Why does the ICE get such horrible gas mileage?

You need to put it into a car the size of a Geo Metro to get that sort of mileage. The Prius is a mid sized car.

Tom

 

If memory serves the combined passenger and cargo max weight for the metro was about 400 pounds. Its performance in crash tests was mediocre at best... I think one model year they managed a 4-5. I don't think the ICE in the Prius is inferior to the unreal crappy 3 cylinder that the Metro had. And I guarantee you if you put that 3 cylinder in the Prius Prius mileage would drop. The Camry & Prius are just much larger and more versatile cars than the Metro, you really can't compare them.

 

The fact that it's an Atkinson Cycle engine also has a lot to do with it. The engine wasn't designed to run alone.

 

<div class='quotetop'>QUOTE(OlsonBW @ Jun 13 2007, 11:01 AM) [snapback]460854[/snapback]</div>

In general, for a given vehicle size, hybrids will be substantially more efficient than straight gas cars. This is what Argonne National labs has concluded, and I believe they are a pretty good source of information on issues like this. So the generic answer to this is that fill-in-the-blank vehicle was a tiny car.

In particular, the Geo Metro weighed roughly half what a Prius weighs, yet the new EPA ratings show it got the same overall mileage as the Prius:

New EPA mileage ratings (www.fueleconomy.gov):

Geo Metro XfI, 1993, 43/51, overall 46
Toyota Prius, 2007, 48/45, overall 46

I believe the xfi was the most fuel-efficient version. The other versions of the Geo Metro got slightly worse mileage. It had a 50 hp engine, consistent with the light weight of the vehicle.

Geo metro Specs, 1993:

Specification 2-door convertible 2-door hatchback 4-door sedan
Wheelbase, in. 89.2 89.2 93.1
Curb Weight, lbs. 1753 1650 ]1694
Overall Length, in. 147.4 147.4 151.4
Overall Width, in. 62.7 62.0 62.7
Overall Height, in. 52.0 52.4 53.5

Toyota Prius, 2007, specs:
Wheelbase (in.) 106.30
Curb Weight - Automatic (lb.) 2932
Length (in.) 175.00
Width (in.) 67.90
Height (in.) 58.70

In particular, I'd say four adults in a Geo Metro would have been a tight squeeze. And, per EPA, no better mileage than a Prius. But you couldn't run a Prius with a 50 hp ICE.

 

The Geo Metro was a great car in that respect, like the Honda CRX HF in the other recent thread.

But it was a 70HP engine (at best) in a small 2580-pound vehicle (gross weight), giving a 0-60 time of about 16 seconds.
The Prius is a mid-size car that weighs 3800 pounds (gross weight, curb weight 2890), with a 0-60 time of about 10 seconds.

You are correct, higher gas mileages can be done, but not in a mid-size family car with all the usual amenities.

 

The ICE in the Prius gets phenomenal gas mileage! EPA 60 city 51 hwy; Consumer Reports 45 combined. You call that horrible? You CANNOT separate the ICE from the electrical components of HSD. They are a unit, designed to operate as a unit. Please remember that 100% of the energy in the Prius is generated from gasoline by the ICE. So ALL the mileage in the Prius is due to the ICE. If you were to put the Prius's ICE in a conventional car with a conventional drive train, it would perform poorly because it has relatively little torque.

Where do you get the idea that the Prius ICE gets "horrible" gas mileage? Do you mean because a few years ago, cars of half the weight got mileage almost as good as the Prius does today? Odd criteria, that.

Or are you assuming that the electrical side of HSD is somehow producing 20 mpg on its own, and arriving at the (mistaken) conclusion that the ICE "really" only gets 30 mpg???

They could, of course, increase mileage by reducing overall power. But the market would be unlikely to support such a car on a large enough scale to justify a big car company's investment.

Or if the technology overall were more advanced, they could get higher mileage. And, what do you know! they're doing that in the 2009 Prius! It just gets better and better from Toyota.

 

An engine doesn't have an MPG number. A vehicle plus a driving profile has an MPG number.

 

If you drive on a really low battery and most power comes from the ICE alone, you'll notice the difference in horsepower and torque. The Prius has trouble getting out of its own way and that poor ICE is working as hard as it can to accelerate the car.

 

the same argument can be made on why my friends who have Harley Davidson's and Honda Bikes will tell me that their bikes can get between 50 and 80 MPG. Stick that same engine inside a larger vehicle with 4 wheels and it is no longer as efficient because of the load increase not to mention that it is engineered for the best performance for that designated vehicle that it was designed for.

 

Hi Soylent,

I think you have that wrong. When the battery is low, the engine is pushing the car along, AND charging the battery. So, your probably only getting 60 HP to the car, and 10 or so to the battery. Kinda like driving a Geo-Metro, I imagine.

