Do higher NO_x numbers explain Eco's much superior fuel efficiency?

We don't even know the Eco has a lean burn engine.

 

First Kudos to Consumer Reports who at least honored the Nov 8, press embargo by publishing later, November 18th. But everyone has had to deal with the slow release of information. It wasn't until January that we got access to the EPA "Test Car Database" that gave us the emissions data. Then in February the New Car Features that told us about the fuel mixture sensor.

It is impossible to identify a single change that gave a specific MPG increase. Rather the sum of the parts, the incremental changes, gives the performance improvement. But understand I am not a Consumer Reports fan as other publications and reporters have done much more with less.

Bob Wilson

 

Do we know what the difference in EPA fuel consumption between the Eco and the other models actually is?

With rounded numbers of 52 and 56 mpg, the actual difference could be anywhere between 3 and 5 mpg.

 

..this thread has more info
Prius FE Answers buried in the EPA Test Car Database | Page 2 | PriusChat

 

The data source used for that thread, was posted here with nothing stripped. Which makes is tougher read, but shows the Eco model emitting more NOx. But we are talking miniscule amounts to begin with, and the Eco has the same smog rating as the others.

So the Eco numbers could be the result of trading off the emissions a little bit, for a little bit improvement of fuel economy, or the results are within range of each other to be considered statistically the same.

But there is no actual lean burn mode proposed in the OP of the thread. It would require a different emission control system to clean up that much NOx, and frankly, the Eco MPG rating would be disappointing if lean burn was being used.

The gen4 is up on Fueleconomy.gov now, so we can check engine codes under the environment section.
The Eco is GTYXV01.8PC4.
The others are GTYX01.8PC3 and GTYX01.8PC4.
The hybrid battery is counted as part of the emission of the emission system. So the two different codes for the others is for the NiMH and Li-ion batteries. The Eco shares the code with the other Li-ion. So it has the same emission system as the others. Without extra equipment to clean up the NOx actual lean burn would produce, it couldn't make use of it and retain the same smog score.

So the Eco does not have a lean burn mode.

 

Thankfully, we are not reduced to intuition, we have the facts. Aerodynamics and weight reduction are Toyota's explanation, and the EPA's explanation. Feel free to try to show that 35 PSI is 'over inflated' in any sense, we will wait.

 

If Toyota had a secret way to get better gas mileage on every Prius, it would use it on every Prius, they could sell more.

Instead, Toyota carefully 'rations' weighty options, you can't get 17 inch wheels and the moon roof on the same Prius, so that they do not have to lower MPG estimates. By aggressively rationing options, the Two Eco manages to slip into a higher Estimate, no magic, no secret sauce, just careful choices. (sadly owners who, like you, think there is a 'secret', buy an Eco with the plan to put the spare tire back in, negating most of the advantage of an Eco)

You could test this yourself in your current car, by having a loved one take out the spare tire and jack randomly while they document the odometer reading and let you do 'blind' MPG recording, never knowing when the car was lighter. (Taking out the rear windshield wiper motor and washer pump motor or changing wheel size will leave a mark, making it harder to do 'blind' recording)

Car Bibles: Get better gas mileage - improve your mpg

 

I have installed full size spare tire with my Two Eco and nothing has change in regards with Mpg and I'm also inflating all tires around 35psi for better ride.

 

If it is legal for one model, it would be legal for all models.
Now would be an insanely bad time to introduce a a foreign car that did not pass EPA standards.
VW Faces $17B Fine for Emissions Scam | PriusChat

Merged

So, $500 decals?

 

Its gotta be something else more besides the weight, I bought ECo model for lithium ion battery and 3 doors smart key worth $500 imho.

 

Whew, I was worried you bought it for the gas mileage you negated.

Toyota does mention other gains besides weight loss: energy conserving glass, and aerodynamic improvements, they are considered minor, but Toyota thought them worthwhile.

Of all the features I lost moving to a v Three, 3 door SKS is the one I miss most.

 

The EPA data base confused me because eco is in different weight class, which apparently impacts test conditions, so for me personally, I am still unclear on it.

 

How do you know? Have you tried increasing the tire pressure and testing the difference. I see one on my car, and the higher the base MPG rating, the higher the whole number increase will be from it.

What would be so dirty? The cars have the same smog score, and that is what most people would see, if they even cared enough to look into it.

The only people that would care, are those that want to brag about the Prius being cleaner than other models that happen to be in the strictest emissions bin that an ICE car can achieve

You started the thread. The burden is on you to prove your hypothesis. With the Eco and the other Li-ion models having the same engine code, they have the same equipment. If you think that is in error, then you have to find the evidence to disprove it.

Weight class doesn't effect EPA test conditions. The car's actual weight does when determining those. Weight class has more to do with determining which models have to be tested.

Toyota limits options on the Touring models in order to keep them in the same weight class as the 'regular' trims. This way they can use the regular MPG numbers on the Touring window stickers. Yep, this is what Ford did with the Fusion hybrid and C-max numbers. The Eco falls into a different weight class. So even if there was no difference in fuel economy, it would still need a separate EPA entry. I suspect this was the case with the Camry hybrids. The weight difference was enough between the LE and the others that Toyota had to do a separate listing, not because they chose too.

 

It could be psychological. People who buy the eco naturally drive more efficient therefore the eco gets better milage.

 

it has to be epa testing, or another agency. peeps buying the eco have no way of knowing if it gets better mileage than non eco.

 

I never thought the Prius Eco would have higher NOx emissions than the normal Prius, because no lean burn is involved. Lean burn is why the 5-speed Honda Insight was rated ULEV instead of SULEV, like it's CVT version. Lean burn can have an air/gas mix up to 25.8 to 1 instead of the usual 14.7 to 1.