Featured Gen 6 Prius engine will be a “game changer,” achieve a 53% thermal efficiency

BYD had a 43% efficient engine back in 2021. The next gen being better isn't a surprise.
Development of 43% Brake Thermal Efficiency Gasoline Engine for BYD DM-i Plug-in Hybrid

The not using traditional rounding is seems to be because of one up manship with Geely. They announced a 43.32% efficient engine soon after BYD released the 43% one. There is a government org certifying these values in China. BYD has a 46.5% thermally efficient engine; the 46.06% is the production model.
Geely and BYD argue over engines, plus other fallout from PHEV tech announcement

You were the one claiming it will be 50% here.

Currently, it is in a new Seal. BYD Seal 06 - Wikipedia
I'm sure BYD will use it elsewhere.

The Metro barely beats the Prius in the combined rating. If the EPA didn't have a thing for whole numbers, the difference could be as low as 1/10 or 1/100 of a mpg.

Cd is only part of the aero equation; the other is frontal area. The Metro is two size classes smaller than the Prius; it is a half foot shorter(height) and thinner. Wind may push harder on it, put there is good amount for it to push against. Then the Metro isn't saddled with ten more years of emission regulations. Fueleconomy.gov doesn't post emission ratings for cars that old, but it probably wouldn't pass the minimum of 2004, let alone the clean rating the Prius achieved.

It also had a 0 to 60 mph time of 15 seconds. With the patience required to drive that Metro regularly, a driver in the Prius could likely reach the original mpg rating

In that light, the two being close isn't that surprising. The Metro engine is working near its thermal efficiency peak most of the time. Which leaves it with little reserve power, and low power performance. The basic hybrid concept is to use such smaller engine, and have the electric side make up for the performance limitations doing so entails.

 

Yes, yes and yes.

But that wasn't the point.

A Geo Metro has around CdA of 6.24 (the 2-door Xfi may be different) whereas the 2nd gen Prius is about 7% better at 5.83 yet the Metro Xfi also has a new highway rating of 52 mpg whereas the 2nd gen Prius is only 45 mpg, 15% lower. How does a car with 7% better total aerodynamics get 15% worse fuel mileage?

Yes, emissions regulations and such has a lot to do with it, but efficiency is efficiency. Excuses, reasons or not, one is more efficient than the other. And if we compare that efficiency with, say, a diesel freight truck, it may be even more efficient. It may be apples to oranges, but if we get a +50% efficient engine in a 3-row SUV with a CdA of 28 and that costs $98,000, that efficiency is no longer all that impressive.

 

At first glance, looks like the Prius has about a 24% larger cross section, and is about 80% heavier. And in 1994, the National 55 MPH speed had not yet been fully repealed.

 

• The overall drag on the Prius is still less, despite being bigger.
  
• Weight isn't as much of a factor as one would think, especially for highway fuel mileage ratings, but maybe you have a point here to a degree.
  
• The 52 highway MPG the the current revised fuel mileage in terms of 2024 EPA fuel mileage testing standards, which has nothing to do with 55 mph highways. The original highway fuel mileage rating in 1994 in the Geo Metro Xfi when there was a National 55 mph highway law was 58 mpg.

 

Weight and smaller tires do affect highway fuel economy, aero isn’t the only consideration.

 

I'm not sure discussing a 'Press Release" performance spec makes a lot of sense. I'll wait until we can get test articles.

Bob Wilson

 

Back during the time frame of Geo's - the EPA test was much much easier to get high ratings on. That's why the Gen 2 Prius could easily get in the 60s MPG - even though it was a much much safer car to survive an accident in as well as many more modern features as well as roominess and comfort.
Fun backstory of the old EPA rules was, it's designed to make giant land barge's poor mileage not look so egregious. Then along came the the Prius getting 60's MPG & so the big 3 insisted that it EPA get reworked to be more realistic & pull the Prius down into the 50's mpg. Cutting off their nose to despite their face.
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The EPA city test cycle is nothing like what today's drivers consider highway driving. The max speed is 60mph, but the average is 48.3mph. It dips down to as slow as 30mph. At no point is there steady speeds. Acceleration rates are slower than what the Metro can do. While it is a lot slower than what goes on a highway today, the test is just fast enough that the Prius has to spin the engine for almost the entire time.

The test was almost custom made for the Xfi. Its lighter weight will play a part in the city rating with the slow downs and speed ups. Before we get to the tests, the weight difference will affect the cars' coast down results. The Metro likely ended up with lower resistance on the dynamometer. The Civic VX was available with the Metro. The Xfi could have been trading pollution for efficiency too.

For the Prius aero advantage to be seen, we would need to see the cars' fuel consumption at steady state speeds at 60mph and above. The Prius does beat the Geo in the city ratings. Enough that their original combined ratings were the same.

Slow acceleration, manual only, possible lack of A/C lead to low sales for the Xfi, and GM canceling it before the rest of the line up. The gen2 Prius had waiting lists because it gave the efficiency without the compromises.

 

Looks our posts were mere seconds apart. Great minds rebut alike

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