'm not even sure if the delayed intake valve effect would still exist with the engine having boost.

[Blacktree]

Originally Posted by ps2fixer

What's your source for the increase in fuel use?
...
Engines normally retard timing to prevent spark knock, that's how it's done on Toyota's at least.

Decades of experience has taught me these things. Typically, a boosted engine cuts spark timing under boost AND runs rich, to prevent knock. Because if you push your luck, you'll be replacing broken piston rings and/or fragged pistons.

[ps2fixer]

I see, I'm actually working on an engine simulator to test stock computers, would be interesting to simulate engine knock (knock sensor) and see if it only pulls ignition timing, or timing + adds fuel. I don't have any computers from an engine that had boost factory though. Would be interesting to see the data on it though.