How good mileage could the Prius get

<div class='quotetop'>QUOTE(Per @ Jun 8 2007, 04:02 PM) [snapback]458276[/snapback]</div>

Uhm...you think the highest mileage car onsale now is somehow not optimized for mileage? Fuel economy.gov gives the 1988 Honda CRX HF a combined rating of 41 mpg. It gives the Prius a combined of 46. And the Prius is classed as mid-sized, the CRX as a two-seater.

 

I think what Per means is the Prius is optimized for fuel economy, but it does have to conform to emissions standards, as well. If the Prius didn't have to follow any sort of restrictions, would it get better fuel economy. Like if the Prius didn't have a need to warn up a catlytic converter then it'd get better FE.

 

<div class='quotetop'>QUOTE(MegansPrius @ Jun 8 2007, 04:16 PM) [snapback]458285[/snapback]</div>

A lot of things that manufacturers do to meet emission regulations and counterproductive for fuel economy. Take EGR for example. For greatest efficiency and power you would want to maximize combustion temperature to maximize cylinder pressure. But increasing the combustion temperature also increase NOx so EGR was invented to cool down the temperature as well as give some of the gases a second chance to burn off pollutants. EGR is good for controlling NOx and helping reduce smog but reduces fuel economy.

To answer to OP's question, no CO2 is not a concern, at least not in the USA. The EPA and CARB do not list CO2 and a pollutant and have not limits on emissions of CO2.

The Europeans and the rest of the developed would with the US and Australia being the exception believe that CO2 is a huge concern and is the primary cause of global warming.

 

The Prius burns more gas than it would have to do during the first few minutes, in order to heat everything up quickly. Depending on ambient temperature, I'd say I get 25 mpg during the first 5 minutes in January in North Dakota. Higher in warmer temperatures.

What it "might" get without that warm-up depends on how much weight those first few minutes carry in your total driving time. If you drive a half an hour, eliminating the anti-pollution measures might raise your mpg by an insignificant 1 mpg. But if you live 5 minutes from work and shopping, you might get 5 or 10 mpg more overall.

Nowadays a lot of people are buying the Prius just because it's a good reliable car and burns less gas than any other gas-burning car, excluding the two-seater Insight. But back when I got mine, and the conservatives were all saying you can't trust "new" technology, most of us bought the Prius more because it's clean, than because it requires less gas.

I admit, however, that I was disappointed by how much gas it burns. That's why I bought Yevette. She doesn't burn any gas. All she burns is electrons, and she goes an incredible billionth of a billionth of an inch per electron. (Electrons are very, very small.)

 

<div class='quotetop'>QUOTE(Per @ Jun 9 2007, 10:35 AM) [snapback]458415[/snapback]</div>

Again, it is apple to orange.
Why don't you compare it between midsize sedans?

Ken@Japan

 

<div class='quotetop'>QUOTE(Per @ Jun 8 2007, 08:35 PM) [snapback]458415[/snapback]</div>

Well, there is thing called YMMV. When I drive highway I get the mid-50's, no problem. But your point is true, if the Prius could get better mileage if it didn't also try to be a mid-size four-door car with amenities and safety and pep that Americans expect today (for some reason we can't tolerate manual locks and windows and stick shifts anymore, not to mention being without airbags on all sides). If you try to sell a rebranded 1988 Honda CR-X as a new car today, I don't think it would sell, even if the EPA allowed it. It doesn't matter what mileage you get, if nobody drives it. The Insight is a good example - it got better mileage than the Prius, but with a significant hit in comfort and space.

The Prius is partly a product of its time, partly a product of the future. The CR-X is recognized as the pinnacle of 1980's technology for fuel economy. Small cheap cars then were very light and only needed 70+ HP for decent acceleration. Even my 1987 Nissan Sentra got about 36 mpg average and 40 on the highway (no power steering, no power brakes, no power windows or locks or seats, no automatic transmission, but it did have AM/FM/cassette and A/C, which my previous car did not). But I'm sure it spewed out several times the pollutants that the Prius does.