 

<div class='quotetop'>QUOTE(donee @ Jun 15 2007, 01:15 PM) [snapback]462391[/snapback]</div>

Which is why you take a MPG hit if you run the battery down, but you still get the battery assist when the battery is low (2 bars). Just say you theoretically stuck a 1.4L Metro engine in a prius the numbers most likely would drop down to 20 - 25 MPG, because of it being underpowered.
If you were to say stick a 2.5 L 6 cylinder in it it probably would get 30 MPG.

Or see what kind of mileage you get in a metro after putting about 1500 pounds of bricks or tube sand in it, to make it equal weight. (point of reference I think a refridgerator, weighs about 500)

 

i think its decieving looking at the MPG when accelerating from a stop, the number is so low it looks like the ICE Sucks at Efficiency (screen showing only arrows coming from ICE).... i think this is where the confusion is stemming from... caught me off gaurd for a sec too. but the ice indeed does not suck... well covered in everyone else's previous posts.

 

<div class='quotetop'>QUOTE(Soylent @ Jun 15 2007, 10:00 AM) [snapback]462379[/snapback]</div>

How often does the battery get that low? Maybe on a really long mountain pass? Or if you're stuck in traffic (just hope the traffic isn't going up a huge hill. I haven't heard many complaints, so it's probably a non issue most of the time. I think my 84' Westfalia had around 80hp, and it was a dog on hills. I heard someone say they had no problem on the Coquihalla, and that they had no problems, and it's a long climb there.

 

<div class='quotetop'>QUOTE(OlsonBW @ Jun 15 2007, 07:50 PM) [snapback]462681[/snapback]</div>

Larger engines are in actuality more efficient, they only get their bad efficiency wrap from being in vehicles that weigh 8000 pounds. Plus their transmissions are usually geared for a power curve.

As far as your Camry is concerned, there is no way you can consistently get 40 MPG in a Camry, I owned my Talon (Eclipse 180,000 miles) for 10 years, it had a 2.0L 4 cylinder and it was a manual shift, I almost always got a steady 32 - 34 MPG. Take in mind that this is an extremely aerodynamic light 2 door car. Now granted I never did any of the fuel saving Nascar tricks like riding the clutch, but I only pulled off 40 MPG tanks a handful of times, and all but one of them were taking 550 mile drives non stop.

Seriously though if your wife was pulling out 40 MPG tanks in a Camry she should easily be doing 65 - 70 MPG tanks in the Prius.

 

The engine as installed in the prius is good for at *least* 50 MPG
by itself, without any help from the hybrid system. Just look at
the steady-state highway numbers people are writing in. Even around
town, deliberately not utilizing the "hybridness" of the car, it's
good for that. You need to look at long-term averages, not the
little drop you get to 9 MPG just when starting off from a light.
.
_H*

 

http://www.caranddriver.com/columns/11310/...g-minicars.html
http://www.detnews.com/apps/pbcs.dll/artic...309/1148/AUTO01
http://www.epa.gov/otaq/cert/mpg/fetrends/420s06003.htm

Chogan is right about the size and weight growth of vehicles.

 

Hi All,

I am not so sure that its large engines that are so efficient, as much as the right-sized cylinder. To get power, you want a light piston, to reduce reciprocating loads and run at high rpm, with little torque penalty for the smaller piston - ala 2.4 liter Formula 1 engines.

But, if one is trying to maximize efficiency, the thing is to minimize pumping losses. And circles have much more area with small change in diameter. A piston and valves can have larger area with a larger piston. I am sure there is more too this, like the displacement volume/pumping passages area ratio. But if you go too large, the reciprocating forces result in higher normal friction forces at the RPM required for the marketplace power level.

Along with this is the vibration issues of engine design. Four cylinder engines are often criticized for vibration, but the fact is they have perfect primary balance - two pistons up as two pistons go down. The vibration is due to secondary balance - con-rod momentum being synchoronized for maximum vibration. As con-rods are only tilting back and forth to make that vibration, its relatively easy to make a vibration damper - ala the Isuzu (also used by Porshe) rotating mass device.

So, when it comes to putting this altogether, one might think a 3 cylinder 1.5 liter might have been a good Prius nex-gen choice. But, the issue is that engines are usually for more than the single car-line they are in, especially at Toyota, where reliability is a great concern. There are economics at work. If you make a custom engine for one car line, will there ever be the money to get the engine solidly figured out? And also is there a good vibration design for a 3 cylinder engine? By making it a 4 cylinder, its usable in the Corolla, and there is lots of money to get it right. By making it a 1.8 liter, one gets the larger more efficient cylinder.

And the 1.8 liter engine certainly helps out the specsmanship people. Who look at a car with 110 HP, and pooh-pooh it, even though its got the equivalent performance to a 145 hp car. So, it looks like a win-win. But still there looks to be Fuel Economy oportunity for the Gen 4 Prius, when the production becomes large enough for a custom engine - 3 cylinder 1.5 liter, with turbo and offset crankshaft.