Supposedly there will be 3 variations of the Prius in the upcoming years - a Yaris sized version that should do what you're talking of, the current mid-size car, and a larger Camry size. I could see us buying the big one for road trips and my wife's longer commutes, and I'd buy an electric truck for my short commute and running to the hardware store. Of course, most of the time I ride my bike to work anyway, that gets the best mileage of all.

 

<div class='quotetop'>QUOTE(Per @ Jun 8 2007, 08:35 PM) [snapback]458415[/snapback]</div>

As is everyone's idea of highway driving. If I slow down to 55-60 mph, I can easily match the CRX's claimed 56 mpg. I owned an 88 Civic, mine was an LX sedan, not the CRX, but I remember well looking at one when I bought. That is a much smaller car than the Prius, as the others have mentioned. If you factor in the size, the Prius beats the CRX hands down. The Insight hybrid is roughly CRX sized and beats it in mpg. The Prius is much larger, seats five, carries ~14 cubic feet of cargo (almost same as Camry's trunk) and still gets slightly better mpg than the CRX HF.

Prius = big improvement over CRX HF. That was a neat car, and very good for the small slice of the market who could accept its tiny size. But no, it does not compare to the Prius in any way.

 

The way that the EPA calculates mileage has changed over the years. In the early 90's they started reducing their measured MPG by 20% in order to make the numbers closer to "real world" mpg numbers. Thus the 56mpg for the CRX needs to be reduced by 20% which would make it only 45mpg.

Even with the new change in the EPA rules (starting next year) the measured mpg numbers are reduced by 20%. The EPA.gov web site tells you this, but it is hidden in a bunch of other mumbo jumbo. Look it up.

This 20% reduction is why it is often possible to beat the EPA mpg numbers.

 

<div class='quotetop'>QUOTE(Per @ Jun 9 2007, 10:49 PM) [snapback]458618[/snapback]</div>

Many things to point out...
- weight : the base driving resistance is caused by the weight. CRX 900 kg vs Prius 1300 kg : 144%, CRX has advantage
- frontal area : CRX 1675 X 1270 mm vs Prius 1725 X 1490 : 121% (assuming they are quadrangle）
- Cd : CRX 0.29 vs Prius 0.26 : 90%
= frontal area X Cd = 121% X 90% = 108.9%, CRX has advantage

Bigger engine?
The CRX has 1.5 or 1.6 (SI) liter based on models.
Prius 1.5 liter engine is the Atkinson cycle which intake volume is less than 1.3 liter.

Ken@Japan

 

Per, your original question is still valid, just leave out the comparison. The Prius would get better mileage if it didn't have to meet strict emissions standards. It can't be sold without meeting those requirements, so it's really just an exercise in "what ifs".

So how much better would the mileage be? My guess would be 10-20% on short trips. Perhaps 5-10% on longer trips.

The implication that was almost stated is that we are generating -more- CO2 to emit -less- NOx, CO, and hydrocarbons. This is a demonstrable fact.

For example, a Mazda RX-8 (I use it because I have measurements for it - done during efforts to increase power) dumps about 15-20% more fuel into the cat. than it needs to just to produce power. This is to keep the cat -hot AND cool- (you can actually overheat a cat as well - the liquid fuel without oxygen can cool it). This is why it gets such poor mileage. In Mazda tests, it got 35-40 MPG -before- emissions work. It gets around 20 after.

 

Fair enough, but who actually drives at "constant speed on level ground"?

There are some nuts who can get 100+ MPG out of the Prius by doing that.

If, on the other hand, you actually drive on highways that have other cars, you end up slowing down and speeding up quite a bit. Putting the cruise on 75 works great in Wyoming, but it rarely works in California.

Highways aren't flat, either. Put the Prius on cruise and watch the energy monitor - you'll see just how much a little upwards slope can do to your mileage.

What the heck? You talk about "constant speed" in one sentence, then talk about regen in the next sentence. How does regen do ANYTHING AT ALL if you're moving at a constant speed, huh?

The Prius isn't optimized for highway driving. At high speeds, the transmission becomes less efficient than a conventional automatic transmission with a locking torque converter. This is because an increasing amount of power must flow through the electrical path, which, good as it may be, is not as efficient as a simple mechanical path.

 

<div class='quotetop'>QUOTE(bsoft @ Jun 9 2007, 09:21 PM) [snapback]459006[/snapback]</div>

Actually, at higher speed, LESS power flows through the electrical path. The PSD always sends 60% of the torque to the wheels, and 40% of the torque to MG1. But work is force times distance. At zero speed, just as you step on the pedal, the wheels are not moving yet, and all that torque does no work. But MG1 can spin, so its 40% of the torque does all the work, and takes all the power, converting it to electricity, sending that to MG2, which applies torque to the wheels along with the 60% of engine torque already going there. This may look inefficient, but it allows the engine to run at its design rpm, which is much more efficient.

As vehicle speed increases, the torque going to the wheels does increasingly more and more work, and thus more of the power takes that route.

The Prius is more efficient than a conventional car at highway speed as well, because the engine can be smaller than would be required for a conventional car, because MG2 and the batteries are available for those brief times when maximum power is needed.

The Prius could be made to get better mpg by reducing its overall power, but Americans won't buy a weak car. That's what you're really talking about when you compare Prius mpg to an econobox.

The OPs original point, that the Prius could have better FE if it had no emissions controls is also true, but I suspect the difference is extremely small for people who drive longer than 20 minutes or so at a time. But conventional cars are really filthy during their warm-up. The Prius is a car for the environment. In 2004 it was the very best that the technology was capable of. I think we're all expecting improvements for the 2009 model year.

If you drive such short distances that you are taking a significant hit in FE due to the emissions controls, then you should be driving an electric car!!! You'd get MUCH better FE and zero emissions.

So while the OP's original point is correct, I believe the concern is misguided.

 

<div class='quotetop'>QUOTE(bsoft @ Jun 10 2007, 01:21 PM) [snapback]459006[/snapback]</div>

I agree most of your comments, but...
I've not found a midsize vehicle yet which competes with the Prius 51 mpg highway mileage number.
Is there any? or would you please let us know why you commented Prius is "less efficient" on highway?

Ken@Japan

 

<div class='quotetop'>QUOTE(MegansPrius @ Jun 8 2007, 04:16 PM) [snapback]458285[/snapback]</div>

I just returned home from a 4800 mile trip that included driving on the plains, desert, mountains and the hill country of Texas. My overall MPG for the entire trip was 59.2
My best tank mileage was 71.4 , which was from Hereford, Texas down thru Southern N.M. and back up to Albuquerque. The worst tankful MPG was in the mountains of Southern Colorado at 49.3, and yes the Prius works great in the mountains. I only drove around 60 MPH, so I'm sure that helped, but I think you could say the Prius is optimized - at least that is good enough mileage for me

 

<div class='quotetop'>QUOTE(Per @ Jun 8 2007, 04:02 PM) [snapback]458276[/snapback]</div>

Per,
First I will agree with you that it is a valid comparison. In 1988 "a car" could get 56mpg. Why can't "a car" in 2007 get 56mpg? Second, the fuel economy of the Prius is very dependant on the driver. In yesterday's rally the range of mpg for the Prius (all hatchbacks) was at least 56.7mpg to 70.1 mpg. An Insight won at 78+ mpg. Third, diesels get better mpg than some in the Prius. I believe all (3 biodiesel & 1 stock diesel)got over 60mpg. I was stuck behind a West Philly biodiesel so I can tell you that thing put out a black cloud of smoke during acceleration. The diesels get better mpg so they pollute less than my Prius?